bluuebunny/crossref_metadata_2025 huggingface dataset:
Analgesia and Anaesthesia
Authors: Gupta Pawan
Published: November 2020

Seventy per cent of patients who present to the ED have pain as their main complaint—and most of the time as a sign of injury or inflammation. Therefore, early assessment by scoring at the point of triage and offering the appropriate analgesia are the first steps towards the management of such patients. The College of Emergency Medicine guidelines suggest that at least 98% of patients in severe pain (pain score of 7–10) should be offered appropriate analgesia within 60min of arrival, or triage, whichever is earlier. In 90% of these patients, the status of pain should be re-evaluated within 60min of receiving the first dose of the analgesic. Despite this clear-cut standard and the availability of a wide variety of analgesics, achieving such a target remains, occasionally, elusive. It must also be realized that a positive experience for the patient largely depends on relief of pain as early as possible. Consequently, one of the primary areas for a new FY1 to focus on is the pain management. Remember it is simple and straightforward in most circumstances. GA may be required in the ED for various clinical indications, for example, cardioversion, facial trauma or burns, and acute respiratory failure (such as in asthma). In an emergency situation it may be a challenging procedure even for an experienced anaesthetist and could be dangerous for the patients. An FY1/2 will never be expected to perform this, but it is important to know when to call for help when the situation demands. Local anaesthesia is widely used in the ED, and is one of the skills foundation trainees learn in the early days. It is comparatively safe if the doctor is aware of how to perform the procedure and the upper limit of the dose for a particular patient. Finally, conscious sedation is also widely used in the ED for reducing fractures and/or dislocations and minor operations. However, it carries the same risks as GA and should be carried out by a doctor who is trained in the procedure as well as in resuscitation. A risk assessment should be performed as a patient with high risks (previous cardiac or respiratory diseases) must be sedated with extreme caution.
Surgery
Authors: Gupta Pawan
Published: November 2020

Among surgical patients presenting to the ED, abdominal pain is the most common complaint, comprising 10% of ED visits. Evaluation of such patients in the ED is often challenging for a variety of reasons, such as the variability in the description of the perception of pain in individual patients, variable and changing physical findings with time, and life-threatening conditions presenting as seemingly benign symptoms. I always advise inexperienced doctors working in the ED to bear in mind seven time bombs that may be ‘sitting inside’ every adult patient’s abdomen who presents with abdominal pain. Patients who are discharged, but in whom one of these diagnoses was missed, will be blue-lighted back to the department dead. Therefore, before discharging a patient presenting with acute abdomen pain, all such conditions as listed below must be excluded beyond reasonable doubt. These conditions are: • Ruptured AAA • Hollow viscus perforation • Mesenteric ischaemia • Ruptured ectopic pregnancy • Acute pancreatitis • Intestinal obstruction • Acute myocardial infarction. Acute (inferior) myocardial infarction may present as upper abdominal pain and cannot afford to be missed. Patients >50 years presenting with abdominal pain must have an ECG in the ED, not only for detecting acute myocardial infarction, but for other associated cardiac problems precipitating an abdominal catastrophe. Elderly patients are more likely to have life-threatening conditions such as a ruptured AAA, mesenteric ischaemia, peptic perforation, and diverticulitis. Atypical presentations and rapid progression of these diseases, coupled with decreased diagnostic accuracy, may increase the risk of mortality in elderly patients. The only way to avoid the above is, as importantly as in other parts of medicine, by taking an accurate history, performing a thorough full clinical examination, arranging appropriate investigations rapidly, and making the correct decisions as to whether or not urgent surgery is required. Even with advanced imaging techniques, a good understanding of background clinical information is of utmost importance for accurate interpretation of imaging findings. This chapter includes questions on acute abdominal emergencies to give the reader an insight into the latest management strategies for these situations.
Ultrasound in cardiology —state of the art
Authors: Pinto Fausto J.
Published: November 2020

Echocardiography represents the most widely used diagnostic tool in cardiology. From its beginnings, in 1953, when Professor Inge Edler first used it in Lund, Sweden, there always was a clinical question underlying its use and development. This might be one of the main reasons why echocardiography has always been one of the most popular diagnostic methods to be used clinically and several authors have named it as the fastest growing technique in cardiology. In fact, there are a variety of areas where echocardiography has proven to be fundamental not only for clinical orientation but also for significantly increasing the understanding of the underlying pathophysiology of the disease process. The other important aspect is the fact that, at the same time, significant technological developments have occurred that have made it possible to develop adequate transducers able to accompany the clinical questions. Some of the main features and contributions of echocardiography in different clinical conditions can be summarized as follows. Heart failure remains one of the main killers in the developed world with its prevalence increasing worldwide mainly as the result of coronary artery disease (CAD), responsible for almost two-thirds of cases of left ventricular (LV) dysfunction. Echocardiography has played a major role in the understanding of the different mechanisms involved in the development of the different types of heart failure. In addition, it has helped to monitor and develop new therapeutic targets and strategies in heart failure. LV function represents the most important prognostic indicator in patients with heart disease regardless of their aetiology. Echocardiography has been the main diagnostic tool to assess how much systolic and diastolic function are involved in the mechanism of heart failure in a particular patient. Regarding systolic function, echocardiography can provide different measurements that contribute to a more objective assessment of function, including: global and regional function, degree of ventricular remodelling, contractile reserve, presence of ischaemia and/or viability, particularly in patients post-acute coronary syndromes or post-myocardial revascularization, and the concomitant presence of valvular heart disease, which may significantly impact on the assessment of LV function (particularly the presence of significant volume overload, such as in mitral and/or aortic regurgitation).
The development of ultrasound in obstetrics and gynaecology in Sweden
Authors: Maršál Karel , Sundén Bertil
Published: November 2020

In the field of obstetrics, the advent of diagnostic ultrasound was most welcome because of the obvious lack of a non-invasive method providing information on the fetus in utero. The subsequent very fast and widespread use of ultrasound in clinical obstetrics was vindication that the method fulfilled the expectations and that it literally ‘opened a window into the uterus’. Ultrasound enabled direct examinations of fetal anatomy, measurements of fetal size and growth, and recording of intrauterine activities. Nowadays, 97 % of all pregnant women in Sweden undergo at least one ultrasound examination during their pregnancy. The early positive results reported from the application of ultrasound in cardiology and neurosurgery at Lund University elicited interest to test the method on pregnant women at the Department of Obstetrics and Gynecology in Lund. In 1957, Alf Sjövall, then professor in obstetrics and gynaecology, discussed over a lunch-table with neurosurgeon Lars Leksell his very first experience of diagnosing subdural hematoma using ultrasound. Professor Sjövall asked then Bertil Sundén, who worked at his department, to investigate early pregnancies with the Krautkrämer echoscope belonging to Leksell. The aim was to examine whether it would be possible to detect echoes from the fetus in early pregnancies and to differentiate it from myomatous enlargements of the uterus and from ovarian tumours. The Krautkrämer echoscope offered only an A-mode display of ultrasound signals so no tangible results were obtained as the origin of the echoes could not be identified. At that time, it was unknown whether or not ultrasound might have any harmful effects on embryonic tissue and therefore these first investigations in early pregnancies were done on patients admitted for interruption of pregnancy. After that Ian Donald published the first description of an echoscope generating a two dimensional display in 1958, Bertil Sundén went on a three-week visit to Professor Donald in Glasgow. There he met electronic engineer Tom G. Brown, employed by Smiths Industrial Division in Glasgow, who had built Donald’s machine. During his stay in Glasgow Sundén performed several investigations on obstetric and gynaecological patients using Brown’s equipment that was the only one of its type.
The development of ultrasound in vascular disease in Sweden
Authors: Jogestrand Tomas , Thulesius Olav
Published: November 2020

The famous British scientist Sir Cyril A. Clarke in 1975 wrote the introduction for a new book, Arteries and Veins , with the following words: . . . In spite of all advances, mortality remains a steady 100 per cent and it is disorders of the arteries and veins which claim the majority of us. we sclerose, we clot, arrhythmias hit us, or our tubing wears out. By way of consolation, however, more of us now go the way of all flesh properly diagnosed and there are many ways of cheating the ancient enemy. . . . Clark at the time did not realize what advances were ahead of him, and the book he introduced with these dark lines included a chapter by R.G. Gosling and D.H. King which described a new promising technique of ultrasound angiography. Cyril Clark himself died at the age of 93! Blood flow measurements during resting conditions fail to detect any reduction of volume flow in patients with occlusive vascular disease, therefore for quantitative evaluation of the functional capacity of the peripheral circulation various functional tests implying increased circulatory demands needed to be introduced. The most useful clinical information could be obtained from peak-flow values after a period of obstruction and exercise followed by volume plethysmographic measurements of blood flow. Olav Thulesius introduced a foot ergometer in 1963 which allowed detection of maximal blood flow after graded muscular exercise. Its use was complicated and time-consuming when applied in conjunction with blood flow measurements with a water-filled volume plethysmograph. Therefore a faster and easier method for determination of peripheral blood flow was desirable. In 1967, the ultrasound scanning method for the detection of arterial blood flow signals in the diagnosis of fetal life during pregnancy was introduced in Sweden. This same principle became the method for detecting blood flow in peripheral blood vessels. The method used was a hand-held instrument which included two piezoelectric elements, one to transmit ultrasound signals and the other to receive the returning echoes back-scattered from the blood vessels. The instrument used for the detection of peripheral blood flow was the same as that for the detection of the fetal blood flow in pregnancy.
Fluorescence principles and measurement
Authors: Szabo Arthur G.
Published: November 2020

Fluorescence spectrometry is the most extensively used optical spectroscopic method in analytical measurement and scientific investigation. During the past five years more than 60000 scientific articles have been published in which fluorescence spectroscopy has been used. The large number of applications ranges from the analytical determination of trace metals in the environment to pH measurements in whole cells under physiological conditions. In the scientific research laboratory, fluorescence spectroscopy is being used or applied to study the fundamental physical processes of molecules; structure-function relationships and interactions of biomolecules such as proteins and nucleic acids; structures and activity within whole cells using such instrumentation as confocal microscopy; and DNA sequencing in genomic characterization. In analytical applications the use of fluorescence is dominant in clinical laboratories where fluorescence immunoassays have largely replaced radioimmunoassay techniques. There are two main reasons for this extensive use of fluorescence spectroscopy. Foremost is the high level of sensitivity and wide dynamic range that can be achieved. There are a large number of laboratories that have reported single molecule detection. Secondly, the instrumentation required is convenient and for most purposes can be purchased at a modest cost. While improvements and advances continue to be reported fluorescence instrumentation has reached a high level of maturity. A review of the physical principles of the fluorescence phenomenon permits one to understand the origins of the information content that fluorescence measurements can provide. A molecule absorbs electromagnetic radiation through a quantum mechanical process where the molecule is transformed from a ‘ground’ state to an ‘excited’ state. The energy of the absorbed photon of light corresponds to the energy difference between these two states. In the case of light in the ultraviolet and visible spectral range of 200 nm to 800 nm that corresponds to energies of 143 to 35.8 kcal mol-1. The absorption of light results in an electronic transition in the atom or molecule. In atoms this involves the promotion of an electron from an outer shell orbital to an empty orbital of higher energy.
Introduction to circular dichroism
Authors: Rodger Alison , Ismail Matthew A.
Published: November 2020

Circular dichroism (CD) is the ideal technique for studying chiral molecules in solution. It is uniquely sensitive to the asymmetry of the system. These features make it particularly attractive for biological systems. CD is by definition the difference in absorption, A, of left and right circularly polarized light (CPL): . . . CD = Ae − Ar . . . . . . 1 . . . CPL has the electric field vector of the electromagnetic radiation retaining constant magnitude in time but tracing out a helix about the propagation direction. Following the optics convention we take the tip of the electric field vector of right CPL to trace out a right-handed helix in space at any instant of time (1, 2). CD spectra can in principle be measured with any frequency of electromagnetic radiation. In practice, most CD spectroscopy involves the ultraviolet-visible (UV-visible) regions of the spectrum and electronic transitions, though increasing progress is being made with measuring the CD spectra of vibrational transitions using infrared radiation. We shall limit our consideration to electronic CD spectroscopy since the practical considerations for vibrational CD differ from those for electronic CD. For randomly oriented samples, such as solutions, a net CD signal will only be observed for chiral molecules (ones that cannot be superposed on their mirror images (3)). Oriented samples of achiral molecules, such as crystals, will also give a CD spectrum unless the optical axis of the sample aligns with the propagation direction of the radiation. However, such spectra are seldom useful. CD is now a routine tool in many laboratories. The most common applications include proving that a chiral molecule has indeed been synthesized or resolved into pure enantiomers and probing the structure of biological macromolecules, in particular determining the α-helical content of proteins. Figure 3 gives an example of a CD spectrum. The key points to remember are that a CD signal is observed only at wavelengths where the sample absorbs radiation, i.e. under absorption bands, and the signal may be positive or negative depending on the handedness of the molecules in the sample and the transition being studied.
Quantitative determination of equilibrium binding isotherms for multiple ligand-macromolecule interactions using spectroscopic methods
Authors: Bujalowski Wlodzimierz , Jezewska Maria J.
Published: November 2020

Thermodynamic studies provide information that is necessary in order to understand the forces that drive the formation of ligand-macromolecule complexes. Knowledge of the energetics of these interactions is also indispensable for characterization of functionally important structural changes that occur within the studied complexes. Quantitative examination of the equilibrium interactions are designed to provide the answers to the questions: What is the stoichiometry of the formed complexes? How strong or how specific are the interactions? Are there any cooperative interactions among the binding sites and/or the bound ligand molecules? Are the binding sites intrinsically heterogeneous? What are the molecular forces involved in the formation of the studied complexes, or, in other words, how do the equilibrium binding and kinetic parameters depend on solution variables (temperature, pressure, pH, salt concentration, etc.)? Equilibrium isotherms for the binding of a ligand to a macromolecule represent the relationship between the degree of ligand binding (moles of ligands bound per mole of a macromolecule) and the free ligand concentration. A true thermodynamic binding isotherm is model-independent and reflects only this relationship. Only then, when such an isotherm is obtained, can one proceed to extract physically meaningful interaction parameters that characterize the free energies of interaction. This is accomplished by comparing the experimental isotherms to theoretical predictions based on specific binding models that incorporate known molecular aspects, such as intrinsic binding constants, cooperativity parameters, allosteric equilibrium constants, discrete character of the binding sites or overlap of potential binding sites, etc. (see below). Any method used to quantitatively study ligand binding to a macromolecule must relate the extent of the complex formation to the free ligand concentration in solution. Numerous techniques have been developed to study equilibrium properties of specific and non-specific ligand-macromolecule interactions in which binding is directly monitored, including equilibrium dialysis, ultrafiltration, column chromatography, filter binding assay and gel electrophoresis (1-6). These direct methods are very straightforward; however, they are usually time consuming and some, like filter binding or gel shift assays, are non-equilibrium techniques which require many controls before the reliable equilibrium binding data can be obtained.
Loadstones and Earths
Authors: Wothers Peter
Published: November 2020

Jöns Jacob Berzelius (1779–1848), discoverer of the elements selenium, thorium, cerium, and silicon and deviser of the chemical symbols we use today, was one of the last in a long list of Swedish mineralogists and chemists active during the eighteenth century. Berzelius himself regarded one of his predecessors, Axel Fredrik Cronstedt (1722–65), as the founder of chemical mineralogy. We met Cronstedt in Chapter 2 as the discoverer of the element nickel, isolated from the ore kupfernickel. But another of Cronstedt’s achievements was perhaps of even greater significance: his development of a classification of minerals based not on their physical appearances, as had been common up to this time, but on their chemical compositions. He first published his scheme anonymously in Swedish in 1758, but it was later translated into English as An Essay towards a System of Mineralogy. Cronstedt recognized four general classes of minerals: earths, bitumens, salts, and metals. As their name suggests, the bitumens were flammable substances that might dissolve in oil but not in water. The main difference between the salts and the earths was that the former, which included the ‘alcaline mineral salt’ natron, could be dissolved in water and recrystallized from it. The earths he defined as ‘those substances which are not ductile, are mostly indissoluble in water or oil, and preserve their constitution in a strong heat’. Cronstedt initially recognized nine different classes of earth. By the time of Torbern Bergman (1735–84), these had been reduced to five which ‘cannot be derived from each other or from anything simpler’. Lavoisier and his collaborators included these five in their great work on nomenclature even though they suspected that, like soda and potash, they were most likely not simple substances, but species that contained new metals. In the 1788 English translation of the nomenclature these were called silice, alumina, barytes, lime, and magnesia. The first two eventually, in the early nineteenth century, yielded the elements silicon and aluminium. The word ‘silicon’ derives from the Latin ‘silex’ (meaning ‘flint’—a form of silicon dioxide), with the ending ‘-on’ reflecting its resemblance to the other non-metals carbon and boron.
Total Landscapes (250 BC to the Early Roman Period)
Authors: Bradley Richard , Haselgrove Colin , Vander Linden Marc , Webley Leo
Published: November 2020

By the late first century BC, most of north-west Europe had been incorporated into the Roman Empire or had fallen under its shadow. This has profoundly affected how the late Iron Age is perceived and studied. Being able to view peoples and places through written sources and coin inscriptions means that the archaeology of the period is often approached very differently to those discussed in previous chapters, with greater emphasis on historical events and causality. The chronology encourages this. Late La Tène sites on the Continent can now be dated to within a generation or so, anchored by a growing number of dendrochronological fixed points (Kaenel 2006; Durost and Lambert 2007), although similar precision is rarely attainable in northern Europe or in Ireland and northern Britain, which rely largely on radiocarbon dating. The prevailing narrative for the late Iron Age in central Europe, Gaul, and southern Britain—essentially the areas that later became part of the Roman empire—is one of increasing hierarchy, social complexity, political centralization, urbanization, and economic development. These changes are seen as bound up with increasing contact with the Mediterranean world, leading up to the Roman conquests of the first centuries BC and AD. This is contrasted with the situation in northern Britain, Ireland, and ‘Germanic’ northern Europe, which are assumed to have been more tradition-bound and resistant to change. As we shall see, recent excavations do not necessarily contradict this narrative, but they do suggest that the picture is far more complex. Not all developments can be fitted into the story of growing social complexity, whilst to assume that Roman expansion was the most important factor at work at this period is to see events through the eyes of Classical writers (Bradley 2007). It is important to understand late Iron Age societies in their own terms, rather than just as precursors to provincial Roman societies. Many influential approaches to the period—from core–periphery models to the current emphasis on the agency of client rulers (Creighton 2000)—suffer from teleology as a result of having been constructed with half an eye to explaining the pattern of Roman expansion.
A place in the sun—occupational groups’ professionalization projects and other status and influence ambitions
Authors: Alvesson Mats
Published: November 2020

In an age of high—even galloping—expectations of better working and living conditions, higher status, and an active role in a ‘knowledge-intensive society’, it is hardly surprising that many employees and occupational groups want to advance their positions. They want to have the status, attractive working conditions, and influence that they feel they deserve. There are participants in various fields—researchers, popular authors, teachers, trade unions, and representatives of various professions—who are keen to launch ideas about the importance of their specific occupation or field of knowledge, and what the general public, organizations, and clients would gain if that occupation or field of knowledge had greater influence and status. Many of these attempts to advance positions take the form of launching and reinforcing such occupations by turning them into professions. Increased professionalization is broadly viewed as a good thing, in the interest of the specific occupation concerned as well as for society as a whole. This applies particularly to occupations in the public sector, where the achievements are often hard to determine, as previously mentioned. The absence or weakness of the market as a disciplinary mechanism—showing often more interest in what is delivered (or believed to be delivered) than in formal qualification and authorization of groups—also leads to a direction of energy into professionalization projects. Scoring high on signs of being a ‘profession’ becomes an indicator of success. Exceptions include such occupations as engineers, managers, consultants, and advertising experts are in most countries not certified or professionalized in any strict sense—and when they are targeted for certification efforts this is attributed little significance (Alexius, 2007). (Chartered accountants are a somewhat different matter.) However, generally, there is an increasing focus on regulating which occupational groups are to be entitled to do what, by applying statutory provisions and formal requirements for education and training. As is the case with many other popular concepts, the term ‘profession’ is used in different ways. But the general notion is that a profession is better than a ‘non-profession’ and professionalization is typically viewed as a way to bring an occupation forwards and upwards in the battle for status, respect, influence, and attractive job positions.
The Curious Incident of the Dog in the Airship
Authors: Öhrström Lars
Published: November 2020

Joseph Späh had to feed his dog; nothing strange about that. The problem was that Ulla, an Alsatian, was mostly confined to the freight room—off limits to passengers. Had everything gone according to schedule, this would not have been an issue either, except for gruff remarks from crewmen not appreciating the needs of this canine friend and co-worker in Späh’s stage act. But this flight did not go according to plan, and Späh’s frequent visits to the rear of the Hindenburg would give him problems in the years to come. The US Department of Energy, and its counterparts in Europe and Japan, are currently spending billions on developing the use of hydrogen for future energy applications—for example, as a fuel for cars and buses. The main advantage is the clean combustion of this fuel: two molecules of hydrogen gas will combine with one molecule of oxygen and give two molecules of water. The future belongs, perhaps, to the ‘hydrogen economy’, but unfortunately for its proponents, the popular history of hydrogen as a fuel is bound up with the tragedy of the Hindenburg. We will get back to Joseph Späh’s poor dog in a while, but for now ponder the fact that over the dog, and above everyone else aboard the comfortable and luxurious Hindenburg , there were huge ‘bags’ filled with hydrogen—the lightest of all the elements, with only one proton and one electron. It has the lowest density of any gas, and is formed by two hydrogen atoms combined together via a single chemical bond, made by sharing the two negatively charged electrons between the two positively charged nuclei. This H2 gas had carried the world’s largest airship from Frankfurt to Lakehurst outside New York, and before that on successful tours all over the globe during the preceding year. These days, we tend to wonder how people could even contemplate the idea of travelling around in what can be described as a flying bomb.
Biopiracy: Th e Curse of the Nutmeg
Authors: Öhrström Lars
Published: November 2020

Governments and private donors often try to control public research by handing out very specific grants, expecting closely related output such as patents, new companies, and inventions in the specified directions. Researchers, in general, vehemently oppose such policies, arguing that much better patents, new companies, and inventions will result if they are left to their own devices, making decisions on where to use their spatulas, syringes, and microscopes. Grant applications are therefore sometimes written using an obedient language adhering to whatever policies and applications are in vogue at the time, but with a more or less concealed plan B containing the real scientific questions we think should be in focus. This is by no means a new phenomenon, and one of the most flagrant misuses of a research grant must have been that of Captain Henry Hudson in 1609. Issued with a ship, men, and provisions by the Dutch East India Company (VOC, Vereenigde Oost-Indische Compagnie), the agreed research plan was to explore a route to the Indies by sailing north of Scandinavia and Russia—the so-called north-east passage. He did make an attempt, but somewhere east of Scandinavia’s northernmost point, close to North Cape, he had a better idea and turned his ship west. He crossed the Atlantic and, among other things, explored what was to be named the Hudson River. This gave the Dutch Republic a claim to a large island called Manna-hata by the local population, one suspects much to the regret of Hudson’s English compatriots. This urge to go east was partly driven by the enormous profits there were to be made in the spice trade—both on returning home, and on shipping items such as cloves, pepper, and nutmeg within Asia. In a way one can (being a bit chemo-chauvinistic) regard the spice trade as a chemical trade, as a number of very specific molecules make up our sensation of spices compared to the experience of eating rice for example, another important part of the East-Indian trade. To a first approximation, rice is a mixture of very big molecules such as carbohydrates and proteins, and factors like texture and water content are also important for the overall eating experience.
Soil and the City
Authors: Bardgett Richard
Published: November 2020

I have spent most of my living and working life in the countryside, surrounded by open fields, woodlands and hills, and in close contact with the soil. I recently changed my job and moved to the University of Manchester, which is in the centre of one of the largest cities in England. Because of this move my contact with soil is much less; in fact, as I walk each morning to my office, there is hardly a handful of soil to be seen. But is this really true of the whole city? Concrete, asphalt, and bricks certainly seal much of the ground in Manchester, as in most cities and towns. But soil is in abundance: it lies beneath the many small gardens, flower beds, road and railway verges, parks, sports grounds, school playing fields, and allotments of the city. In fact, it has been estimated that almost a quarter of the land in English cities is covered by gardens, and in the United States, lawns cover three times as much area as does corn. As I write, I am on a train leaving central London from Waterloo Station, and despite the overwhelming dominance of concrete and bricks, I can see scattered around many small gardens, trees, flowerpots and window boxes, overgrown verges on the railway line, small parks and playing fields for children, football pitches, grassy plots and flower beds alongside roadways and pavements, and small green spaces with growing shrubs outside office blocks and apartments. The city is surprisingly green and beneath this green is soil. Throughout the world, more and more people are moving to cities: in 1800 only 2 per cent of the world’s population was urbanized, whereas now more than half of the global human population live in towns and cities, and this number grows by about 180,000 people every day. This expansion has been especially rapid in recent years.
Traditional direct phasing procedures
Authors: Giacovazzo Carmelo
Published: November 2020

Which phasing methods can be included in the category direct methods, and which require a different appellation? Originally, direct phasing was associated with those approaches which were able to derive phases directly from the diffraction moduli, without passing through deconvolution of the Patterson function. Since a Patterson map provides interatomic distances, and therefore lies in ‘direct space’, direct methods were also referred to as reciprocal space methods, and Patterson techniques as real-space methods. Historically, direct methods use 3-,4-, . . . , n-phase invariants and 1-2-, . . . phase seminvariants via the tangent formula or its modified algorithms. Since the 1950s, about a half a century of scientific effort has fallen under the above definition. Such approaches are classified here as traditional direct methods. Today, the situation is more ambiguous, because: (i) modern direct methods programs involve steps operating both in reciprocal space and in direct space, the latter mainly devoted to phase extension and refinement (see Chapter 8); (ii) in the past decade, new phasing methods for crystal structure solution (see Chapter 9) have been developed, based on the properties of Fourier transforms, which again work both in direct and in reciprocal space. Should they therefore be considered to be outside the direct methods category or not? Our choice is as follows. Direct methods are all of the approaches which allow us to derive phases from diffraction amplitudes, without passing through a Patterson function deconvolution. Thus, we also include in this category, charge flipping and VLD (vive la difference), here classified as non-traditional direct methods; their description is postponed to Chapter 9. In accordance with the above assumptions, in this chapter we will shortly illustrate traditional direct phasing procedures, with particular reference to those which are current and in regular use today: mainly the tangent procedures (see Section 6.2) and the cosine least squares technique, which is the basic tool of the shake and Bake method (see Section 6.4).
Joint probability distribution functions when a model is available: Fourier syntheses
Authors: Giacovazzo Carmelo
Published: November 2020

The title of this chapter may seem a little strange; it relates Fourier syntheses, an algebraic method for calculating electron densities, to the joint probability distribution functions of structure factors, which are devoted to the probabilistic estimate of s.i.s and s.s.s. We will see that the two topics are strictly related, and that optimization of the Fourier syntheses requires previous knowledge and the use of joint probability distributions. The distributions used in Chapters 4 to 6 are able to estimate s.i. or s.s. by exploiting the information contained in the experimental diffraction moduli of the target structure (the structure one wants to phase). An important tool for such distributions are the theories of neighbourhoods and of representations, which allow us to arrange, for each invariant or seminvariant Φ, the set of amplitudes in a sequence of shells, each contained within the subsequent shell, with the property that any s.i. or s.s. may be estimated via the magnitudes constituting any shell. The resulting conditional distributions were of the type, . . . P(Φ| {R}), (7.1) . . . where {R} represents the chosen phasing shell for the observed magnitudes. The more information contained within the set of observed moduli {R}, the better will be the Φ estimate. By definition, conditional distributions (7.1) cannot change during the phasing process because prior information (i.e. the observed moduli) does not change; equation (7.1) maintains the same identical algebraic form. However, during any phasing process, various model structures progressively become available, with different degrees of correlation with the target structure. Such models are a source of supplementary information (e.g. the current model phases) which, in principle, can be exploited during the phasing procedure. If this observation is accepted, the method of joint probability distribution, as described so far, should be suitably modified. In a symbolic way, we should look for deriving conditional distributions . . . P (Φ| {R}, {Rp}) , (7.2) . . . rather than (7.1), where {Rp} represents a suitable subset of the amplitudes of the model structure factors. Such an approach modifies the traditional phasing strategy described in the preceding chapters; indeed, the set {Rp} will change during the phasing process in conjunction with the model changes, which will continuously modify the probabilities (7.2).
Can You Compute?
Authors: Bentley Peter J.
Published: November 2020

Created by pioneering mathematicians and engineers during times of political unrest and war, computers are more than electronic machines. Underneath the myriad complicated circuits and software glows a mathematical purity that is simplicity itself. The maths at the root of computers illuminates the nature of reality itself. Today explorers of the impossible still compete to find the limits in our universe. With a revolution in mathematics and technology and a million dollars at stake, who can blame them? . . . It was 1926 and the General Strike was taking place in England because of disputes over coal miners’ pay. There were no buses or trains running. Fourteen-year-old Alan Turing was supposed to be starting at a grand boarding school: Sherborne in Dorset. Yet he was living in Southampton, some sixty miles away. Many children would have simply waited for the ten-day strike to finish and have a longer holiday. Not Turing. He got on his bike and began cycling. It took him two days, with a stay in a little hotel halfway, but young Turing made it to his new school on time. Turing’s independence may have stemmed from the fact that he and his older brother John had seen little of their parents while growing up. Both parents were based in India, but decided their children should be educated in England. The boys were left with friends of the family in England until their father retired and returned in 1926—just as Turing made his way to the new school. It was an impressive start, but Alan Turing didn’t do very well at his new school—he never had in any previous school. His handwriting was terrible, his written English poor. His English teacher said, ‘I can forgive his writing, though it is the worst I have ever seen, and I try to view tolerantly his unswerving inexactitude and slipshod, dirty, work . . .’ The Latin teacher was not much more approving. ‘He is ludicrously behind.’ The problem was that Turing didn’t pay attention to the curriculum being taught. Instead he spent more time following his own interests.
Burns Night: Combustion
Authors: Atkins Peter
Published: November 2020

Burning, more formally combustion, denotes burning in oxygen and more commonly in air (which is 20 per cent oxygen). Combustion is a special case of a more general term, ‘oxidation’, which originally meant reaction with oxygen, not necessarily accompanied by a flame. The rusting of iron is also an oxidation, but we don’t normally think of it as a combustion because no flame is involved. Oxidation now has a much broader meaning than reaction with oxygen, as I shall unfold in Reaction 5. For now, I shall stick to combustion itself. To achieve combustion, we take a fuel, which might be the methane, CH4, 1, of natural gas or one of the heavier hydrocarbons, such as octane, C8H18, 2, that we use in internal combustion engines, mix it with air, and ignite it. The outcome of the complete combustion of any hydro-carbon is carbon dioxide and water but incomplete combustion can result in carbon monoxide and various fragments of the original hydrocarbon molecule. All combustions are ‘exothermic’, meaning that they release a lot of energy as heat into the surroundings. We use that energy for warmth or for driving machinery. Another example of an exothermic combustion is provided by the metal magnesium, which gives an intense white light as well as heat when it burns in air. A part of the vigour of this reaction is due to the fact that magnesium reacts not only with oxygen but also with nitrogen, the major component of air. You should be getting a glimpse of the broader significance of the term ‘oxidation’ in the sense that the reaction need not involve oxygen; in magnesium’s case, nitrogen can replace oxygen in the reaction. Magnesium foil was used in old-fashioned photographic flashes and in fireworks. The latter now mostly use finely powdered aluminium, which is much cheaper than magnesium and reacts in much the same way. In what follows you could easily replace aluminium with magnesium if you want to think fireworks. For the whole of the following discussion you need to be familiar with oxygen, O2, 3, a peculiar molecule in several respects.
Electric Occurrence: Electrolysis
Authors: Atkins Peter
Published: November 2020

Electrolysis makes use of electric currents, a stream of electrons, to bring about chemical change. It puts electricity to work by using it to break or form bonds by forcing electrons on to molecules or sucking electrons out of them. Electrolysis is an application of the redox processes I described in Reaction 5, where I showed that reduction is the gain of electrons and that oxidation is their loss. All that happens in electrolysis is the use of an external supply of electrons from a battery or other direct-current (DC) source to push them on to a species and so bring about its reduction, or the use of the electron-sucking power of a battery to remove them from a species to bring about its oxidation. Electrolysis, in other words, is electrically driven reduction and oxidation. In fact, the process is rather broader than just forcing species to accept or give up electrons because, as I have hinted, molecules might respond to the change in their number of electrons by discarding or rearranging atoms. For instance, when water is electrolysed, the H–O bonds of the H2O molecules are broken and hydrogen and oxygen gases are formed. When an electric current is passed through molten common salt (sodium chloride, NaCl), metallic sodium and gaseous chlorine, Cl2, are formed. Electrolysis is a major technology in the chemical industry, for among other applications it is used to make chlorine, to purify copper, and to extract aluminium. To bring about electrolysis, two metal or graphite rods, the ‘electrodes’, are inserted into the molten substance or solution and connected to a DC electrical supply. The electrons that form the electric current enter the substance through one electrode (the ‘cathode’) and leave it through the other electrode (the ‘anode’). A molecule or ion close to the cathode is forced to collect one or more electrons from that electrode and be reduced. A molecule or ion close to the anode is forced to release them to that electrode and thereby become oxidized. A reasonably simple first example is the purification of copper.
The Generation Game: Electrochemistry
Authors: Atkins Peter
Published: November 2020

You already know, if you have read Reaction 6, that an electric current is a stream of electrons. If you have also read the section on redox reactions (Reaction 5), which you should, in preparation for this account, then you will also know that in a redox reaction electrons are transferred from one species to another. Although it is now far too late, had you had that information 150 or so years ago, then you might have realized that if those species were at the opposite ends of a piece of wire, the transfer of electrons would then take place in the form of an electric current travelling along the wire and you would have invented the electric battery. All the batteries that are used to generate electricity and drive portable electrical and electronic equipment, from torches, drills, phones, music players, laptops, through to electric vehicles, are driven by this kind of chemically produced flow of electrons. One of the earliest devices for producing a steady electric current was the ‘Daniell cell’, which was invented in 1836 by John Daniell (1790–1845) of King’s College, London in response to the demand in the nineteenth century of the then emerging technology of telecommunication for a steady, cheap source of electricity. I have already touched on the underlying reaction when I explained what happens when a piece of zinc, Zn, is dropped into a solution of copper sulfate (Reaction 5), and this section builds on that account. In that reaction copper is deposited on the zinc and the copper sulfate solution gradually loses its colour as blue Cu2+ ions are replaced by colourless Zn2+ ions. As this reaction takes place, electrons hop from the zinc metal onto Cu2+ ions nearby in the solution. If we were to stand there watching, we would see electrons snapping across from the zinc to the Cu2+ ions wherever the latter came within striking distance of the zinc surface. There would be electron transfer, but no net current of electricity. Daniell did what I outlined in the opening paragraph: he separated the zinc metal and copper ions, so that electrons released by zinc had to travel through an external wire to get to the Cu2+ ions.
Chronology
Authors: Harding Dennis
Published: November 2020

Hillforts are conventionally regarded as a phenomenon of the Late Bronze Age and Iron Age of temperate Europe, with some sites being constructed or reoccupied in the post-Roman Iron Age or Early Medieval period. In broad chronological terms, 1000 BC to AD 1000 covers the two millennia of the ‘long Iron Age’ in which hillforts are a major field monument. The concept of enclosure nevertheless has a much longer ancestry, from at least the earliest Neolithic. Some enclosed sites of the Neolithic and earlier Bronze Age in central Europe may be located on elevated ground or on promontories and may involve palisades or earthworks around their perimeter, just like Iron Age hillforts, so that the question arises whether these should not qualify as hillforts. To argue that their topographic location, or the scale or layout of enclosure, is not indicative of a primarily defensive purpose will not do, because some Iron Age hillforts seem to be compromised on these criteria. Nevertheless, by not entirely rational convention, hillforts as a regular class of field monuments are generally recognized from the Late Bronze Age, when their appearance in central and western Europe coincides with an intensification in the quantity and number of types of weaponry and defensive armour associated especially with the Urnfield culture. There are a number of hillfort sites in Britain where there is underlying evidence of Neolithic occupation, including occupation that was originally defined by enclosing works of earth or stone. There is no question of claiming continuity of occupation from Neolithic to Iron Age, but since the earlier earthworks would almost certainly still have been visible—at Maiden Castle, for instance, where the earliest Iron Age hillfort follows almost exactly the extent of the Neolithic enclosure—there is every reason to suppose that the existence of earthworks that would have been recognized as ancient, even if they were not formally venerated as places of ancestors, may have encouraged choice of these sites. An alternative interpretation would be simply to assume that the same advantages of location that commended themselves to Neolithic communities coincidentally satisfied equally the requirements of their Iron Age successors. But in that event the earlier monuments, like the Hambledon Hill long barrow or the Foel Trigarn cairns (Plate 14b), would hardly have been accorded the respect by later occupants that their condition indicates they were.