Showing papers in "Reports on Progress in Physics in 1980"
TL;DR: The theory of two-dimensional turbulence is reviewed and unified, and some hydrodynamic and plasma applications are considered in this paper, where some equations of incompressible hydrodynamics, absolute statistical equilibrium, spectral transport of energy and enstrophy, turbulence on the surface of a rotating sphere, turbulent diffusion, MHD turbulence, and two dimensional superflow are discussed.
Abstract: The theory of two-dimensional turbulence is reviewed and unified, and some hydrodynamic and plasma applications are considered. The topics covered include some equations of incompressible hydrodynamics, absolute statistical equilibrium, spectral transport of energy and enstrophy, turbulence on the surface of a rotating sphere, turbulent diffusion, MHD turbulence, and two-dimensional superflow. Finally, an attempt is made to assess the status and future of the principal research topics which have been discussed.
1,056Â citations
888Â citations
712Â citations
TL;DR: In this article, a critical review of idealized two-phase geometrical models is given, which derive expressions for the resistivity and Hall coefficient of a composite material in terms of the properties of its constituents.
Abstract: Gives a critical review of idealised two-phase geometrical models. These treatments derive expressions for the resistivity and Hall coefficient of a composite material in terms of the properties of its constituents. The authors show that these models can be applied to the interpretation of transport measurements in polycrystalline films and powder layers. Important distinctions are made depending on whether the depletion layers extend completely or partially through the grains, whether the Debye length is greater or less than the grain size and whether the mean free path is greater or less than the grain size. The authors discuss the theoretical treatment of the Hall effect in percolative systems, as geometrical models neglect percolation. The modulation of Hall coefficient and conductivity by illumination and the adsorption and desorption of ambient gases are also considered.
539Â citations
CERN1
TL;DR: In this article, the authors lay a theoretical basis for both the traditional Monte Carlo and quasi-Monte Carlo methods, and present some practical aspects of when and how to use them.
Abstract: The Monte Carlo method has long been recognised as a powerful technique for performing certain calculations, generally those too complicated for a more classical approach. Since the use of high-speed computers became widespread in the 1950s, a great deal of theoretical investigation has been undertaken and practical experience has been gained in the Monte Carlo approach. The author tries to lay a theoretical basis for both the 'traditional' Monte Carlo and quasi-Monte Carlo methods, and, to present some practical aspects of when and how to use them. An important theme is the comparison of Monte Carlo, quasi-Monte Carlo and numerical quadrature for the integration of functions, especially in many dimensions.
432Â citations
TL;DR: In this article, the authors review the mainstream developments in quantum chemistry and give a straightforward account of some of the many-body techniques borrowed, with appropriate modifications, from other areas of physics-field theory, nuclear theory and solid-state theory.
Abstract: With the increasing availability of powerful computers, attempts to calculate the electronic structure and properties of molecules by the direct ab initio solution of a many-body Schrodinger equation have received a great stimulus. The authors review the mainstream developments in quantum chemistry and give a straightforward account of some of the many-body techniques borrowed, with appropriate modifications, from other areas of physics-field theory, nuclear theory and solid-state theory. After a historical introduction, the traditional approach based on the self-consistent field and the method of configuration interaction is developed in detail. This is followed by the introduction of the cluster expansion, various types of correlated electron-pair theory, and diagrammatic perturbation methods. Finally, propagator and Green function techniques are reviewed, not only as a means of calculating transition energies but also as an alternative approach to the determination of the electronic ground state.
325Â citations
TL;DR: In this article, the main experimental work in the single-beam case is on resonance fluorescence; the relevant theory is reviewed in some detail, with particular emphasis on the simpler aspects of the calculations.
Abstract: Measurements on non-classical effects fall into two categories depending on whether the two intensities or photon counts to be correlated refer to a single light beam or to two different beams. The main experimental work in the single-beam case is on resonance fluorescence; the relevant theory is reviewed in some detail, with particular emphasis on the simpler aspects of the calculations. Alternative proposals for generating non-classical single beams by non-linear optical experiments are reviewed more briefly. A similar coverage of double-beam experiments is given, with a detailed account of the theory of non-classical correlations between the light beams generated in two-photon cascade emission, and a briefer survey of corresponding non-linear optical experiments.
219Â citations
TL;DR: In this article, a review of the analysis and interpretation of the satellite lines in terms of the physical parameters characterising the emitting plasma is presented, and extensive results concerning the astrophysically important hydrogen-like and helium-like ions are summarised.
Abstract: Dielectronic recombination is a process particularly effective in high-temperature dilute plasmas such as those observed, for example, in astrophysics. This process was first recognised for its noticeable effects on the establishment of ionisation equilibrium in the solar corona. Over the last decade, its importance as a line formation mechanism has been emphasised. It is responsible for spectral lines appearing as satellites to the long-wavelength side of the resonance lines of the highly ionised systems typical of hot plasmas. However, in transient ionising plasmas and for the heavier ions these lines can also be produced by direct excitation of an inner-shell electron. This review is concerned essentially with the analysis and interpretation of the satellite lines in terms of the physical parameters characterising the emitting plasma. Extensive results concerning the astrophysically important hydrogen-like and helium-like ions are summarised. These are compared with the few available high-resolution soft X-ray spectra of solar active regions and flares.
193Â citations
TL;DR: In this article, the essential structural aspects together with the characteristic superconducting properties and information on electron and phonon spectra are reviewed, along with the characteristics of A15-type compounds.
Abstract: Superconducting A15-type compounds were discovered 25 years ago. Several thousand original publications have appeared on this growing subject. The author reviews the essential structural aspects together with the characteristic superconducting properties and information on electron and phonon spectra.
131Â citations
TL;DR: The present state of understanding of the dynamics of magnetic domain walls and magnetic bubbles is reviewed in this paper, where the theory of domain wall motion for the linear and non-linear regions is outlined.
Abstract: The present state of understanding of the dynamics of magnetic domain walls and magnetic bubbles is reviewed The theory of domain wall motion for the linear and non-linear regions is outlined Experimental techniques for straight walls and magnetic bubbles are discussed An extensive comparison between theory and experiment is made Topics included are peak and saturation velocities, mobility, inertial effects and overshoot, hard bubbles, wall states and state transformations in magnetic bubbles Origins of wall damping are also discussed
115Â citations
TL;DR: In this paper, anomalies have been discovered in the isotopic composition of a number of elements which cannot be explained by processes known to be going on within the solar system at present.
Abstract: The classical picture of the pre-solar nebula is that of a hot, well-mixed cloud of chemically and isotopically uniform composition. Recent measurements have shown this conception to be erroneous, however. Anomalies have been discovered in the isotopic composition of a number of elements which cannot be explained by processes known to be going on within the solar system at present. Rather, they appear to reflect primordial heterogeneities, testifying to variations in space and/or time of the isotopic composition of these elements within the proto-solar nebula. They contribute to our understanding of processes and of time scales in the early solar system, before and after its formation. Furthermore, they allow one to identify modes of nucleosynthesis and to derive relevant parameters of such production modes.
TL;DR: In the case of collision-dominated, high-pressure arcs, the important role of radiative energy transfer, including strong self-absorption, has been established through the experimental and theoretical study of cylindrically symmetric, uncontaminated arc plasmas as mentioned in this paper.
Abstract: Progress in the physics of high-power arcs has been largely due to a blend of detailed experimental and theoretical investigations aimed at explaining the electrical behaviour of the discharge in terms of fundamental physical processes. In the case of collision-dominated, high-pressure arcs the important role of radiative energy transfer, including strong self-absorption, has been established through the experimental and theoretical study of cylindrically symmetric, uncontaminated arc plasmas. As a result, an insight has been gained into the additional complications produced in naturally occurring high-pressure arcs by electrode vapour contamination and self-magnetically-propelled plasma flows. The application of similarity theory based upon the conservation equations of fluid mechanics has produced good correlation of the properties of arcs in transverse flows and magnetic fields under a number of different operating conditions. Criteria defining stable arc operation have been derived using stability theory whilst axisymmetric instabilities of arcs in accelerating flows have been related to vortex production at the arc boundary.
TL;DR: The role of excited-state orbitals, under the influence of low-symmetry fields, is largely responsible for the different orientations of the principal directions of the various interactions experienced by a paramagnetic ion as discussed by the authors.
Abstract: Electron paramagnetic resonance (EPR) is a well-established technique for investigating the properties of metal ions in crystals, chemical complexes and biological molecules. It provides information about electronic structure and the site symmetry or nature of the environment of metal ions. The authors review the historical development of low-symmetry ideas and their theoretical basis as its major uses have been restricted to metal ions in sites of high symmetry. Major experimental results are tabulated and the discussion includes some of the attempts to interpret low-symmetry EPR data using crystal field and molecular orbital models. It is concluded that the role of excited-state orbitals, under the influence of low-symmetry fields, is largely responsible for the different orientations of the principal directions of the various interactions experienced by a paramagnetic ion.
TL;DR: In this article, a review of classical systems to which capillarity is relevant is given, with particular emphasis on pendent and sessile drops, emergent and captive bubbles, holms and fluid bridges.
Abstract: An indication is given of the wide range of classical systems to which capillarity is relevant. The basic laws are outlined with the introduction of the term effective area and Gauss's law. Interface configurations are classified, with particular emphasis on pendent and sessile drops, emergent and captive bubbles, holms and fluid bridges. These types of fluid body in a gravitational field form a major portion of the review, their properties being described from the phenomenological and thermodynamic approaches to criteria for equilibrium and stability. A distinction is made between Laplace or mechanical and Kelvin, physicochemical or diffusional equilibrium and stability. Some applications, including aspects of interfacial tension determination, are given in more detail than those used for illustration.
[...]
TL;DR: In this paper, the basic properties common to all such high-power lasers are introduced, along with detailed discussions of neodymium, CO2, and iodine laser types.
Abstract: High-power lasers are defined as systems generating pulses with powers in excess of a few gigawatts. The basic properties common to all such lasers are introduced. Specific high-power lasers are then considered with detailed discussions of neodymium, CO2 and iodine lasers.
TL;DR: In this paper, angle-resolved photoemission has been developed into one of the most powerful spectroscopic methods for studying solids, particularly when used in conjunction with light sources such as synchrotron radiation.
Abstract: Discusses photoemission from solids and their surfaces. The authors concentrate in particular on angle-resolved photoemission which has been developed into one of the most powerful spectroscopic methods for studying solids, particularly when used in conjunction with light sources such as synchrotron radiation. They discuss the basis of the technique, and briefly outline developments in experimental and theoretical methods. Then they consider examples of the application to a range of problems, to study the electronic band structure of solids, to study surface states to probe the orientation, lateral interaction and chemical state of atoms and molecules on surfaces, as well as to probe the crystallographic ordering at surfaces.
TL;DR: In this paper, the authors present a review of the techniques that are applicable to high-frequency (>or approximately =200 GHz) phonon propagation in solids, and analyse the physical principles involved, its characteristic parameters, and its range of applicability.
Abstract: It has recently become possible to observe experimentally the spectral, spatial and temporal evolution of non-equilibrium phonon distributions in solids. The author reviews those techniques which are applicable to high-frequency (>or approximately=200 GHz) phonon propagation. Each technique is analysed for the physical principles involved, its characteristic parameters, and its range of applicability. The physical phenomena, to which the techniques have been applied, are discussed and the experimentally obtained results are compared to theoretical predictions whenever possible. It is shown that, although no universally applicable phonon spectrometer has so far been devised, those spectrometers presently in use are applicable to a broad range of phenomena inherent in phonon transport.
TL;DR: In this paper, the nonlinear optical properties of condensed matter are reviewed in a phenomenological manner and the effects they describe are presented on general grounds, and the symmetry aspects of non-linear optics are discussed.
Abstract: Reviews the nonlinear optical properties of condensed matter. The non-linear optical susceptibilities are first introduced in a phenomenological manner and the effects they describe are presented on general grounds. Then the symmetry aspects of non-linear optics are discussed. The propagation of electromagnetic fields in non-linear media are considered and the device applications they result in are described. Finally, the origins of the non-linear optical behaviour of matter, either in the transparency domain or near energy level resonances are examined.
TL;DR: The high-resolution scanning transmission electron microscope has significantly different characteristics from the conventional electron microscope as discussed by the authors, it is a quantitative instrument which is capable of providing numerical data on the properties of thin specimens.
Abstract: The high-resolution scanning transmission electron microscope has significantly different characteristics from the conventional electron microscope. The process of producing images is in itself quite different but most significantly it is a quantitative instrument which is capable of providing numerical data on the properties of thin specimens. The author discusses the physics involved in the design and operation of the instrument. He has made little attempt to give details in particular designs because such details already appear in the literature. Instead emphasis is placed on the capabilities and limitations of the instrument and give some ideas of the direction of future developments.
TL;DR: In this article, the effect of parity nonconservation in nuclei is viewed as an inescapable consequence of weak interactions and the derivation of the effective weak Hamiltonian is discussed.
Abstract: Parity non-conservation in nuclei is viewed as an inescapable consequence of weak interactions. This review, starts with the derivation of the effective weak Hamiltonian, which then acts as a perturbation mixing states of the opposite parity in nuclei. The connection between the effective weak Hamiltonian and various models of weak interactions (or quantum flavour dynamics, QFD) and the strong quantum chromodynamics (QCD) is briefly reviewed. The effective weak Hamiltonian serves as an input for determining the weak parity-violating potential. This weak potential is the main tool for connecting elementary particles with nuclear physics. Its derivation is discussed extensively, with special attention to one-boson-exchange (rho meson, pion, etc) contributions. Examples of theoretical and semi-empirical weak parity-violating potentials are given. Nuclear physics aspects of parity non-conservation in nuclei are also discussed.
TL;DR: In this article, the role of neutrinos in stellar evolution, particularly in the explosion of supernovae and in the cooling of neutron stars, and the possible relationship of the net baryon number of the universe to unified models of elementary particle physics.
Abstract: The Universe provides a laboratory in which it is possible to test the laws of physics in conditions which cannot be achieved in a terrestrial laboratory. The author assumes that the laws of physics are unchanging in space and time and discusses how modern developments in elementary particle physics influence our understanding of the Universe and conversely the possibility that astronomical observations may give information about elementary particle physics. In particular he studies the physics of the early Universe and discusses the role of new particles such as heavy leptons, neutrinos and quarks and the possible relationship of the net baryon number of the Universe to unified models of elementary particle physics. He considers the role of neutrinos in stellar evolution, particularly in the explosion of supernovae and in the cooling of neutron stars. Black holes are also discussed.
TL;DR: A survey of the field of pattern recognition is presented in a manner broad enough not to be limited to the progress in recent years alone, and hence the omission of many details is unavoidable.
Abstract: A survey of the field of pattern recognition is presented in a manner broad enough not to be limited to the progress in recent years alone. In this review the emphasis is on the principal problems, methods and applications, and hence the omission of many details is unavoidable. Pattern recognition is discussed both intuitively and, more formally, as a many-to-one mapping. Several sources of variability, leading to many different possible representations of a certain pattern, are mentioned. All of these representations have to be classified as one pattern indicated by a certain class. An essential aspect of pattern recognition, relevant for this classification, is the selection of features by means of preprocessing the input data. Another essential aspect is the decision process based upon these features and leading to the classification. Several types of preprocessing are treated. Global and local transformations suitable for different types of filtering, decomposition and segmentation are indicated. A discussion of the three techniques used in pattern recognition, namely statistical, fuzzy and linguistic, is given.
TL;DR: In this paper, the experimental studies and related analyses of such processes in p-type ZnTe, GaP, SiC and InSb are surveyed and compared with the observed scattering mechanisms, including free heavy-hole spin flip, spin flip of holes bound to shallow acceptors, and several exciton processes.
Abstract: Surveys the experimental studies and related analyses of such processes in p-type ZnTe, GaP, SiC and InSb. The observed scattering mechanisms include free heavy-hole spin flip, spin flip of holes bound to shallow acceptors spin flip of photoexcited electrons, and several exciton processes. A variety of photoexcited transitions which yield spin temperatures up to 300K in systems with lattice temperatures below 2K. Multiple spontaneous spin-flip scattering and spin-flip plus phonon scattering mechanisms are discussed.