bluuebunny/crossref_metadata_2025 huggingface dataset:
Topological defects and low-dimensional nitride layers
Authors: Ruterana Pierre
Published: November 2023

A large research effort is going on with wurtzite nitride semiconductors, due to their large direct bandgap which provides a possibility for optoelectronic devices from red to the ultraviolet range [1]. The bandgaps of InxGa1_xN alloys cover a wide spectral range, from red (InN: l.89eV) to UV (GaN: 3.SeV), and that of the AlGaN goes to deep UV(AlN: 6.2eV). As expected, the most difficult part is InGaN, due mainly to the large mismatch (10%) between GaN and InN. In this case, ordering [2], phase separation [3], and growth instabilities have been reported [4]. For AlN and GaN, the misfit is smaller (ce2.5%) and one would expect more stable growth. The growth of quantum wells (QWs) appears to follow the 2D growth mode and that of high-quality quantum dots (QDs) has been achieved [5]. However, it was in this system that ordering along the c-axis was reported in AlGaN by Korakakis et al. [6], where the Ga and Al atoms separately occupy two simple hexagonal sublattices of the wurtzite system, giving rise to the lower symmetry P3ml space group. Active areas in visible GaN-based electroluminescent diodes (ELDs) and laser diodes (LDs) consist mainly of InGaN/GaN multiple quantum wells. Results have been published concerning the phase separation which was mainly supposed to give rise to the formation of layers composed of InN and GaN patches. This was first reported in polycrystalline InGaN films that had been annealed at temperatures below 700 °C [7]. More recently, it was shown that a ternary layer grown by molecular beam epitaxy (MBE) with In fraction larger than 30% contains regions of pure In, but atomic In concentrations up to 80% could be incorporated without phase separation in GaN/InGaN/GaN heterostructures [3]. This was tentatively explained by the fact that the two compounds have a large mismatch of lattice parameters (-10% ). In fact, the growth of InGaN layers may lead to the formation of the ternary alloy InxGa1_xN, InN and GaN, In, and finally in some cases to a ternary ordered alloy. Depending on the growth conditions one may obtain a combination of the various cases, along with the characteristic crystallographic defects.
Health economics and funding interventions: what health economics can contribute
Authors: Walley John , Wright John , Hubley John
Published: November 2023

Economists in general have a poor public image. They are associated with unintelligible graphs, an obsession with making savings, and a lack of concern for the suffering of the poor and the sick. But nothing could be further from the truth. Health economics, like public health, takes a population perspective, and asks the fundamental question: how can we get the best results, in terms of better health, from the resources which are available in this community? In pursuing this question, health economists use public health information about, for ex- ample, the effectiveness of a health programme, and combine it with information about resources (money, staff time, equipment, etc.) in order to advise on whether that programme should be pursued.
Introduction to the physics of ultracold neutrons
Authors: Ignatovich V K , Pontecorvo G B
Published: November 2023

Ultracold neutrons (UCN) are neutrons with such low energies (10−7 eV) that they can undergo total reflection from many materials at arbitrary angles of incidence, and so they can be stored in sealed vessels.
The production of UCN
Authors: Ignatovich V K , Pontecorvo G B
Published: November 2023

The production of UCN should more appropriately be termed the extraction of UCN since in the main they are only extracted from the total thermal flow of neutrons coming from the surface of the moderator of the reactor. However, even if there are UCN present in this flow, they cannot enter the neutron guide since the channel for the UCN is separated from the moderator by a wall that cannot be penetrated by UCN. This is done for technological reasons, in particular for creating a vacuum in the channel. For regeneration of UCN an additional moderator is placed inside the neutron guide; henceforth this moderator will be termed a converter. In this chapter, we shall deal with the slowing down of neutrons in the converter and also discuss the properties of the converter from the standpoint of UCN production. In some cases the regeneration of UCN is performed by directly slowing down the neutrons from higher energies mechanically or with the aid of external fields. These methods will be dealt with at the end of this chapter.
The foundation for the interaction potential of a neutron with matter
Authors: Ignatovich V K , Pontecorvo G B
Published: November 2023

Ultracold neutrons can undergo total reflection from most materials, i.e. most substances repel the neutrons. At first sight this seems quite improbable since each individual nucleus attracts neutrons. To dispel the seeming contradiction, it is necessary to analyse the main ideas relevant to the interaction of a neutron with matter. Naturally, we cannot go into details of nuclear structure or of the theory of strong interactions here, but, on the other hand, we will not restrict the scope of our discussion to the region of UCN since the issues considered here, for instance repulsion by a solid body, are characteristic of slow neutrons within a wide range of energies: from UCN up to thermal, and even higher.
Storage of UCN in material traps
Authors: Ignatovich V K , Pontecorvo G B
Published: November 2023

The main characteristic property of UCN is that they can be kept in a hermetically sealed vessel for a long time. The storage time τ is limited by the lifetime of the neutron itself, τ  β, and by the time τ  1 due to losses occurring in collisions of the UCN with the walls of the trap.The time τ  1 is determined by the cross-sections of absorption, σa, and inelastic scattering, σie, on the nuclei of the material of the walls and by the geometric dimensions of the trap l. The smaller the loss cross-section σ1 = σa + σie and the larger the value of l, the longer is the time τ. If τ  1 is significantly greater than τ  β, then the storage time τ is determined mainly by the lifetime of the neutron itself, τ  β ≈ 1000 s. Studies reveal, however, that in a weakly absorbing and sufficiently large trap the time τ is significantly smaller than the expected value. This means that the actual value of τ  1 is essentially smaller than the theoretical value, sometimes even by two orders of magnitude.
Reference data
Authors: Ignatovich V K , Pontecorvo G B
Published: November 2023

We present here, without any detailed comments, certain experimental and theoretical data which should be useful, in the main, to specialists active in the field of UCN.
The Compton scattering regime
Authors: Schülke Winfried
Published: November 2023

It has already been pointed out in Chapter 1, on the basis of more intuitive arguments, and will be derived in greater detail in Chapter 6, how the measurement of the double differential inelastic X-ray scattering cross-section can yield information about a fundamental ground-state quantity, namely the electron density in momentum space. We will summarize the relevant relations, stressing the prerequisites, on which these relations are applicable, and will then deduce practicable rules for extracting the desired information on momentum densities out of the experimental data.
The evolution of animal-like mobile robots
Authors: Holland Owen , McFarland David
Published: November 2023

As we have seen, early ethological models were often presented in terms of the familiar characteristics of contemporary physical systems, as in von Holst’s (1939) mechanical model, or Lorenz’s (1950) hydraulic model. As new technologies developed, models expressed in terms of these technologies appeared; for example, Heiligenberg’s (1974) model of the determinants of attack behaviour in cichlid fish used the symbolic language of analogue computing. However, perhaps the greatest influence on modelling in the last few decades has been the digital computer. This provided both a general model of information processing, and a range of techniques for describing and analysing information-processing systems. The scientific community soon became familiar with these ideas, and the computer became the analogy of choice: concepts such as software, hardware, flow diagrams, programs, data, processing, and memory storage became pervasive. Models could then be presented in quite abstract terms, with a computer simulation serving as an adequate investigative, illustrative, and explanatory tool.
Almost Complex Structures
Authors: McDuff Dusa , Salamon Dietmar
Published: November 2023

Every symplectic manifold admits a family of compatible almost complex structures, but none of these need be integrable. When one is, the manifold is said to be Kahler, In this chapter we discuss basic results about almost complex structures and Kähler manifolds. We may think of these as global analogues of the results in Chapter 2 which relate symplectic to complex vector bundles.
Symplectic Group Actions
Authors: McDuff Dusa , Salamon Dietmar
Published: November 2023

In this chapter we discuss symplectic manifolds with group action. There is a very basic process called symplectic reduction which is a formalization of the well known classical fact that if there is a symmetry group of dimension d acting on a system then the number of degrees of freedom of the system may be reduced by d. This means that the dimension of the phase space is reduced by 2d as both the position and the momentum coordinates are reduced by d.
Symplectic Fibrations
Authors: McDuff Dusa , Salamon Dietmar
Published: November 2023

This chapter begins with a general discussion of symplectic fibrations. Its main feature is a simple construction of a symplectic form on the total space of a symplectic fibration that is due to Thurston, The next section describes in detail the basic example of symplectic ruled surfaces. These are symplectic 2-sphere bundles over Riemann surfaces. Section 6.3 develops the notions of symplectic connection and holonomy, which were already implicit in Thurston’s proof.
Area-Preserving Diffeomorphisms
Authors: McDuff Dusa , Salamon Dietmar
Published: November 2023

An essential feature of sympleetic geometry is that there is a rich group of diffeomorphisms that preserve the sympleetic structure. This part of the book develops the basic theory of such symplectomorphisms. We begin with the 2-dimensional case in which symplectomorphisms are just areaand orientation-preserving diffeomorphisms. These arise as Poincare sections for Hamiltonian systems in a 4-dimensional phase space (in classical terminology with 2 degrees of freedom). A celebrated landmark in this subject is Poincare’s last geometric theorem, proved by Birkhoff in the 1920s, which asserts that an area-preserving twist map of the annulus must have at least two distinct fixed points. This result can be viewed as the first theorem in global symplectic geometry. We shall prove below the existence of one fixed point.
The Group of Symplbctomorphisms
Authors: McDuff Dusa , Salamon Dietmar
Published: November 2023

In this chapter we discuss the basic properties of the group Symp(M) of symplectomorphisms of a compact symplectic manifold and its subgroup Ham(M) consisting of Hamiltonian symplectomorphisms. We begin by showing that Ham(M) is a normal subgroup of Symp(Af). We then discuss the flux homomorphism (sometimes also known as the first Calabi homomorphism). The main result here is Theorem 10.12 which characterizes the Hamiltonian symplectomorphisms in terms of the flux homomorphism.
New Directions
Authors: McDuff Dusa , Salamon Dietmar
Published: November 2023

This chapter gives an outlook on the basic existence and uniqueness problems for symplectic structures. In the last few years some deep and fundamental techniques have been developed for tackling such questions. They include Taubes’ results about the Seiberg–Witten invariants and Donaldson’s construction of symplectic submanifolds and topological Lefschetz fibrations. Together with the Gromov–Witten invariants and Floer homology, they form the geometric and analytical basis for many of the new results in this area.
Resume of physical principles
Authors: Riviere J C
Published: November 2023

The surface is irradiated with an electron beam of sufficient energy, 1 to 30 keV, to ionize one or more shallow core levels in surface atoms. Following ionization the atom relaxes either by the ejection of a characteristic X-ray photon (fluorescence) or by the ejection of an Auger electron, but for shallow levels the latter process is by far the more probable. The Auger process for an atom in a solid is shown schematically in Fig. 2.1.
Electron excitation: inverse photoemission spectroscopy (IPES)
Authors: Riviere J C
Published: November 2023

The technique of Inverse Photoemission Spectroscopy, or IPES, was, and still is by a few workers, called Bremsstrahlung Isochromat Spectroscopy (BIS}. Both names give a clue to the mode of operation, which in principle, and to a certain extent in practice, is quite simple. The surface is irradiated with monoenergetic electrons and the bremsstrahlung photons so created are detected at a fixed wavelength, while the energy of the primary electrons is scanned. If no angular resolution is required in the measurements, then it is adequate to provide primary electrons simply from a hot filament in front of the surface being studied. However, much additional information can be obtained from angularly resolved studies, which require a focused beam, and in any case most workers already have available on their equipment one or other of the various designs of electron gun described under Section 3.2.1.
Electron excitation: electron stimulated desorption (ESD) and electron stimulated desorption ion angular distribution (ESDIAD)
Authors: Riviere J C
Published: November 2023

Electron Stimulated Desorption (ESD) and Photon Stimulated Desorption (PSD, q.v.) are probably the most notable examples of the maxim that one man’s artefact is another man’s technique. Whenever electron, or to a lesser extent, photon, probes are used for surface analysis there is always the worry that the probe itself may be changing the surface composition and/or chemistry during the measurement. In AES the number of recorded examples of electron beam effects is by now considerable. The desorption techniques, however, actually use the probe/surface interaction that is so troublesome elsewhere as a means of characterization in its own right.
Photon excitation: X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES)
Authors: Riviere J C
Published: November 2023

In conventional XPS, X-radiation from either an Al or an Mg unmonochromatized source of a type similar to that described under section 3.2.2 and illustrated in Fig. 3.7 falls on the surface of the sample to be analysed, in a chamber at ultra-high vacuum. Less frequently, and usually for special purposes, monochromatic radiation from an Al source produced according to the principle of Fig. 3.9 is used. The energies of photoelectrons ejected from the sample are measured in a Concentric Hemispherical Analyser (CHA), whose principles of operation are described under section 3.3.4, and which is shown schematically in Fig. 3.22. In most modern spectrometers the CHA has an input lens system that allows a greater solid angle of photoelectrons to be collected and in which pre-retardation of electrons to the entrance slit of the CHA is performed. A schematic diagram of a typical configuration in a spectrometer is shown in Fig. 10.1 (courtesy of Leybold Ltd.). In that case the sample for analysis is placed in a slot cut in a shaft that slides in and out of the analysis chamber, which is just one of the many different methods of rapid sample insertion that are now available on current equipment.
Photon excitation: reflection-absorption infra red spectroscopy (RAIRS) and surface enhanced Raman spectroscopy (SERS)
Authors: Riviere J C
Published: November 2023

This technique is known also as Infra-Red Reflection Absorption Spectroscopy (IRAS), by a rearrangement of title words, but RAIRS seems now to be more generally accepted. As will be described below, the modern version of infra-red spectroscopy employing Fourier transform techniques has also been applied here, leading to the acronym variations FT-RAIRS and FT-IRAS.
Thermal excitation: thermal desorption spectroscopy (TDS)
Authors: Riviere J C
Published: November 2023

TDS has been used very extensively, but not as a general analytical tool in the same sense as have XPS or AES. In basic experiments concerned with the study of the reactions between pure gases and clean solid surfaces, TDS is now regarded as an indispensable adjunct to the other techniques used principally in fundamental surface science, such as UPS, LEED, and work function measurement. Thus TDS is to be found in use in virtually every academic laboratory carrying out research into the reactivity of surfaces, but not at all in analytical laboratories associated with technological or trouble-shooting activities. Note that TDS is also known as Temperature Programmed Desorption (TPD) and Temperature Programmed Mass Spectrometry (TPMS).
How to fill space with atoms in condensed matter states
Authors: Janot C
Published: November 2023

We are most familiar with condensed matter in the form of solid crystalline substances, and the physics of condensed matter is to a very great extent the physics of crystals. Crystals exhibit perfect translational symmetry which introduces interesting selection rules which can be applied usefully in the interpretation of experiments as well as in theoretical modelling.
Real quasicrystals: preparation and characterization
Authors: Janot C
Published: November 2023

Even if Chapter 1 has been convincing enough for the reader to be persuaded that quasiperiodic arrangements of atoms are a possible state of matter, this by no means implies that real materials do fulfil such a type of order. This is the purpose of Chapter 2: to prove this point by describing how quasi crystals can be prepared.
Phonons, phasons, and dislocations in quasicrystals
Authors: Janot C
Published: November 2023

In studying quasi crystal structures in the last two chapters, it has mostly been assumed that atoms were at rest at their lattice sites and that there was no moving or static defect within the atomic arrangements. Atoms, however, as in normal crystals, are not quite stationary but oscillate around their equilibrium positions as a result of thermal energy, and experience occasional jumps from site to site. These dynamics and defect aspects have a fundamental influence on the thermal, acoustic, optical, and mechanical properties of the materials.
Universality
Authors: Binney J J , Dowrick N J , Fisher A J , Newman M E J
Published: November 2023

In Chapters 10 to 12 we have seen that the critical exponents of the Landau-Ginzburg model agree well with experiment (see Box 14.1 for a summary of results). This is good, but it is also slightly surprising. The Landau-Ginzburg Hamiltonian is one of the simplest possible non-Gaussian Hamiltonians, containing only one non-Gaussian term. Even the Ising model has an effective Hamiltonian which is much more complicated than this (see Appendix K). Yet not only do the critical exponents of the Landau-Ginzburg model agree with those of the Ising model, they agree with those of real physical systems too. This requires an explanation.
Experimental Techniques in Low-Temperature Physics
Authors: White Guy K , Meeson Philip J
Published: November 2023

Like for its three predecessors, the purpose of this fourth edition is chiefly to help physicists, physical chemists, materials scientists, metallurgists, engineers, and biologists to carry out investigations at low temperatures. This new edition takes into account the major changes in cryogenic technology over the past twenty years. These changes include areas of temperature measurement and control, superconducting magnets, cryocoolers, ultra-low temperatures, technical data on materials, commercially available cryostats for optical, x-ray, thermal and electrical measurements. Less emphasis is now placed on methods of constructing cryostats in the laboratory and more emphasis on commercially available cryostats, temperature controllers, and closed circuit cryocoolers. The book contains comprehensive, up-to-date tables of physical property data on metals, polymers, and ceramics. It will be of value to graduate students as well as to engineers and biologists facing cryogenic problems.
Cryostats for 1-300 K
Authors: White Guy K , Meeson Philip J
Published: November 2023

There are now many cryostats available ‘off the shelf’ which cover a wide temperature range; for example, flow cryostats suited to optical or X-ray studies, closed-cycle systems (cryocoolers) with experimental chambers or cold fingers attached and multi-property liquid-cooled cryostats (e.g. from Quantum Design and Oxford Scientific). Even if these cryostats are adequate for measuring heat capacity or thermal conductivity or optical absorption, it is useful to understand the different requirements and limitations that are imposed by different property measurements.
Magnets
Authors: White Guy K , Meeson Philip J
Published: November 2023

Magnets are a ubiquitous part of experimental low-temperature work. Their uses range from small magnets, say below I T, used to operate superconducting heat switches or for NMR thermometry to intense high-field magnets, achieving in excess of 50 T, commonly used to apply quantizing fields for experiments on electrons in metals and semiconductors. The widespread usefulness of magnets in low-temperature physics stems ultimately from two reasons: (i) the metallurgical advances in superconducting wire since the 1960s and the consequent ready commercial availability of wire in all sorts of high-grade formats; and (ii) the similarity in energy between the Zeeman splitting achievable with modern magnets and the temperatures now easily available.
Statistical Mechanics
Authors: Krauth Werner
Published: November 2023

This book discusses the computational approach in modern statistical physics in a clear and accessible way and demonstrates its close relation to other approaches in theoretical physics. Individual chapters focus on subjects as diverse as the hard sphere liquid, classical spin models, single quantum particles and Bose-Einstein condensation. Contained within the chapters are in-depth discussions of algorithms, ranging from basic enumeration methods to modern Monte Carlo techniques. The emphasis is on orientation, with discussion of implementation details kept to a minimum. Illustrations, tables and concise printed algorithms convey key information, making the material very accessible. The book is completely self-contained and graphs and tables can readily be reproduced, requiring minimal computer code. Most sections begin at an elementary level and lead on to the rich and difficult problems of contemporary computational and statistical physics. The book will be of interest to a wide range of students, teachers and researchers in physics and the neighbouring sciences. An accompanying CD allows incorporation of the book’s content (illustrations, tables, schematic programs) into the reader’s own presentations.
Dynamic Monte Carlo methods
Authors: Krauth Werner
Published: November 2023

In the first six chapters of this book, we have concentrated on equilibrium statistical mechanics and related computational-physics approaches, notably the equilibrium Monte Carlo method. These and other approaches allowed us to determine partition functions, energies, superfluid densities, etc. Physical time played a minor role, as the observables were generally time-independent. Likewise, Monte Carlo “time” was treated as of secondary interest, if not a nuisance: we strove only to make things hap pen as quickly as possible, that is, to have algorithms converge rapidly. The moment has come to reach beyond equilibrium statistical mechanics, and to explore time-dependent phenomena such as the crystallization of hard spheres after a sudden increase in pressure or the magnetic re sponse of rising spins to an external field switched on at some initial time.
The evolution of virulence in AIDS viruses
Authors: Holmes Edward C
Published: November 2023

Acquired Immune Deficiency Syndrome (AIDS) was first described in 1981 when clusters of gay men living in a number of American cities were found to be suffering from a variety of rare opportunistic infections caused by a deficiency in CD4+ T-helper cells, a crucial part of the human immune system. Within two years the cause of AIDS, a retrovirus later christened the human immunodeficiency virus type-1 (HIV-1) was isolated, with a related virus, HIV-2, discovered a few years later. Since this time HIV has spread worldwide causing a global pandemic.
The timing of sex in cyclically parthenogenetic rotifers
Authors: Serra Manuel , Snell Terry W , King Charles E
Published: November 2023

Cyclical parthenogenesis is a mode of reproduction that combines parthenogenesis with episodic sexual recombination. It has evolved independently several times, but is largely restricted to parasitic trematodes, gall wasps, gall midges, aphids, and two groups of zooplankters: cladocerans and monogonont rotifers (Bell 1982; see also De Meester et al., Chapter 11). Cyclical parthenogenesis can be regarded as an optimal combination of a demographic phase during which there is rapid clonal propagation, and a sexual phase during which meiosis and recombination create new genotypic variation. Each of these phases has its own evolutionary and ecological advantages and costs.
Introgression and hybrid speciation via transposition
Authors: Fontdevila Antonio
Published: November 2023

Since the advent of the biological species concept (Dobzhansky 1937), defined as a set of interbreeding populations reproductively isolated from other similar sets, interspecific hybrids have been stigmatized as low fitness genotypes due to the supposedly highly effective reproductive isolation mechanisms inherent to true species. Consequently, hybrids were viewed as lineages devoid of evolutionary significance. Ironically, some early naturalists, including Linnaeus and later several neo-Darwinian evolutionists such as Anderson, Stebbins, and Grant, considered hybridization as a source of new species (Arnold 1997).
Molecular evidence on the origin of and the phylogenetic relationships among the major groups of vertebrates
Authors: Zardoya Rafael , Meyer Axel
Published: November 2023

Vertebrates are a good model to study macroevolutionary patterns and processes because they possess a comparatively well known fossil record (Carroll 1997). Thanks to the detailed investigations of several generations of morphologists and paleontologists over the last two centuries, it has been possible to reconstruct the phylogeny of vertebrates with some degree of confidence (Fig. 18.1). A robust phylogenetic framework of vertebrates is fundamental for comparative studies in this group.
Soviet Pilgrims
Authors: Brown Andrew
Published: November 2023

Sage and Eileen were a politically active couple during their London years, but when they returned to Cambridge in the autumn of 1927, Eileen could not easily resume her Labour Party work and Sage’s first priority was to organize his new department. Although most of his political comrades from undergraduate days such as Dickinson, Hutt and Montagu had moved to start careers in other places, Maurice Dobb was an economics don at Trinity College and poised to become the most influential communist in the University. While Sage may have let his CPGB membership lapse, his affiliation was never in doubt or concealed. One can speculate that having renounced the Catholic Church, which once offered him such comfort, Bernal was eager for any alternative system of beliefs that would bring a comparable level of certainty to his life. In Microcosm, Bernal recognized the integrative nature of his own mind, and it is not surprising that all-encompassing philosophies like Freudianism and Marxism appealed to him. The combination of the two isms, each with its closed ideology irrefutable by discordant facts and each undermining the bourgeoisie, was fashionable in intellectual circles of the day.
Bombing Strategy
Authors: Brown Andrew
Published: November 2023

Although the crucial Battle of Britain was won by the magnificent few of Fighter Command, the RAF from its inception had been intended as an offensive bomber force. Sir Hugh Trenchard, the first Chief of Air Staff, pointed out to his fellow chiefs in 1929 that an air force held an advantage over an army or navy in being able to take the fight directly to the enemy nation, without needing to defeat its armed forces first. It could therefore ‘attack direct the centres of production, transportation and communication from which the enemy war effort is maintained’. Even more than the physical damage that an air force could wreak, Trenchard was aware of the fear that would be induced by heavy bombing and estimated that ‘the moral effect of bombing stands undoubtedly to the material effect in a proportion of twenty to one’.
Central Dogma
Authors: Brown Andrew
Published: November 2023

In the 1930s, the Rockefeller Foundation supported several small European meetings where physicists were invited to pollinate the debate about fundamental problems in biology. One of these gatherings took place at Klampenborg, about ten kilometres from Copenhagen, early in April 1938. A mixed British contingent of scientists, with Astbury and Bernal representing X-ray crystallography, attended. The crossing from Harwich to the Hook of Holland was distinctly rough, and while most of the party attempted to sleep despite the rolling of the ship, Bernal sat up in the second-class lounge deep in conversation with a tall, rather sleek, young man. His companion was Cyril Darlington, Director of the John Innes Horticultural Institute – a geneticist who had recently written on the coiling of chromosomes. Darlington had proposed that this observable alteration in chromosomal form might be due to an invisible molecular spiral in the constituent nucleoprotein. During the night, Darlington taught Sage ‘all the genetics and cytology anyone needs to know’.
Years Of Struggle
Authors: Brown Andrew
Published: November 2023

Bernal and Margot Heinemann were well matched: both shared a passion for literature and politics. The 1950s was probably Bernal’s most stable decade domestically, although he was far from settled into a conventional style of life. Soon after Jane was born, they moved to a house in Highgate (a move probably financed from the Stalin Peace Prize). The house was not lavish and the family’s material needs were met by Sage’s professorial salary of over £2,000 per annum. In the 1950s, it was quite shocking for an unmarried couple to be living together and raising a child, let alone when the man was still married to another woman. There were also the added complexities that attached to being a communist household – although such a distinction mattered less in London than it did in communist states.
Elliptic Problems
Authors: Tayler A B
Published: November 2023

In Chapter 2 a linear partial differential equation in two independent variables was defined to be hyperbolic if there exist two real distinct characteristic directions at each point, which define curves across which discontinuities in the first derivatives of the unknown function can occur.
The design and analysis of biodiversity experiments
Authors: Schmid B , Hector A , Huston M A , lnchausti P , Nijs I , Leadley P W , Tilman D
Published: November 2023

Biodiversity changes have been recognized as one of the major components of global change (Chapin et al. 2000). The investigation of the potential consequences that changes in biodiversity can have on ecosystem processes has aroused considerable interest (Naeem et al. 1994a; Tilman et al. 1996; Leadley and Korner 1996; Hooper and Vitousek 1997; Hector et al. 1999; Wardle et al. 1999; Van der Putten et al. 2000) as well as debate on the ecological interpretations and the scale of the inference that can be drawn from recent experiments (Grime 1997; Huston 1997; Wardle 1999; Huston et al. 2000). Despite these challenges, we believe that the experimental approach can help us to understand the links between biodiversity, community- and ecosystem-level processes, and abiotic factors better (Bazzaz 1996; Lawton 2000; Loreau et al. 2001).
Core Polarization
Authors: Castel B , Towner I S
Published: November 2023

It has already been pointed out that the measured magnetic moments for odd-mass nuclei differ significantly from the extreme single-particle estimates. In terms of the Schmidt diagrams, Figs. 1.1 and 1.2, experimental magnetic moments lie for the most part between the Schmidt lines. In this chapter we begin our discussion of why this is so. There are two principal reasons. One, the extreme single-particle model is too simplistic; there will be configuration admixtures which can be small in magnitude but which nonetheless can have a significant impact on the calculated magnetic moments. These corrections represent an inadequacy of the wave function and are the subject of the present chapter. Second, the form of the magnetic moment operator may be incomplete. There are corrections to the operator arising from the fact that nucleons in the nucleus are interacting with each other through the exchange of mesons. These processes lead to additional terms to the magnetic moment operator that are of two-body character. These meson-exchange current (MEC) processes will be discussed in the next chapter.
Nuclear Moments: Future Directions
Authors: Castel B , Towner I S
Published: November 2023

In recent years, progress in knowledge of nuclear moments has developed along several branches beyond the magnetic dipole and electric quadrupole moments which have been the focus of our attention so far. We devote this chapter to a discussion of what we consider are promising new directions in investigations involving nuclear moments. We first discuss E4 moments and transitions before turning to monopole transitions and concluding with an appraisal of a current relativistic model.
Introduction
Authors: Yeomans J M
Published: November 2023

A phase trans1t10n occurs when there is a singularity in the free energy or one of its derivatives. What is often visible is a sharp change in the properties of a substance. The transitions from liquid to gas, from a normal conductor to a superconductor, or from paramagnet to ferromagnet are common examples. The phase diagram of a typical fluid is shown in Fig. 1.1. As the temperature and pressure are varied water can exist as a solid, a liquid, or a gas. \Yell-defined phase boundaries separate the regions in which each state is stable. Crossing the phase boundaries there is a jump in the density and a latent heat, signatures of a first-order transition.
Models
Authors: Yeomans J M
Published: November 2023

The aim of this chapter is to describe some of the most fundamental models of cooperative behaviour. To model a physical system one route is to include, as realistically as possible, all the complicated many body interactions and try to obtain a quantitative prediction of the behaviour by solving Schrödinger’s equation numerically. The other extreme is to write down the simplest possible model that still includes the essential physics and hope that it is tractable to analytic or precise numerical solution. The aim here is often to study universal behaviour or to gain a qualitative understanding of the physics governing the behaviour of a given class of materials.
The transfer matrix
Authors: Yeomans J M
Published: November 2023

The aim of this chapter is to describe how transfer matrices can be used to solve one-dimensional classical spin models. The idea is to write down the partition function in terms of a matrix, the transfer matrix. The thermodynamic properties of the model are then wholly described by the eigenspectrum of the matrix. In particular the free energy per spin in the thermodynamic limit depends only on the largest eigenvalue and the correlation length only on the two largest eigenvalues through simple formulae.
Series expansions
Authors: Yeomans J M
Published: November 2023

Exact power series expansions for thermodynamic functions have in the past proved an invaluable aid to understanding the critical behaviour of insoluble models. Indeed, the first suggestions of power law singularities at criticality were based on such analyses. Immediately before the renormalization group was proposed, work using series expansions had led to a large body of evidence that exponents had universal properties, that they were the same above and below the critical temperature, and that mean-field values set in abruptly above four dimensions.
The renormalization group
Authors: Yeomans J M
Published: November 2023

The approaches described so far in this book have given a broad phenomenological understanding of critical phenomena. However, although a substantial framework of results and connections has been built up, we have, as yet, no explanations for the following: What is needed is a theory, based on the physics of what is happening at the critical point. we argued in Chapter 1 that the special feature of criticality is that the correlation length is infinite and that the critical system is invariant on all length scales. The aim is to write down a (hopefully short, elegant, and comprehensible) mathematical theory which embodies this physics and explains all the observations listed above. A useful theory will also allow the calculation of critical exponents and transition temperatures, if not exactly, then within an accurate and well-controlled approximation scheme.
Catechol O-methyltransferase (COMT) and COMT Inhibitors
Authors: Männistö P T , Ulmanen I , Taskinen J , Kaakkola S
Published: November 2023

Catechol O-methyltransferase (COMT, EC 2.1.1.6) is a ubiquitous enzyme in nature, occurring in various plants, microorganisms (e.g. bacteria and yeasts), invertebrates, and vertebrates, including elasmobranchs (e.g. sharks), amphibians (e.g. frogs), birds, and mammals (Guldberg and Marsden 1975; Sariaslani and Rosazza 1983). It is unlikely that all of them share the same COMT protein(s). COMT is distributed throughout the various organs. In mammals, the highest sactivities are in liver and kidney.
Inhibitors of Aldose Reductase
Authors: Dvornik Dushan
Published: November 2023

Aldose reductase (AR) inhibitors are designed to interfere with the initiation and early development of secondary complications of chronic diabetes mellitus. The concept was deduced from the insight that, in diabetic tissues with insulin-independent glucose uptake, excess glucose is metabolized via the polyol (sorbitol) pathway. The polyol pathway comprises two enzymatic reactions: in tandem, glucose is reduced to sorbitol by AR using NADPH, and sorbitol is oxidized to fructose by sorbitol dehydrogenase using NAD+ (Fig. 16.1). According to Vander Jagt et al. (1990), AR functions as an NADPH-binding protein, thus facilitating oxidation of NADPH. In contrast with other aldehyde or ketone reductases, such as lactate dehydrogenase (LDH) or alcohol dehydrogenase (ADH), AR is almost exclusively a ‘one-way catalyst, with a ratio of catalytic efficiency for the forward versus the reverse reaction that is 1000-100 000 times higher than that for either LDH or ADH (Grimshaw 1991).
Miscellaneous Topics
Authors: Schwartz J C , Gros C , Duhamel P , Duhamel L , Lecomte J M , Bralet J
Published: November 2023

Two major hormonal peptide systems appear to play opposite roles in the regulation of electrolyte balance and blood pressure, so that their imbalance might be responsible for cardiovascular and salt-retention dis orders affecting much of the population. The first is the renin-angiotensin-aldosterone system which several classes of established or potential antihypertensive agents, namely the inhibitors of angiotensin-converting enzyme (ACE; EC 3.4.15.1), tend to oppose. The second consists of atrial natriuretic factor (ANF), also called atrial natriuretiic peptide (ANP), a 28 amino acid peptide (Fig. 17A.1) secreted by the heart into the circulation to decrease blood pressure, raise the urinary excretion of water and sodium, and lower plasma renin and aldosterone levels (Brenner et al. I 990).
Introductory survey
Authors: Lovesey S W , Collins S P
Published: November 2023

Our purpose in this chapter is to give an introductory survey of the physical properties of magnetic materials that have recently been investigated by X-ray techniques. Hence, we cover the nature of the relevant techniques, namely absorption (dichroism) and elastic (diffraction) and inelastic (spectroscopy) scattering, and representative examples of materials that have been investigated. Later chapters expand on all aspects of the material, ranging from experimental methods, properties of synchrotron photon sources, and instrumentation through to a theoretical framework for the interpretation of measured signals at an atomic level of detail. For the moment, though, it is our goal to provide an overview of our subject, with minimal attention to finer points.
Non-resonant magnetic diffraction from antiferromagnets
Authors: Lovesey S W , Collins S P
Published: November 2023

The availability of experimental data on magnetic X-ray scattering has prompted a number of authors to develop cross-sections which include magnetic interactions; for diffraction a seminal paper is de Bergevin and Brunel (1981). However, despite a surge of activity over recent years, with a strong emphasis on elastic magnetic diffraction, the influence of electronic spin on photon scattering amplitudes has in fact been understood for a long time. A number of papers on the scattering cross-sections for an isolated polarized electron have appeared since the famous work of Klein and Nishina (1929), who derived an exact expression for the scattering of an electromagnetic wave from a free electron. One of the most interesting of these papers is that of Gell-Mann and Goldberger (1954), who developed the magnetic scattering amplitude using both classical physics and quantum mechanics. The important result was to demonstrate that for photon energies which are very low in comparison with the electron energy, the quantum and classical formalisms give exactly the same result. Although the electronic spin itself does not appear naturally from classical physics and has to be added in a rather ad hoc manner, the result is none the less useful as an aid to visualizing the physics behind magnetic scattering.
Non-resonant magnetic diffraction from ferromagnets
Authors: Lovesey S W , Collins S P
Published: November 2023

In the previous two chapters we learnt that magnetic (Bragg) diffraction intensities, generated by the magnetic cross-section ((1.4) and (2.34), for example), are generally very much weaker than those of charge scattering, often by 6-8 orders of magnitude.
Kinematics and dynamics of electrons and holes in energy bands
Authors: Balkanski M , Wallis R F
Published: November 2023

One of the features that distinguishes semiconductors from metals is that the current carriers can include not only electrons in the conduction band, but also empty electron states or holes in the valence band. The dynamical response of these current carriers to external electric and magnetic fields is strongly affected by the energy band structure of the semiconductor and is characterized by their effective mass and charge. These parameters can be determined by means of cyclotron resonance and Hall effect, respectively.
Surface properties of semiconductors
Authors: Balkanski M , Wallis R F
Published: November 2023

The physical boundaries of a semiconductor are found to produce significant effects on its electronic and vibrational properties. If the boundary separates the semiconductor from vacuum or a gas, it is referred to as a surface. If the semiconductor is separated from a liquid or a solid, the boundary is called an interface. Many of the technological applications of semiconductors are based on surface and interface effects. In the present chapter we focus on surface effects and defer our consideration of interface effects to Chapter 15.
Semiconductor lasers and photodevices
Authors: Balkanski M , Wallis R F
Published: November 2023

The term laser is an acronym for Light Amplification by the Stimulated Emis sion of Radiation. The concept of stimulated emission is due to Einstein, whose studies of the statistical mechanics of electromagnetic radiation indicated that the usual treatment based on induced absorption and spontaneous emission violates the principle of detailed balance. In order to correct this deficiency, Einstein introduced the notion that a system in an excited state is stimulated by the radiation field to emit a photon and drop to a lower energy state.
The motion of bodies along conic sections
Authors: Chandrasekhar S
Published: November 2023

The propositions of Section III and most particularly Proposition XI (in which the inverse-square law of attraction is deduced for bodies revolving in ellipses under the action of a ‘a centripetal force tending to the focus of the ellipse’) are commonly regarded as the apex of the Principia. This view, in my judgement, greatly diminishes the Principia. Newton himself did not accord Proposition XI any special significance when he came to formulating his universal law of gravitation in Book III: his main references are to Propositions I-IV and especially Proposition IV and its seven ccrollaries (see Chapter 19).
Kepler’s equation and its solution
Authors: Chandrasekhar S
Published: November 2023

presentation of Section III of the Principia was completed in Chapter 6. Sections IV and V which follow are of the nature of an intermezzo: in them we are led into the realm of the conic sections that forms the background against which the rest of the play is to be enacted. There is much of interest in these sections. But we shall pass them by since they are not essential to the subsequent developments; and besides there is an excellent account of them by J. J. Milne that is already available (Isaac Newton,1642-1727, a memorial volume, W. J. Greenstreet, London 1927, pp. 96-114).
On revolving orbits
Authors: Chandrasekhar S
Published: November 2023

Newton introduces the subject of this Section IX at the conclusion of Section VIII thus: I have hitherto considered the motions of bodies in immovable orbits. It remains now to add something concerning their motions in orbits which revolve round the centres of force. The problem he considers is the following. We know that under a centripetal law of attractive force a body is constrained to move in a fixed plane; and that it describes in this plane equal areas in equal times. Let r = f(</J) be such an orbit described under a centripetal force P(r). Consider the locus r = f(rx</J) where rx is some prescribed constant.
The universal law of gravitation
Authors: Chandrasekhar S
Published: November 2023

After his Prolegomenon (Chapter 18), Newton proceeds to the deduction of his universal law of gravitation in the first 14 Propositions of Book III. We shall begin by listing the 19 propositions of Book I, the three propositions of Book II, and the Rules of Reasoning that will serve as the basis of Newton’s reasoning. An examination of this list is already of interest for revealing the priorities that Newton attaches to the various propositions; and in particular to Proposition XI (and XLI) in which he proved that a body will revolve in an elliptic orbit about its focus if acted upon by a centripetal force inversely as the square of the distance from the focus. It will be recalled that it was on hearing from Newton (in August, 1684) that he had proved this proposition ‘some years earlier’ and on receiving in the same year (November, 1684) De M otu Corporum in Gyrum in which the proposition is proved, that Halley persuaded Newton to embark on what was to become Philosophie naturalis Principia Mathematica. Nevertheless, Newton refers to Proposition XI only casually —almost as an afterthought¬ in the last but one of the 14 propositions that comprise this section. Newton’s priorities are clearly different.