bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional diversity of benthic assemblages
Authors: Gray John S. , Elliott Michael
Published: November 2020

Now that we have discussed how assemblages of marine soft sediments are structured, we need to consider functional aspects. There are a few main interrelationships that need to be discussed here— inter- and intraspecific competition, feeding and predator–prey interactions, the production of biomass, and the production and delivery of recruiting stages. Other functional aspects, such as the effects of pathogens and parasites and the benefits of association (mutualism, parasitism, symbiosis, etc.) are of less importance in the present discussion. By function we mean the rate processes (i.e. those involving time) that either affect (extrinsic processes) or are inside (intrinsic processes and responses) the organisms that live in sediments. Hence these include primary and secondary production and processes that are mitigated by the organisms that live in sediments, such as nutrient and contaminant fluxes into and out of the sediment. We begin with the historical development of the field since such aspects are often overlooked in these days of electronic searches for references. Functional studies of ecosystems really began with Lindeman´s classic paper (1942) on trophic dynamics. Rather than regarding food merely as particulate matter, Lindeman expressed it in terms of the energy it contained, thereby enabling comparisons to be made between different systems. For example, 1 g of the bivalve Ensis is not equivalent in food value to 1 g of the planktonic copepod Calanus, so the two animals cannot be compared in terms of weight, but they can be compared in terms of the energy units that each gram dry weight contains. The energy unit originally used was the calorie, but this has now been superseded by the joule (J), 1 calorie being equivalent to 4.2 joules. Ensis contains 14 654 J g-1 dry wt and Calanus 30 982 J g-1 dry wt. The basic trophic system is well understood and can be summarized as we showed earlier in Fig. I.8 which gives the links between various trophic levels and the role of competition, organic matter transport, and resource partitioning. In systems fuelled by photosynthesis (so excluding the chemosynthetic deep-sea vent systems), the primary source of energy for any community is sunlight, which is fixed and stored in plant material, which thus constitutes the first trophic level in the ecosystem.
Human impacts on soft-sediment systems—pollution
Authors: Gray John S. , Elliott Michael
Published: November 2020

A widely accepted definition of marine pollution is “the introduction by man, directly or indirectly, of substances or energy into the marine environment (including estuaries) resulting in such deleterious effects as harm to living resources, hazards to human health, hindrance to marine activities including fishing, impairment of the quality for use of seawater, and reduction of amenities”. (Wells et al. 2002). This differs from contamination since it results in biological damage, whether to the natural or human system, whereas contamination can be regarded merely as the introduction of substances by human activities (McLusky and Elliott 2004). Furthermore, pollution and pollutants can refer to biological and physical materials as well as chemicals (Gray 1992, Elliott 2003). In the case of the benthos, there is an extensive literature indicating that every type of pollutant has an effect on the benthos and so it is not surprising that the benthos is the mainstay of any monitoring and investigative programme. Pollution can affect organisms living in sediments by physical variables associated with the pollution source, such as increased sedimentation of particles, which leads to smothering of the fauna. In such cases the effect can in fact be regarded as a disturbing factor if the effects lead to mortality of individuals (Gray 1992). Alternatively, pollution can affect the fauna by toxicity where increased concentrations of contaminants lead to biochemical and physiological effects and ensuing mortality if certain thresholds for adaptation are exceeded. Here, however, we first treat the effects of the most widespread form of pollution affecting the marine environment— increased organic matter in sediments. Excess organic matter enters the marine environment principally as sewage, although it can also include waste from paper pulp mills or changed river run-off, for example. Excess organic matter causes physical effects such as smothering and also leads to reduced oxygen concentrations in the water column or pore-water in sediments. Sewage discharged into confined bodies of water frequently leads to the well-known symptoms termed eutrophication, resulting, in the most extreme cases, in a total lack of oxygen and the presence of hydrogen sulfide in the sediment, with a corresponding absence of fauna (e.g. de Jonge and Elliott 2001).
The benthos in the management of marine sediments
Authors: Gray John S. , Elliott Michael
Published: November 2020

Throughout the previous chapters, we have focused on our understanding of the benthic system, its processes, structure, and functioning but, hopefully, we have also shown some of the changes to the system as the result of human activities. It is now relevant to look at the way in which management relies on and uses benthic data and information, the way in which benthic information and data are put into a wider context, and the way we manage marine sediments. Although examples in this chapter are mainly taken from European initiatives, the same examples exist in other regions. In all countries, there are many agencies and bodies involved directly or directly in the science and management of marine sediments—some carry out marine benthic studies and/or the monitoring, some require others to carry out the monitoring, and others use the benthic research and monitoring information. Throughout this book we have indicated many of the numerical techniques at our disposal for analysing benthic data, for linking them to the environmental variables, and for using them in understanding the functioning of the marine system, not least in relation to human activities. Indeed, Elliott (1996) suggested that there were approximately 26 groups of techniques for analysing the benthos and Gray (2000) describes recent methods and the progress made recently in analysing benthic data—by now we have added even more techniques. We have indicated here how some of the techniques have been adapted from other fields of ecology, such as terrestrial systems and even, in some cases, from other fields altogether; for example the main diversity index used, Shannon–Wiener H',was obtained from information and systems analysis. Figure 11.1 indicates how many of those methods link together in order to obtain a large amount of information from the benthos—it is axiomatic that no single technique gives a large amount of information and many of them rely on several techniques being used together. Figure 11.1 indicates how we start with community structural and primary variables (abundance, biomass, etc.) and move on from these into univariate and derived community variables as well as graphical techniques for community structure.
Introduction and Background
Authors: Kaye Phillip , Laflamme Raymond , Mosca Michele
Published: November 2020

A computer is a physical device that helps us process information by executing algorithms. An algorithm is a well-defined procedure, with finite description, for realizing an information-processing task. An information-processing task can always be translated into a physical task. When designing complex algorithms and protocols for various information-processing tasks, it is very helpful, perhaps essential, to work with some idealized computing model. However, when studying the true limitations of a computing device, especially for some practical reason, it is important not to forget the relationship between computing and physics. Real computing devices are embodied in a larger and often richer physical reality than is represented by the idealized computing model. Quantum information processing is the result of using the physical reality that quantum theory tells us about for the purposes of performing tasks that were previously thought impossible or infeasible. Devices that perform quantum information processing are known as quantum computers. In this book we examine how quantum computers can be used to solve certain problems more efficiently than can be done with classical computers, and also how this can be done reliably even when there is a possibility for errors to occur. In this first chapter we present some fundamental notions of computation theory and quantum physics that will form the basis for much of what follows. After this brief introduction, we will review the necessary tools from linear algebra in Chapter 2, and detail the framework of quantum mechanics, as relevant to our model of quantum computation, in Chapter 3. In the remainder of the book we examine quantum teleportation, quantum algorithms and quantum error correction in detail. We are often interested in the amount of resources used by a computer to solve a problem, and we refer to this as the complexity of the computation. An important resource for a computer is time. Another resource is space, which refers to the amount of memory used by the computer in performing the computation. We measure the amount of a resource used in a computation for solving a given problem as a function of the length of the input of an instance of that problem.
Introductory Quantum Algorithms
Authors: Kaye Phillip , Laflamme Raymond , Mosca Michele
Published: November 2020

In this chapter we will describe some of the early quantum algorithms. These algorithms are simple and illustrate the main ingredients behind the more useful and powerful quantum algorithms we describe in the subsequent chapters. Since quantum algorithms share some features with classical probabilistic algorithms, we will start with a comparison of the two algorithmic paradigms. Classical probabilistic algorithms were introduced in Chapter 1. In this section we will see how quantum computation can be viewed as a generalization of probabilistic computation. We begin by considering a simple probabilistic computation. Figure 6.1 illustrates the first two steps of such a computation on a register that can be in one of the four states, labelled by the integers 0, 1, 2, and 3. Initially the register is in the state 0. After the first step of the computation, the register is in the state j with probability p0,j . For example, the probability that the computation is in state 2 after the first step is p0,2. In the second step of the computation, the register goes from state j to state k with probability qj,k. For example, in the second step the computation proceeds from state 2 to state 3 with probability q2,3. Suppose we want to find the total probability that the computation ends up in state 3 after the second step. This is calculated by first determining the probability associated with each computation ‘path’ that could end up at the state 3, and then by adding the probabilities for all such paths. There are four computation paths that can leave the computation in state 3 after the first step. The computation can proceed from state 0 to state j and then from state j to state 3, for any of the four j ∊ {0, 1, 2, 3}. The probability associated with any one of these paths is obtained by multiplying the probability p0,j of the transition from state 0 to state j, with the probability qj,3 of the transition from state j to state 3.
Algorithms Based on Amplitude Amplification
Authors: Kaye Phillip , Laflamme Raymond , Mosca Michele
Published: November 2020

In this section, we discuss a broadly applicable quantum algorithm that provides a polynomial speed-up over the best-known classical algorithms for a wide class of important problems. The quantum search algorithm performs a generic search for a solution to a very wide range of problems. Consider any problem where one can efficiently recognize a good solution and wishes to search through a list of potential solutions in order to find a good one. For example, given a large integer N, one can efficiently recognize whether an integer p is a non-trivial factor of N, and thus one naive strategy for finding non-trivial factors of N is to simply search through the set {2, 3, 4, . . . , ⌊√N⌋} until a factor is found. The factoring algorithm we described in Chapter 7 is not such a naive algorithm, as it makes profound use of the structure of the problem. However, for many interesting problems, there are no known techniques that make much use of the structure of the problem, and the best-known algorithm for solving these problems is to naively search through the potential solutions until one is found. Typically the number of potential solutions is exponential in the size of the problem instance, and so the naive algorithm is not efficient. Often the best-known classical search makes some very limited use of the structure of the problem, perhaps to rule out some obviously impossible candidates, or to prioritize some more likely candidates, but the overall complexity of the search is still exponential. Quantum searching is a tool for speeding up these sorts of generic searches through a space of potential solutions. It is worth noting that having a means of recognizing a solution to a problem, and knowing the set of possible solutions, means that in some sense one ‘knows’ the solution. However, one cannot necessarily efficiently produce the solution. For example, it is easy to recognize the factors of a number, but finding those factors can take a long time. We give this problem a more general mathematical structure as follows.
Animal–plant interactions
Authors: Maun M. Anwar
Published: November 2020

Population dynamics of plant species of coastal sand dunes is influenced directly, both above and below the soil surface, by a wide variety of organisms. Plants serve as sources of carbon and pathogens including viruses, insects, bacteria, fungi, birds, and mammals of various kinds. Some enhance plant performance while others have deleterious effects. Positive interactions include pollination of flowers by useful insects in return for nectar and pollen, nutrient acquisition from soil by mycorrhizal fungi in exchange for carbon and acquiring nitrogen (N) from N-fixing bacteria. In the history of co-evolution between plants and organisms over one hundred million years plants have developed many mechanisms to defend themselves from pathogens. Morphology may be altered by producing epicuticular waxes, developing trichomes over leaves, producing tough leaves with deposition of celluloses, lignin, suberin and callose, developing thorns on stems and branches or producing secondary plant metabolites that retard development, intoxicate or kill herbivorous insects. Herbivory may induce a plant to produce chemicals that signal to advertise the presence of insects feeding on them and attract parasites to reduce their numbers. Phenological escape is also employed, such as delay of leaf expansion during periods of insect abundance. Some indirect mechanisms of plant defence involve the use of insects such as ants for protection from other phytophagous insects. However, the predators have also evolved the ability to break down the defence mechanisms of the plant. For example, they may use phytochemicals for their own defence or as olfactory clues for feeding. In this chapter a brief account of organisms of the coastal dune communities, including species of the intertidal zone, scavengers of the sea coast, reptiles, birds, insects, mammals and their possible interactions with terrestrial vegetation is presented. For biological organisms of the seashore the intertidal zone is the most important for food and shelter. The sand-dwelling species of the seashore must be able to contend with four limiting factors: (i) rush of water from the approaching or receding high tide and pounding breakers, (ii) low salinity of the top surface of sand (iii) desiccation of surface by high winds and sunshine and (iv) extreme changes in temperature of topsoil.
Dune systems in relation to rising seas
Authors: Maun Anwar , Fahselt Dianne
Published: November 2020

Beaches and associated dunes are constituted of unconsolidated materials, such as sand, and thus are low-strength land forms less robust than rocky cliffs (van der Meulen et al. 1991). It is estimated that 70% of sand-based coastlines in the world are presently subject to erosion (Bird 1985; Wind and Peerbolte 1993). However, natural dune systems are inclined to adjust after stress without permanent damage (Brown and McLachlin 2002), and when stabilized by plant cover they offer a first line of coastal defence against assault from wave action (Wind and Peerbolte 1993; Broadus 1993; De Ronde 1993). Natural self-sustaining dune systems interact with the sea and closely reflect changes in sea levels. At any given time no single sea level characterizes all oceans, that is, the resting position of the ocean surface, or geoid, is not uniformly elevated over the earth. Eustatic sea levels, free of influence from tides, waves and storms, thus vary from place to place as well as over time. Satellite altimetry, which permits more accurate as well as more numerous observations than older tide-gage methods of measuring sea levels, shows that the ocean is actually a spheroid modified by depressions and elevations. For example, in parts of the Indian Ocean sea levels are as much as 70 m lower than the global mean and in the North Atlantic 80 m higher (Carter 1988). Climate is governed by long-term periodic variations in the earth’s orbit that effect changes in solar radiation and, consequently, also in sea levels (Bartlein and Prentice 1989; Woodroffe 2002). As a result, ice ages repeatedly alternate with periods of interglacial warming in which ice masses contract and sea levels increase. Most of the time that has passed since the Cambrian period—approximately 500 million years—sea levels, although fluctuating on several timescales, have been higher than they are today. Because of the difficulties in documenting conditions so far in the distant past estimates of these sea levels vary considerably, but those shown in Fig. 13.1, based on different kinds of evidence, are representative of attempts at reconstruction (personal communication RA Rohde 2008).
Observation selection effects and global catastrophic risks
Authors: ćirković Milan M.
Published: November 2020

Different types of global catastrophic risks (GCRs) are studied in various chapters of this book by direct analysis. In doing so, researchers benefit from a detailed understanding of the interplay of the underlying causal factors. However, the causal network is often excessively complex and difficult or impossible to disentangle. Here, we would like to consider limitations and theoretical constraints on the risk assessments which are provided by the general properties of the world in which we live, as well as its contingent history. There are only a few of these constraints, but they are important because they do not rely on making a lot of guesses about the details of future technological and social developments. The most important of these are observation selection effects. Physicists, astronomers, and biologists have been familiar with the observational selection effect for a long time, some aspects of them (e.g., Malmquist bias in astronomy or Signor-Lipps effect in paleontology) being the subject of detailed mathematical modelling. In particular, cosmology is fundamentally incomplete without taking into account the necessary ‘anthropic bias’: the conditions we observe in fundamental physics, as well as in the universe at large, seem atypical when judged against what one would expect as ‘natural’ according to our best theories, and require an explanation compatible with our existence as intelligent observers at this particular epoch in the history of the universe. In contrast, the observation selection effects are still often overlooked in philosophy and epistemology, and practically completely ignored in risk analysis, since they usually do not apply to conventional categories of risk (such as those used in insurance modelling). Recently, Bostrom (2002a) laid foundations for a detailed theory of observation selection effects, which has applications for both philosophy and several scientific areas including cosmology, evolution theory, thermodynamics, traffic analysis, game theory problems involving imperfect recall, astrobiology, and quantum physics. The theory of observation selection effects can tell us what we should expect to observe, given some hypothesis about the distribution of observers in the world. By comparing such predictions to our actual observations, we get probabilistic evidence for or against various hypotheses.
The continuing threat of nuclear war
Authors: Cirincione Joseph
Published: November 2020

The American poet Robert Frost famously mused on whether the world will end in fire or in ice. Nuclear weapons can deliver both. The fire is obvious: modern hydrogen bombs duplicate on the surface of the earth the enormous thermonuclear energies of the Sun, with catastrophic consequences. But it might be a nuclear cold that kills the planet. A nuclear war with as few as 100 hundred weapons exploded in urban cores could blanket the Earth in smoke, ushering in a years-long nuclear winter, with global droughts and massive crop failures. The nuclear age is now entering its seventh decade. For most of these years, citizens and officials lived with the constant fear that long-range bombers and ballistic missiles would bring instant, total destruction to the United States, the Soviet Union, many other nations, and, perhaps, the entire planet. Fifty years ago, Nevil Shute’s best-selling novel, On the Beach, portrayed the terror of survivors as they awaited the radioactive clouds drifting to Australia from a northern hemisphere nuclear war. There were then some 7000 nuclear weapons in the world, with the United States outnumbering the Soviet Union 10 to 1. By the 1980s, the nuclear danger had grown to grotesque proportions. When Jonathan Schell’s chilling book, The Fate of the Earth, was published in 1982, there were then almost 60,000 nuclear weapons stockpiled with a destructive force equal to roughly 20,000 megatons (20 billion tons) of TNT, or over 1 million times the power of the Hiroshima bomb. President Ronald Reagan’s ‘Star Wars’ anti-missile system was supposed to defeat a first-wave attack of some 5000 Soviet SS-18 and SS-19 missile warheads streaking over the North Pole. ‘These bombs’, Schell wrote, ‘were built as “weapons” for “war”, but their significance greatly transcends war and all its causes and outcomes. They grew out of history, yet they threaten to end history. They were made by men, yet they threaten to annihilate man’.
A Darwinian Prediction
Authors: Weiner J. S. , Stringer Chris
Published: November 2020

On 18 December 1912 Arthur Smith Woodward and Charles Dawson announced to a great and expectant scientific audience the epoch-making discovery of a remote ancestral form of man—The Dawn Man of Piltdown. The news had been made public by the Manchester Guardian about three weeks before, and the lecture room of the Geological Society at Burlington House was crowded as it has never been before or since. There was great excitement and enthusiasm which is still remembered by those who were there; for, in Piltdown man, here in England, was at last tangible, well-nigh incontrovertible proof of Man’s ape-like ancestry; here was evidence, in a form long predicted, of a creature which could be regarded as a veritable confirmation of evolutionary theory. Twenty years had elapsed since Dubois had found the fragmentary remains of the Java ape-man, but by now in 1912 its exact evolutionary significance had come to be invested with some uncertainty and the recent attempt to find more material by the expensive and elaborate expedition under Mme. Selenka had proved entirely unsuccessful. Piltdown man provided a far more complete and certain story. The man from Java, whose geological age was unclear, was represented by a skull cap, two teeth, and a disputed femur. Anatomically there was a good deal of the Piltdown skull and, though the face was missing, there was most of one side of the lower jaw. The stratigraphical evidence was quite sufficient to attest the antiquity of the remains; and to support this antiquity there were the animals which had lived in the remote time of Piltdown man; there was even evidence of the tool-making abilities of Piltdown man. In every way Piltdown man provided a fuller picture of the stage of ancestry which man had reached perhaps some 500,000 years ago. Dawson began by explaining how it came about that he had lighted on the existence of the extremely ancient gravels of the Sussex Ouse: . . . ‘I was walking along a farm-road close to Piltdown Common, Fletching (Sussex), when I noticed that the road had been mended with some peculiar brown flints not usual in the district. . . .
Diagnosis, prognosis, and care planning: ‘information processing’
Authors: Banerjee Avijit , Watson Timothy F.
Published: November 2020

Once a general and targeted history, examination, and investigations have been carried out (‘information gathering’), it is time for the dentist and their oral healthcare team to assimilate all of the relevant information in order to formulate a diagnosis, prognosis, and care plan for the individual patient (‘information processing’). Although the detection and diagnostic phases are each discussed separately in this book, an experienced clinician will often accomplish both phases simultaneously. It is vital to remember that diagnosis precedes treatment in all cases. Diagnosis is the art or act of inferring, from its signs and symptoms or manifestations, the nature or cause of an illness or condition. This stage is critical in order to allow the dental team and the patient to appreciate the nature, cause, and severity of the illness or condition. The prognosis is the forecast of the course of a disease or the patient’s response to treatment of the disease. This stage helps the dentist and the patient to understand how easy or difficult the treatment will be to carry out, and it allows assessment of the patient’s motivation to cure the problem. In dentistry, the oral healthcare team can only start the patient off on the road to recovery by restoring form and function to their dentition as well as helping the patient to prevent or control the disease process, so preventing its return. It is then up to the patient whether they follow this advice and maintain their oral health in the future. This plan is the formal itemized management strategy, developed by the dentist and their oral healthcare team, for the individual patient to treat the manifestations of a disease and to control it or prevent it from recurring. It can be divided into phases of therapy (e.g. prevention or control, stabilization or definitive treatment, and review, reassessment, or recall), and it should be adapted and modified during its execution for maximum benefit to the patient. It should take into account unforeseen developments in the course of the disease or the patient’s response to care. It should be written down and made clear to all parties for discussion, so that informed consent can be gained prior to implementation.
Essentials of minimally invasive operative dentistry
Authors: Banerjee Avijit , Watson Timothy F.
Published: November 2020

All members of the oral healthcare team have a part to play in patient management, and the team is comprised of the lead dentist (plus other colleagues in the dental practice), the dental nurse, hygienist, receptionist, laboratory technician, and possibly a dental therapist. In the UK, registered dental nurses can take further qualifications in teaching, oral health education, and radiography, and can specialize in other aspects of dentistry, including orthodontics, oral surgery, sedation, and special care. If the dentist wishes to have a second specialist opinion regarding a difficult diagnosis, formulating a care plan or even executing it, they may refer the patient to a specialist dentist working in another practice, or to a hospital-based consultant specialist in restorative dentistry. These specialists have undergone further postgraduate clinical and academic training and gained qualifications enabling them to be registered as specialists with the General Dental Council (GDC) in the UK in their specific trained fields (e.g. endodontics, periodontics, prosthodontics), or have further specialist training in restorative dentistry. The lead dentist will act as a central hub in the coordinating wheel of patient management, possibly outsourcing different aspects of work to relevant specialist colleagues, as spokes of that wheel. This is the clinical environment in which patients are diagnosed and treated. This room has traditionally been known as the ‘dental surgery’, but a more appropriate modern description might be the ‘dental clinic’, as much of the more holistic care offered to patients within its four walls will be non-surgical in the first instance. The operator and nurse must work closely together. To be successful, each must build up an understanding of how the other works. The clinic consists of a dental operating chair with an attached or mobile bracket table carrying the rotary instruments and 3-1 air/water syringe (and possibly the light-cure unit and ultrasonic scaler), work surfaces (which should be as clutter-free as possible for good-quality infection control; see later), cupboards for storage, and two sinks, one for normal hand washing and another for decontaminating soiled instruments prior to sterilization. Often the surgery will also house an X-ray unit for taking intra-oral radiographs. Most clinics are designed to accommodate right-handed practitioners, in terms of the location of many of the instruments and controls.
Restorative materials and their relationship to tooth structure
Authors: Banerjee Avijit , Watson Timothy F.
Published: November 2020

Modern restorative materials can be classified in several ways, in terms of their retention (chemically adhesive, macro-, micro- or even nanomechanical), their chemistry (e.g. resin-based vs. acid–base reaction, filler particles), or their clinical properties (e.g. aesthetics, strength, handling). It is essential that these materials are considered closely with the histological substrate to which they will adhere or with which they will interact, in order to understand the complexities of each system and their potential clinical uses. This chapter will outline and discuss aspects of dental materials science to enable the reader to understand and appreciate the links with relevant histology and relate this to the clinical aspects of minimally invasive operative dentistry. Also discussed is dental amalgam, still a popular restorative material among many dentists worldwide, although clinical indications for its use are becoming more limited as treatment rationales change and adhesive materials improve. This text will require supplementation from suitable dental histology and detailed dental material science texts. Dental resin composites are aesthetic, plastic adhesive restorative materials that consist of co-polymerized methacrylate-based resin chains embedding inert filler particles (conferring strength and wear resistance) and requiring a separate adhesive (bonding agent) to micro-/ nano-mechanically bond them to either enamel or dentine, respectively. However, not all modern dental composites are based purely on this methacrylate resin chemistry (see Section 7.2.6). Therefore the term ‘composite resin’ is inappropriate and should not be used. Resin composites have developed over the past 50 years, after the introduction of the acid-etch technique (Buonocore, 1955) and methacrylate monomers (Bowen’s resin—Bis-GMA (1971); see Section 7.2.2). The unset (or uncured) material consists of a mixture of several different types of resin methacrylate monomers, most of which are hydrophobic (water-hating) in nature (see Figure 7.1). The monomer chain length affects certain properties of the resin composite:… • Viscosity (or flowability) of the material. This is important in order to minimize voids trapped within the uncured composite during placement and packing within the depths of a cavity (the stiffer the consistency, the greater the risk of trapping air voids). The shorter the uncured monomer length (and therefore the lower the molecular weight), the lower is its viscosity. Often shorter-length, lower-molecular- weight methacrylate monomers form the basis of the resin chemistry of flowable resin composites, and other diluent molecules may be added.
Blackout
Authors: Farne Hugo , Norris-Cervetto Edward , Warbrick-Smith James
Published: November 2020

Note that the terms ‘syncope’ and ‘loss of consciousness’ are not interchangeable as loss of consciousness can be due to either syncopal or non-syncopal causes. Syncope is a form of loss of consciousness in which hypoperfusion of the brain is the cause (from the Greek syn (together) and kopein (to cut), referring to the fact that the blood flow that joins the brain together with the rest of the body has been cut). Syncopal causes can be subdivided by mechanism as follows: • ‘Reflex’: this is believed to involve activation of a primitive reflex that leads mammals to ‘play dead’ when faced with danger. Their heart rate slows and their blood pressure drops temporarily, reducing cerebral perfusion and leading to syncope. Some people appear to have a low threshold for activating this reflex in specific situations—for example after standing still for a long time, after seeing something frightening (e.g. blood, needles), or when straining (micturition, defecation). • ‘Cardiac’: pathologies causing a reduction in cardiac output (such as arrhythmias or outlet obstruction) can also lead to syncope. • ‘Orthostatic’: orthostatic hypotension basically means low blood pressure on sitting or standing (as opposed to lying flat). When we stand up there is a sudden drop in blood pressure that we compensate for by vasoconstriction, particularly of the ‘capacitance’ veins in the legs. This reduces the intravascular space, enabling us to maintain the pressure. However, this vasoconstriction takes a few seconds, so to prevent a transient fall in blood pressure every time we stand, there is a temporary increase in heart rate. Patients with reduced intravascular volume (e.g. from dehydration) and/or in whom the normal autonomic response (transient tachycardia and peripheral vasoconstriction) to standing is blunted (e.g. due to drugs or autonomic neuropathy) are vulnerable to blackouts. • ‘Cerebrovascular’: these are non-cardiac structural causes of reduced cerebral perfusion, i.e. obstructions to the blood flow between the heart and the brain. They are relatively uncommon. The main causes of a transient loss of consciousness are summarized in Figure 3.1, with the most common in large font. You should also remember that patients may believe they have lost consciousness when in fact they haven’t.
Wrestling with the Author
Authors: Rose Jonathan
Published: November 2020

Even if the Old Testament is the word of God, many of the characters in that story had an exasperating fondness for arguing with the author—and winning. Abraham sharply questions His plan to destroy Sodom, and makes Him promise to spare the city if fifty righteous men can be found, eventually bargaining Him down to ten. When God instructs Moses to liberate His people, Moses at first pleads a lack of eloquence, but evidently he’s a good enough talker to persuade the Boss to assign him Aaron as an assistant. And Job quite rightly questions why he should be the innocent victim of what seems an incredibly cruel wager. Jacob wrestles with an angel, who turns out to be the Deity undercover. In spite of a dislocated hip, Jacob wins both the match and a new title: God renames him Israel, which literally means “He who struggles with God.” (That explains a lot about Israel today.) This orneriness carried over to the Talmud, which carries on interminable and detailed debates over the interpretation of reading matter. The Bar Mitzvah likewise requires offering a new and original take on a classic text, an excellent preparation for careers in academia, the law, or revolutionary movements. You can trace this kind of damnably independent reading at least as far back as the destruction of the Second Temple in Jerusalem. Rabbi Yochanan ben Zakkai, a key figure in the transition to rabbinic Judaism, was celebrated in the Babylonian Talmud for his omnivorous reading, which was by no means limited to theology: “Scripture, Mishna, Talmud, Halacha, Aggadah, Biblical grammar, scribal traditions, deductive logic, linguistic connections, astronomical calculations, gematriot [numerology], incantations for angels, incantations for demons, incantations to palm trees, proverbs of washerwomen, proverbs of foxes,” not to mention legal treatises and chariot-repair manuals. The premise behind his reading—polymathic, multidisciplinary, ranging freely across high to low culture—is that all of it had educational value that could be shared with other readers: “That I may cause those that love me to inherit substance, and that I may fill their treasuries.”
Dreamers of the Ghetto
Authors: Rose Jonathan
Published: November 2020

This chapter does not pretend to offer a complete history of the African-American common reader. It only sketches in a few outlines of a much bigger story. But when that history is written, it will inevitably have to confront this painful contradiction. The woman who did more than any contemporary American to promote reading was raised by a mother who hated books. For an explanation, we might begin by looking to Frederick Douglass’s classic autobiography. Once he realized that most slave-owners feared black literacy, “I understood the pathway from slavery to freedom,” and determined, “at whatever cost of trouble, to learn how to read.” He developed strategies to acquire literacy surreptitiously, offering bread to poor white boys in return for reading lessons. And in The Columbian Orator, an anthology of great speeches, he found inspirational literature that spoke directly to his condition, in particular Sheridan’s philippics for Catholic emancipation. However, later he fell into the hands of a more brutal master, who completely (but temporarily) broke his desire to read: “My natural elasticity was crushed, my intellect languished, the disposition to read departed, the cheerful spark that lingered about my eye died; the dark night of slavery closed in upon me; and behold a man transformed into a brute!” In another slave narrative, Leonard Black testified that when he bought something to read, his master “made me sick of books by beating me like a dog . . . He whipped me so very severely that he overcame my thirst for knowledge, and I relinquished its pursuit,” at least until he escaped from bondage. So there were two possible and polar opposite responses to the terror campaign against black readers. One was to acquire literacy at all costs and by any means necessary. “I do begrudge your education,” admitted a black steamboat steward as he served lunch to a white college student. “I would steal your learning if I could.”4 But others internalized the whippings and developed a fear of and aversion to books. These are both legacies of slavery, and they both survived far beyond the slave era.
Fire and the Coming of the Modern World
Authors: Scott Andrew C.
Published: November 2020

What kind of world dawned after the K/P boundary? We know from studies across localities in the USA that there is evidence of frequent wildfires continuing into the earliest Paleogene. But what happened to the atmospheric oxygen level after recovery from the K/P mass extinction—did it remain above modern levels? Were we still in a high-fire world? If there were fires, what is the evidence in the charcoal record, and do we know anything about the vegetation that was burning? When the charcoal in the coal database was originally compiled, one of the important issues was how we recorded and represented our data. Early to mid-Paleocene Epoch coals (from around 65 to 55 million years ago) are often recorded as ‘earliest Tertiary’ in coal literature. (The Tertiary was the name we used to use for what we now call the Paleogene and Neogene Periods, stretching from around 65 to 1 million years ago.) However, coals that are nearer to the start of the Eocene Epoch, just older than 55 million years ago, are notoriously difficult to date. This is a problem we have with many coal sequences, as they are deposited on land, and most of the fossils used to give ages are found in marine waters. Many coals of this age are often simply recorded as coming from the late Paleocene or early Eocene. Where we have good dating information, Paleocene coals all tend to have high inertinite (charcoal) contents, well above 19 per cent. By the mid to late Eocene (50–40 million years ago), however, worldwide the charcoal contents are low, around 5 per cent or even less. There must, therefore, have been a fundamental change in the Earth system at this time. Another problem is the way in which we chose to represent our data and show the calculated oxygen curve. In order to get sufficient data to plot the curves we decided to use 10-millionyear bins. This was not a problem for the Paleozoic–Mesozoic transition, covering the great Permian mass extinction, which took place 250 million years ago.
Welcome to the Croft!
Authors: Kiddey Rachael
Published: November 2020

It was one of those days, typical of England, when you have to work very hard to remember that above the thick, white cloud the sky is always blue. I was cycling up Cheltenham Road, feeling increasingly angry, when I saw a giant advertising hoarding had been erected around a disused car showroom that had, until recently, been a residential squat. It read: ‘New Development, a mix of 1, 2 and 3 bedroom flats. Prices start at just £199,000’. The advert included pictures of smart-looking kitchens, shiny surfaces, and anonymous faces grinning inanely at their fictional bathtubs. I started to cycle harder with each raging thought. I had woken up feeling dismal and my mood had become progressively worse as the day went on. At that time, I worked as a junior programme maker at BBC Radio 4. I had been told in a meeting that I needed to establish a ‘celebrity angle’ on a story that I was working on. It maddened me. What relevance do celebrities have to ordinary people’s lives? This was 2007. The Global Financial Crash was just months away. Back then I resembled a slightly scruffy, more politically engaged Bridget Jones. Single and painfully middle class, I smoked roll-up cigarettes and spent most of my time feeling frustrated that both national and international politics appeared to be moving to the Right while I, and millions of others, protested but got nowhere. Massive peaceful anti-war protests had been ignored by Britain’s ruling elite, and direct action carried increased risk of criminalization. Some saw violence as a resort—albeit the last one—but it was never my style, so instead I just felt increasingly frustrated. I was sick of joining ‘movements’ to quickly become nothing more than a ‘clicktavist’, and was not prepared to turn my back and sink into a state of total apathy. I felt extremely powerless and that made me angry. ‘Rachael!’ I heard someone call my name. It was Jim Dixon, an old friend and fellow graduate of the University of Bristol’s MA in Historical Archaeology.
Hilbert and his famous problem
Authors: Copeland Jack
Published: November 2020

In 1936 mathematics was changing profoundly, thanks to Turing and his fellow revolutionaries Gödel and Church. Older views about the nature of mathematics, such as those powerfully advocated by the great mathematician David Hilbert, were being swept away, and simultaneously the foundations for the modern computer era were being laid. These three revolutionaries were also catching the first glimpses of an exciting new world—the hitherto unknown and unimagined mathematical territory that lies beyond the computable. In the 1930s a group of iconoclastic mathematicians and logicians launched the field that we now call theoretical computer science. These pioneers embarked on an investigation to spell out the meaning and limits of computation. Pre-eminent among them were Alan Turing, Kurt Gödel, and Alonzo Church. These three men are pivotal figures in the story of modern science, and it is probably true to say that, even today, their role in the history of science is underappreciated. The theoretical work that they carried out in the 1930s laid the foundations for the computer revolution, and the computer revolution in turn fuelled the rocketing expansion of scientific knowledge that characterizes modern times. Previously undreamed of number-crunching power was soon boosting all fields of scientific enquiry, thanks in large part to these seminal investigations. Yet, at the time, Turing, Gödel, and Church would have thought of themselves as working in a most abstract field, far flung from practical computing. Their concern was with the very foundations of mathematics. Kurt Gödel (Fig. 7.1), a taciturn 25-year-old mathematician from Vienna University, ushered in a new era in mathematics with his 1931 theorem that arithmetic is incomplete. In a sentence, what Gödel showed is that more is true in mathematics than can be formally proved. This sensational result shocked, and even angered, some mathematicians. It was thought that everything that matters ought to be provable, because only rigorous proof by transparent and obvious rules brings certainty.
At Bletchley Park
Authors: Copeland Jack
Published: November 2020

This chapter summarizes Turing’s principal achievements at Bletchley Park and assesses his impact on the course of the Second World War. On the first day of the war, at the beginning of September 1939, Turing took up residence at Bletchley Park, the ugly Victorian mansion in Buckinghamshire that served as the wartime HQ of Britain’s military codebreakers (Fig. 9.1). There Turing was a key player in the battle to decrypt the coded messages generated by Enigma, the German forces’ typewriter-like cipher machine. Germany’s army, air force, and navy transmitted many thousands of coded messages each day during the Second World War. These ranged from top-level signals, such as detailed situation reports prepared by generals at the battlefronts and orders signed by Hitler himself, down to the important minutiae of war such as weather reports and inventories of the contents of supply ships. Thanks to Turing and his fellow codebreakers, much of this information ended up in Allied hands—sometimes within an hour or two of its being transmitted. The faster the messages could be broken, the fresher the intelligence that they contained, and on at least one occasion the English translation of an intercepted Enigma message was being read at the British Admiralty less than 15 minutes after the Germans had transmitted it. Turing pitted machine against machine. Building on pre-war work by the legendary Polish codebreaker Marian Rejewski, Turing invented the Enigma-cracking ‘bombes’ that quickly turned Bletchley Park from a country house accommodating a small group of thirty or so codebreakers into a vast codebreaking factory. There were approximately 200 bombes at Bletchley Park and its surrounding outstations by the end of the war. As early as 1943 Turing’s machines were cracking a staggering total of 84,000 Enigma messages each month—two messages every minute. Chapter 12 describes the bombes and explains how they worked. Turing also undertook, single-handedly at first, a 20-month struggle to crack the especially secure form of Enigma used by the North Atlantic U-boats. With his group he first broke into the current messages transmitted between the submarines and their bases during June 1941, the very month when Winston Churchill’s advisors were warning him that the wholesale sinkings in the North Atlantic would soon tip Britain into defeat by starvation.