Showing papers in "Reports on Progress in Physics in 1993"
TL;DR: The transport properties of disordered solids have been the subject of much work since at least the 1950s, but with a new burst of activity during the 1980s which has survived up to the present day as mentioned in this paper.
Abstract: The transport properties of disordered solids have been the subject of much work since at least the 1950s, but with a new burst of activity during the 1980s which has survived up to the present day. There have been numerous reviews of a more or less specialized nature. The present review aims to fill the niche for a non-specialized review of this very active area of research. The basic concepts behind the theory are introduced with more detailed sections covering experimental results, one-dimensional localization, scaling theory, weak localization, magnetic field effects and fluctuations.
1,466 citations
TL;DR: In this article, the authors review the main problems presented by these complicated dynamical systems and summarize the effort so far made towards their solution, emphasizing results which appear secure, and conclude that the observed motions are consistent with material within the bar streaming along highly elongated orbits aligned with the rotating major axis.
Abstract: Some 30% of disc galaxies have a pronounced central bar features in the disc plane and many more have weaker features of a similar kind. Kinematic data indicate that the bar constitutes a major non-axisymmetric component of the mass distribution and that the bar pattern tumbles rapidly about the axis normal to the disc plane. The observed motions are consistent with material within the bar streaming along highly elongated orbits aligned with the rotating major axis. A barred galaxy may also contain a spheroidal bulge at its centre, spirals in the outer disc and, less commonly, other features such as a ring or lens. Mild asymmetries in both the light and kinematics are quite common. The authors review the main problems presented by these complicated dynamical systems and summarize the effort so far made towards their solution, emphasizing results which appear secure.
481 citations
TL;DR: A review of the development of Einstein's thought on general covariance, its relation to the foundations of general relativity and the evolution of the continuing debate over his viewpoint can be found in this paper.
Abstract: Einstein offered the principle of general covariance as the fundamental physical principle of his general theory of relativity and as responsible for extending the principle of relativity to accelerated motion. This view was disputed almost immediately with the counter-claim that the principle was no relativity principle and was physically vacuous. The disagreement persists today. This article reviews the development of Einstein's thought on general covariance, its relation to the foundations of general relativity and the evolution of the continuing debate over his viewpoint.
407 citations
TL;DR: In this paper, a review of recent developments in chiral perturbation theory (CHPT), which is the effective field theory of the standard model below the chiral symmetry breaking scale, is considered.
Abstract: In this review recent developments in chiral perturbation theory (CHPT), which is the effective field theory of the standard model below the chiral symmetry breaking scale, are considered. The effective chiral Lagrangian formulated in terms of the pseudoscalar Goldstone bosons (pi, K, eta) is briefly discussed. It is shown how one can gain insight into the ratios of the light quark masses and to what extent these statements are model independent. A few selected topics concerning the dynamics and interactions of the Goldstone bosons are considered. These are pi pi and pi K scattering, some non-leptonic kaon decays and the problem of strong pionic final-stage interactions. CHPT also allows us to make precise statements about the temperature dependence of QCD Green functions and the finite-size effects related to the propagation of the (almost) massless pseudoscalar mesons. A central topic is the inclusion of matter fields, baryon CHPT. The relativistic and the heavy-fermion formulation of coupling the baryons to the Goldstone fields are discussed. As applications, photonucleon processes, the pi N Sigma term and nonleptonic hyperon decays are presented. Implications of the spontaneously broken chiral symmetry on the nuclear forces and meson exchange currents are also described. Finally, the use of effective field theory methods in the strongly coupled Higgs sector and in the calculation of oblique electroweak corrections is touched upon.
226 citations
TL;DR: The author presents an introduction to cellular structures, discusses the fundamental role played by geometry in the evolution of these systems and surveys the recent experimental and theoretical developments in the field.
Abstract: A large class of evolving nonequilibrium systems, known collectively as cellular structures, are composed of nearly-uniform domains of polygonal-like or polyhedral-like shape (in two- or three-dimensional systems respectively) separated by thin boundaries endowed with line or surface energy. Work done mainly during the last decade has shown that the evolution of mature structures is characterized by universal or system-independent statistical distributions which possess scaling properties. The author presents an introduction to cellular structures, discusses the fundamental role played by geometry in the evolution of these systems and surveys the recent experimental and theoretical developments in the field.
192 citations
TL;DR: In this article, a review of the most recent studies in this field of research is presented, focusing on specific processes involving laterally confined (self-aligned) silicide film formation as more advanced applications require film formation only in certain localized regions on a Si wafer.
Abstract: Studies of the properties and characteristics of transition metal silicides have been stimulated by their (potential) use in integrated circuit technology. This review describes some of the most recent studies in this field of research. Formation mechanisms of silicides are discussed in some detail. A division is made between near-noble and refractory metal silicidation which aids in the understanding of differences in formation mechanisms of the various silicides. The evolution of the components of thin film stress during metal silicidation is also elucidated. In the review of the practical uses of these materials, emphasis is placed on specific processes involving laterally confined (self-aligned) silicide film formation as more advanced applications require film formation only in certain localized regions on a Si wafer.
173 citations
TL;DR: In this paper, a review of the modelling of elliptical galaxies is presented, centred on the question of their overall mass distribution and intrinsic symmetry and also taking into account the three major issues of stability, dark matter and galaxy formation.
Abstract: The article reviews the modelling of elliptical galaxies, centred on the question of their overall mass distribution and intrinsic symmetry and also taking into account the three major issues of stability, dark matter and galaxy formation. The authors illustrate how some stellar dynamical descriptions can account for the observed luminosity and velocity dispersion profiles, under plausible physical assumptions suggested by observations and N-body simulations. This modelling process currently faces nontrivial difficulties when dealing with significantly non-spherical systems; on the other hand, integrable self-consistent, stellar dynamical, triaxial models constructed so far apparently do not have a realistic density profile. The present review focuses on a few physical and methodological issues, bringing out some interesting connections between the astrophysical problem that is considered and other branches of physics. Reference is given to other review articles that complement the approach taken.
168 citations
TL;DR: In this paper, a review of elastic recoil detection (ERD) is presented, which determines the yield and energy of particles ejected out of the surface region of samples under MeV ion bombardment.
Abstract: In elastic recoil detection (ERD) one determines the yield and energy of particles ejected out of the surface region of samples under MeV ion bombardment. By application of this surface and thin film analysis technique one can obtain quantitative information concerning the depth distribution of light elements in a sample to be analysed. The quantitativity and the depth resolving power are based on knowledge of the recoil cross section and the stopping power of high-energy ions in matter. This paper reviews the fundamentals of this technique and the various experimental methods for recoil identification. Furthermore, important features for material analysis, such as detection limits, depth resolution and elemental range are discussed. Some emphasis is put on the conversion of the spectral contribution of the elements to atomic concentrations in the films for several representative cases. Throughout the review numerous examples are given to illustrate the features of ERD and to demonstrate empirically the accuracy of the quantification method.
137 citations
TL;DR: In this article, the authors summarize the progress that has been achieved in understanding surfactant monolayers, concentrating on fatty acids and phospholipids and trying to generalize the results.
Abstract: This review tries to summarize the progress that has been achieved in understanding surfactant monolayers, concentrating on fatty acids and phospholipids and trying to generalize the results. It is shown that surfactant monolayers exist in a variety of phases that are distinguished by internal and external order and a coupling or decoupling of various degrees of freedom. The interface also orients dipolar molecular moieties resulting in long range electrostatic repulsion. This causes peculiar shapes and superlattices of domains of coexisting phases. These features could be explored by introducing new experimental techniques, predominantly optical microscopies and surface X-ray scattering. These techniques are discussed together with other conventional and new ones to demonstrate which type of information could be derived. Also summarized is the status of theoretical description and simulations in relation to the experimental results.
122 citations
TL;DR: In this paper, a covariant transport model for relativistic heavy-ion collisions at energies of the order of 1 GeV is analyzed in terms of a mean field model based on nucleon and Delta-degrees of freedom and mesonic mean fields.
Abstract: Relativistic heavy-ion collisions at energies of the order of 1 GeV are analysed in terms of a covariant transport model that is based on nucleon and Delta -degrees of freedom and mesonic mean fields. The questions of possible classical meson-field radiation and of the thermal properties of the system during the collision are addressed. A detailed comparison with the experimental data obtained by the Plastic-Ball group at the BEVALAC shows that the combination of mean-field dynamics and two-body collisions is well suited for gaining an understanding of the dynamics of heavy-ion collisions. How far quantitative conclusions about the properties of nuclear matter at high densities and temperatures can be made and how future experiments can help to achieve this goal is also considered.
101 citations
TL;DR: Guided-wave devices demonstrated in lithium niobate have been seen for many years as highly functional components for applications in fields such as optical communications and sensor systems as discussed by the authors, and the subject matter of this article is born from these endeavours.
Abstract: Guided-wave devices demonstrated in lithium niobate have been seen for many years as highly functional components for applications in fields such as optical communications and sensor systems. The potential for their use has been recognized by the substantial research and development effort the technology has witnessed, and the subject matter of this article is born from these endeavours. The material reviewed includes a survey of devices built, including their design, functionality, and performance, as well as parallel activities that have been undertaken in materials processing, theory, and the development of lithium niobate itself, all of which are closely linked, and all of which have played an important part in the overall development of this major branch of contemporary optics research.
TL;DR: In this paper, a review of recent experimental effort in laser-assisted electron scattering with particular emphasis upon free-free (inverse bremsstrahlung) collisions is presented.
Abstract: New insights into our understanding of the fundamental electron-atom collision process have been made possible by combining the use of highly monochromatic electron beams and intense laser radiation. The paper reviews recent experimental effort in laser-assisted electron scattering with particular emphasis upon free-free (inverse bremsstrahlung) collisions. The excitation of an atom by simultaneous absorption of photon(s) and kinetic energy from the incident electron, the so-called SEPE process, is also discussed. The role of resonance formation in such collision cross sections is of major importance and reveals new information on the dynamics of the collision process. Modern theoretical treatments of such laser-assisted collisions are examined and shown to be only partially successful in explaining modern experimental results. The need for more rigorous theoretical calculations is clearly shown.
TL;DR: In this paper, the authors reviewed several rival theories regarding the nature of the grains and of their evolution and concluded that amorphous silicate materials and hydrogenated carbon are almost surely important constituents of grains.
Abstract: Interstellar dust has a major effect on the Universe and our view of it by strongly affecting the physical and chemical processes within the interstellar medium. Its properties are best determined by the wavelength dependence of its extinction (scattering plus absorption), reflection from nearby stars, emissions (especially in certain near-infrared bands, along with continuum), and polarization of starlight by aligned grains. There are other clues as well, such as the depletion of certain elements from the gas phase onto the grains. The extinction varies strongly with direction, typically with the outer parts of molecular clouds having less extinction in the ultraviolet (relative to the visual) than the diffuse interstellar medium. There is a rather well defined one-parameter mean extinction law extending over the whole range of wavelengths for which observations are available. There are several rival theories regarding the nature of the grains and of their evolution. Most have a common base: that amorphous silicate materials and hydrogenated carbon are almost surely important constituents of grains. Various ideas regarding the arrangements are reviewed.
TL;DR: In this article, a review of photon scattering by magnetic solids is discussed and reviewed at a fairly basic level, with an emphasis on concepts and theoretical developments for the interpretation of experimental results.
Abstract: Photon scattering by magnetic solids is discussed and reviewed at a fairly basic level, with an emphasis on concepts and theoretical developments for the interpretation of experimental results. Achievements to date are illustrated by reference to some experiments reported in the past few years, and all performed with photon beams produced by electron synchrotron facilities. The review covers photon (Bragg) diffraction, Compton scattering, elastic resonant scattering and linear and circular dichroism.
TL;DR: In this paper, the basic concepts of lattice gauge theories are described, including a discussion of currently used algorithms and the reconstruction of continuum physics from lattice data, and some results for QCD, both at low energies and at high temperatures, as well as for the electroweak sector of the standard model.
Abstract: Numerical simulations have become an important tool to understand and predict nonperturbative phenomena in particle physics. We attempt to present a general overview over the field. First, the basic concepts of lattice gauge theories are described, including a discussion of currently used algorithms and the reconstruction of continuum physics from lattice data. We then proceed to present some results for QCD, both at low energies and at high temperatures, as well as for the electro-weak sector of the standard model.
TL;DR: In this paper, the authors present a review of radio emission mechanisms, types of radio stars and their relationship to stellar evolution, mass-losing stars, enhanced activity stars, chemically peculiar stars, emission related to mass transfer, astrometric aspects.
Abstract: The author presents a review, discussing: radio emission mechanisms, types of radio stars and their relationship to stellar evolution, mass-losing stars, enhanced activity stars, chemically peculiar stars, emission related to mass transfer, astrometric aspects.
TL;DR: Reflection electron microscopy (REM) is a new technique for real space imaging of bulk crystal surfaces as discussed by the authors, which is performed in a transmission electron microscope (TEM) or a scanning TEM (STEM) using high-energy electrons at a grazing incidence angle.
Abstract: Reflection electron microscopy (REM) is a new technique for real space imaging of bulk crystal surfaces. The REM is performed in a transmission electron microscope (TEM) or a scanning TEM (STEM) using high-energy electrons at a grazing incidence angle. A comprehensive review has been given on basic techniques, fundamental physics, studies of surface reconstructions, and special applications of REM. Theoretical calculations have been described to illustrate the resonance scattering processes of electrons at the bulk crystal surfaces in the geometry of reflection high-energy electron diffraction (RHEED). Fundamental contrast mechanisms of REM have been illustrated to show the surface sensitivity of REM. Applications of REM for in-situ imaging of surface dynamic processes have been summarized for studies of metals, semiconductors, metal-on-semiconductors, semiconductor-on-semiconductors, and ceramics. Inelastic excitations of crystal surfaces in RHEED have been examined to demonstrate a technique, reflection electron energy-loss spectroscopy (REELS), for studying surface electronic structures and determining surface chemical compositions. Finally, novel techniques used in conjunction with REM, such a secondary electron imaging, scanning tunnelling microscopy (STM) and electron holography, have been described to show the future development of REM.
TL;DR: In this article, the authors reviewed the progress that has been made from a physicist's perspective, paying attention to the levels of accuracy and precision which are now attainable, and to the advantages and disadvantages of EPMA in relation to other analytical techniques.
Abstract: Electron probe microanalysis (EPMA) is a fairly mature analytical technique which has been widely used in the fields of geochemistry and materials science since the early 1960s. The 1980s and early 1990s or so have seen dramatic improvements, both theoretical and experimental, in the accuracy with which the concentrations of light elements such as oxygen can be measured by EPMA. This has coincided with a resurgence of interest in mixed-valence oxides which was stimulated by the discovery of high temperature superconductivity, and EPMA is now a vital tool for condensed matter physicists working in this field. Stoichiometric characterization is particularly important in the area of thin films, and a great deal of work has been devoted to modifying existing EPMA correction procedures in order to perform analyses of thin film or layered specimens. The present article reviews the progress that has been made from a physicist's perspective, paying attention to the levels of accuracy and precision which are now attainable, and to the advantages and disadvantages of EPMA in relation to other analytical techniques.
TL;DR: Experimental methods for the determination of basic magnetic properties (magnetization, Curie temperature, anisotropy, magnetostriction, and some related quantities) are reviewed in this paper.
Abstract: Experimental methods for the determination of basic magnetic properties (magnetization, Curie temperature, anisotropy, magnetostriction, and some related quantities) are reviewed. The discussion is limited to DC and low-frequency methods, with emphasis on simple and inexpensive experimental equipment and on methods that permit measurements as a function of temperature. Information on the production and measurement of magnetic fields is included.
TL;DR: A review of the progress made in the 1980s in calculations on electron impact excitation of atoms and ions is given for low and intermediate energy ranges in this paper, restricted to advances made in application of the close-coupling approximation, primarily for non-relativistic scattering.
Abstract: A review of the progress made in the 1980s in calculations on electron impact excitation of atoms and ions is given for low and intermediate energy ranges. The review is restricted to advances made in application of the close-coupling approximation, primarily for non-relativistic scattering. The intermediate energy R-matrix method and the coupled-channels optical-potential method have produced very accurate results for hydrogen and helium. Use of pseudostates in the close-coupling expansion is another useful, but less systematic, method for including the effect of continuum channels. For multicharged ions, contributions of excitation-autoionization and resonant-excitation-double-autoionization to total ionization cross sections are important and underscore the role of two-electron correlation effects. Inclusion of such resonance effects is important for an accurate description of all systems as is an accurate description of the target.
TL;DR: In this paper, a general survey of the production and properties of the jets of hadrons that are produced in high-energy collisions of elementary particles is given, and various experimental variables used in the analysis of jets are critically compared, and the results interpreted.
Abstract: This report gives a general survey of the production and properties of the jets of hadrons that are produced in high-energy collisions of elementary particles. Quarks and gluons, the constituents of hadronic particles, never appear directly; the closest one can get to their observation and study is through the jets of hadrons they produce in various types of experiment. The behaviour of these jets is described by the theory of QCD, the relevant points of which are summarized. The fragmentation of jets is understood in terms of various models, which are described. The various experimental variables used in the analysis of jets are critically compared, and used to present the experimental data. The production of jets in different experimental environments is described, and the results interpreted.