Showing papers in "Reports on Progress in Physics in 1981"
TL;DR: Experimental studies on 1/f noise are reviewed with emphasis on experiments that may be decisive in finding the correct theoretical model for this type of noise as discussed by the authors. But the applicability of either theory turns out to be very limited.
Abstract: Experimental studies on 1/f noise are reviewed with emphasis on experiments that may be decisive in finding the correct theoretical model for this type of noise. The experimental results are confronted with two theories: McWhorter's (1959) surface state theory and Clarke and Voss's (1974) theory of local temperature fluctuations. The applicability of either theory turns out to be very limited. The validity of an empirical relation is investigated. Its application to electronic devices proves successful. Experiments show that 1/f noise obeying the empirical relation ( alpha noise) is a fluctuation in the part of the mobility that is due to lattice scattering.
1,057 citations
TL;DR: In this article, a review of surface potentials on natural and artificial bodies in space is presented, with particular emphasis on recent developments, and the effects on charging of nonisotropic plasmas, wakes, and environmental magnetic and electric fields are considered.
Abstract: The subject of surface potentials on natural and artificial bodies in space is reviewed with particular emphasis on recent developments. Following a brief survey of work done up to the early 1970s on the charging of astrophysical objects in interstellar and interplanetary space and spacecraft charging, the various charging mechanisms in space are examined, including the collection of plasma particles, photoemission, and secondary electron emission by electron impact and ion impact, and the effects on charging of nonisotropic plasmas, wakes, and environmental magnetic and electric fields are considered. The concept of equilibrium potential is discussed, along with differential charging, potential barriers and discharge processes. The measurement of spacecraft potentials is then considered, and recent work on spacecraft potential modification and control by active and passive means is presented. Finally, astrophysical applications where charging effects may be important are discussed, and areas for further work are indicated.
972 citations
TL;DR: In this article, the authors review the experimental results observed in the subset of rare-earth systems for which the 4f ions form a lattice with identical valence on each site, and discuss key thermodynamic experiments, such as susceptibility and lattice constant, and spectroscopic experiments such as XPS and neutron scattering.
Abstract: Valence fluctuation phenomena occur in rare-earth compounds in which the proximity of the 4f level to the Fermi energy leads to instabilities of the charge configuration (valence) and/or of the magnetic moment. The authors review the experimental results observed in the subset of such systems for which the 4f ions form a lattice with identical valence on each site. The discussion includes key thermodynamic experiments, such as susceptibility and lattice constant, and spectroscopic experiments such as XPS and neutron scattering. This is followed by a review of existing theoretical work concerning both the ground states and the isomorphic phase transitions which occur in such compounds; the emphasis is on those aspects which make valence fluctuation phenomena such a challenging many-body problem.
707 citations
TL;DR: In this paper, a theory of molecular structure is presented, which demonstrates that the concepts of atoms and bonds may be rigorously defined and given physical expression in terms of the topological properties of the observable distribution of charge for a molecular system.
Abstract: A theory of molecular structure is presented. The theory demonstrates that the concepts of atoms and bonds may be rigorously defined and given physical expression in terms of the topological properties of the observable distribution of charge for a molecular system. As a consequence of these definitions, one in turn obtains a definition of structure and a predictive theory of structural stability. The theory is linked to quantum mechanics by demonstrating that the atoms so defined represent a class of open quantum subsystems with a unique set of variationally defined properties.
445 citations
TL;DR: In this paper, the authors discuss the electronic energy levels of chemical impurities in the classic group IV elemental and the III-V and II-VI compound semiconductors and discuss the experimental results on the spectroscopy of donors and acceptors.
Abstract: Under suitable circumstances imperfections in semiconductors can bind electrons (holes) with a binding energy small compared to the intrinsic energy gap of the host; the wavefunctions characterising the energy levels of the imperfection are extended over many lattice spacings. This review discusses the electronic energy levels of chemical impurities in the classic group IV elemental and the III-V and II-VI compound semiconductors. The large dielectric constant of the host, the anisotropic effective mass tensor and/or the small effective mass of the charge carrier are the factors which play a significant role in the description of the electronic energy levels; they can be viewed as scaled-down versions of the hydrogen atom with bound states having binding energies orders of magnitude smaller than those of the hydrogen atom. The authors present the experimental results on the spectroscopy of donors and acceptors in semiconductors together with the theory necessary for their interpretation. They discuss the experimental results and the theory of the bound states of impurities in the context of the symmetry and the effective-mass parameters of the band extrema with which they are associated. Effects of external perturbation-piezo- and magneto-spectroscopy-are presented both from experimental and theoretical points of view. The review concludes with the experimental observations on the linewidths of the excitation spectra of donors and acceptors in semiconductors and an analysis of the causes underlying them.
397 citations
TL;DR: In this paper, the authors show how new developments in both theory and experiment are beginning to make a major impact on the understanding of electrolyte systems and propose a structural model of these systems.
Abstract: Electrolyte solutions are of importance in a wide range of scientific contexts and as such have attracted considerable theoretical and experimental effort over the years. Nevertheless, there is still no generally agreed structural model of electrolyte solutions. In this review the authors show how new developments in both theory and experiment are beginning to make a major impact on the understanding of these systems.
264 citations
TL;DR: The many theoretical studies of the various magnetic, thermal and magnetoelastic properties for paramagnetic and ferromagnetic transition metals and alloys in the simple itinerant electron model are reviewed in this article.
Abstract: The many theoretical studies of the various magnetic, thermal and magnetoelastic properties for paramagnetic and ferromagnetic transition metals and alloys in the simple itinerant electron model are reviewed. The important amendments to the simple itinerant electron model or Stoner model of magnetism due to the spin wave excitations and spin fluctuations are explained.
260 citations
TL;DR: In this article, a review of the theoretical and practical understanding of non-radiative transitions is presented, with the emphasis on phonon-induced and defect Auger processes.
Abstract: Non-radiative transitions affect many aspects of semiconductor performance. Normally they reduce device efficiency by suppressing luminescence, creating defects, reducing carrier lifetimes, or enhancing diffusion during operation. The present review surveys both the theoretical and practical understanding of non-radiative transitions. It includes general theoretical results and the associated ideas, with the emphasis on phonon-induced and defect Auger processes. Most of the purely formal aspects are omitted, but the points of principle where uncertainties remain are discussed. The review also covers the relation between basic theoretical studies and practical applied work on device degradation. This includes a description of the atomic processes involved in the more important mechanism of device deterioration and the theoretical understanding of the mechanism of these underlying processes. Finally, there is a survey of models proposed for 'killer' centres.
206 citations
TL;DR: In this paper, a review is given of the present situation of electric giant resonances in nuclei, starting with the properties of the well-known electric dipole resonances and summarising the known experimental facts on resonances with other angular momenta and parities.
Abstract: A review is given of the present situation of electric giant resonances in nuclei. Starting with the properties of the well-known electric dipole resonances the authors summarise the known experimental facts on resonances with other angular momenta and parities. They mainly discuss the giant quadrupole and giant monopole resonances which are known best. The difficulties connected with the extraction of nuclear structure information from the experimental cross sections are discussed in detail. They also review the theoretical developments in this field and emphasise especially microscopic models and the corresponding results. As far as possible the experimental facts are compared with the theoretical results.
177 citations
TL;DR: In this article, the vibronic properties of point defects (i.e., impurities and radiation-induced defects) in diamond are discussed. But the authors focus on the point defects where the totally symmetric electron-lattice interaction dominates, cases of dynamic Jahn-Teller distortions, vibronic interactions between nearly degenerate states and a statically deformed defect.
Abstract: Reviews the vibronic properties of point defects (i.e. impurities and radiation-induced defects) in diamond. Cases discussed are: defects where the totally symmetric electron-lattice interaction dominates; cases of dynamic Jahn-Teller distortions; vibronic interactions between nearly degenerate states and a statically deformed defect. Before discussing each of these topics the relevant theory is outlined at an introductory level with the emphasis on features relevant to understanding data. It is shown that a good understanding of the vibronic data is now available in diamond. Compared to defects in silicon, defects in diamond are less prone to static deformations, partly as a result of the high-energy transverse acoustic modes in diamond.
143 citations
TL;DR: The theory and phenomenology of PACAC at the hadron level are reviewed in detail in this paper, and the origins of the Delta I=1/2 rule for non-leptonic hyperon and kaon decays are respectively discussed in the constituent and current-quark bases.
Abstract: The theory and phenomenology of the current algebra-PACAC programme at the hadron level are reviewed in detail. This includes pure PCAC tests, pure current algebra tests, combined tests and hard-pion corrections for hadronic strong, electromagnetic and weak interactions. The programme appears consistent with data in all cases. The theory of chiral symmetry and spontaneous breakdown at the quark level is described and the interplay between the constituent and current-quark pictures is emphasised. The competing models of chiral symmetry breaking and quark masses are presented, compared with data and examined in the context of QCD. The origins of the Delta I=1/2 rule for non-leptonic hyperon and kaon decays are respectively discussed in the constituent and current-quark bases.
TL;DR: The use of self-consistent band calculations to understand the electronic structure of solids is reviewed in this paper, where the formal basis for the approach is first examined to emphasise that not all band calculations are applications of the same theory and critical points, both fundamental and mundane, of the selfconsistency process are examined.
Abstract: The use of self-consistent band calculations to understand the electronic structure of solids is reviewed. The formal basis for the approach is first examined to emphasise that not all band calculations are applications of the same theory. Similarly the critical points, both fundamental and mundane, of the self-consistency process are examined. Again, the central theme is the idea that perhaps some aspects of the self-consistent calculation are not completely established. On the other hand, band structure technique, while still developing, has been rather well explored. Thus one can examine it from the general point of view of seeing what the various techniques imply about the nature of the band structure problem. Finally, some applications of self-consistent band structure calculations are examined.
TL;DR: In this paper, the physics and engineering aspects of the four principal contenders for advanced ground transportation systems using "maglev" and describes the most up-to-date developments in Germany, Japan, USA and the UK in this field.
Abstract: Deals with the physics and engineering aspects of the four principal contenders for advanced ground transportation systems using 'maglev' and describes the most up-to-date developments in Germany, Japan, USA and the UK in this field. Some of the very recent challenging developments in the application of electromagnetic suspension and levitation techniques to contactless bearings are also described.
TL;DR: In this article, it is shown that inertial forces should be generated by the motion of a body relative to the bulk of matter in the universe. But this principle is not contained in general relativity, which leads to a discussion of attempts to derive Machian theories, and the most promising of these appears to be a selection rule for solutions of the general relativistic field equations, in which the space-time metric structure is generated by matter content of the Universe only in a well-defined way.
Abstract: Mach's principle, that inertial forces should be generated by the motion of a body relative to the bulk of matter in the Universe, is shown to be related to the structure imposed on space-time by dynamical theories. General relativity theory and Mach's principle are both shown to be well supported by observations. Since Mach's principle is not contained in general relativity this leads to a discussion of attempts to derive Machian theories. The most promising of these appears to be a selection rule for solutions of the general relativistic field equations, in which the space-time metric structure is generated by the matter content of the Universe only in a well-defined way.
TL;DR: In this article, the most prominent collective degrees of freedom excited in heavy ion reactions are discussed within the framework provided by the natural hierarchy of their characteristic relaxation times, and the limitations of the Lagrangian treatment of heavy-ion reactions are pointed out and a more general approach using transport theory is outlined.
Abstract: The general features of deep inelastic heavy-ion reactions are reviewed. The most prominent collective degrees of freedom excited in these reactions are discussed within the framework provided by the natural hierarchy of their characteristic relaxation times. Both the quantal and classical aspects of these modes are described. The limitations of the Lagrangian treatment of heavy-ion reactions are pointed out, and a more general approach using transport theory is outlined. This latter approach is illustrated by the Langevin, Master and Fokker-Planck equations. The four most widely studied collective modes are then described in detail: the damping of the relative motion; the mass asymmetry degree of freedom; the isobaric charge distribution with isospin fluctuations and giant isovector modes; rotational degrees of freedom.
TL;DR: The present knowledge of the non-equilibrium properties of superconducting microbridges is reviewed from both an experimental and theoretical point of view in this article, where the authors describe the Josephson behavior of super-conducting wires in terms of the resistively shunted junction model and how this behavior manifests itself in experiment.
Abstract: Describes the Josephson behaviour of superconducting microbridges in terms of the resistively shunted junction model and how this behavior manifests itself in experiment. Most of the observed deviations from this model must be treated on the basis of non-equilibrium theories. The present knowledge of the non-equilibrium properties of superconducting microbridges is reviewed from both an experimental and theoretical point of view.
TL;DR: The observations and theory of stellar evolution and supernova explosions give an increasingly refined picture of the origin of supernovae as mentioned in this paper, and recent calculations have given support to the notion that radioactive decay of 56Ni to 56Co to 56Fe determines the exponential light curve and the late-time spectra of Type I supernova (SN I).
Abstract: The observations and theory of stellar evolution and supernova explosions give an increasingly refined picture of the origin of supernovae. Stars evolving singly or in wide binaries probably leave stable white dwarf remnants if their mass is or approximately=70 M(.) are rare, but may have played an important role in galactic nucleosynthesis by exploding via the pair formation process. Recent calculations have given support to the notion that radioactive decay of 56Ni to 56Co to 56Fe determines the exponential light curve and the late-time spectra of Type I supernovae (SN I). The ejection of 0.5-1 M(.) of Ni seems to be required to account for the observations.
TL;DR: In this paper, the authors consider how rotation and magnetism affect the life history of a star from its formation through the main-sequence phases to its post-main-sequence evolution.
Abstract: Reviews the observational evidence for rotation and magnetic fields in stars and discusses the effects of these perturbations on stellar structure and whether the resultant configurations are stable. The authors consider how rotation and magnetism affect the life history of a star from its formation through the main-sequence phases to its post-main-sequence evolution. Theoretical results are compared with observation and some of the many unsolved problems are emphasised. Binary stars or the Sun are not discussed in any detail.
TL;DR: In this article, the production of particles with large transverse momentum in high-energy hadron-hadron collisions is discussed in terms of present theoretical ideas on interactions between hadronic constituents, but no attempt is made to review the theoretical work in a comprehensive manner.
Abstract: The production of particles with large transverse momentum in high-energy hadron-hadron collisions is reviewed. The emphasis is placed on the experimental results. These results are discussed in terms of present theoretical ideas on interactions between hadronic constituents, but no attempt is made to review the theoretical work in a comprehensive manner. It is hoped that the discussion is sufficiently detailed and complete so that non-specialists in the subject can appreciate the main points.
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TL;DR: In this paper, a review is given of work on clusters of galaxies, and it is clearly established that the average mass-to-light ratio (M/L) of galaxy clusters is much larger than that of the visible part of individual galaxies, which suggests the presence of missing mass in clusters.
Abstract: A review is given of work on clusters of galaxies. During the last decade it was clearly established that the average mass-to-light ratio, (M/L), of galaxy clusters is much larger than that of the visible part of individual galaxies, which suggests the presence of missing mass in clusters. Flat outer rotation curves of individual spiral galaxies were discovered, which led to the hypothesis of missing mass in galaxies in the form of dark massive haloes with an R-2 density distribution. But the R-3 density distribution of observed halo tracers, the large range in values of M/L among systems of galaxies with similar galaxy content, and other difficulties with the missing mass hypothesis, admit the possibility that new dynamical physics may be required to resolve the M/L problem. Red-shift surveys for large homogeneous samples of galaxies have led to an improved knowledge of the three-dimensional distribution of galaxies in space. The basic new recognisable large-scale features are superclusters with characteristic sizes approximately 100 Mpc (330 million light years) and equally large galaxy-free voids. The infall velocity of the Local Group towards the Virgo cluster in the Local Supercluster has been measured. More extensive and improved data, as well as the new knowledge of superclustering of galaxies, have strengthened the assumption that galaxy red-shifts are caused by Doppler velocities.
TL;DR: In this article, a review of recent progress in applying quantum gauge field theories to the description of the fundamental forces is presented, starting from the principles of local gauge invariance and spontaneous symmetry breaking to derive the successful Weinberg-Salam model for the weak and electromagnetic interactions and also quantum chromodynamics.
Abstract: In this article we review recent progress in applying quantum gauge field theories to the description of the fundamental forces. We start from the principles of local gauge invariance and spontaneous symmetry breaking to derive the successful Weinberg-Salam model for the weak and electromagnetic interactions and also quantum chromodynamics, the theory of strong interactions. We then discuss grand unified theories in which these theories are combined in a larger structure. Finally, we consider the inclusion of the gravitational interaction through a new symmetry principle, supersymmetry, which relates particles of different spin and whose local realisation includes Einstein’s gravity.
TL;DR: In this paper, an attempt to model the processes underlying the appearance of auroral phenomena as a chain of events beginning with power production and resulting in auroral light emissions is presented.
Abstract: An attempt to model the processes underlying the appearance of auroral phenomena as a chain of events beginning with power production and resulting in auroral light emissions is presented. Power is produced by the interaction of the solar wind with the earth magnetosphere, creating a dynamo effect which is a function of the solar wind speed and the magnitude and orientation of the solar wind magnetic field. The dynamo power generates the convective motion of magnetospheric plasma, and subsequent magnetic-field aligned currents communicate the dynamo power to the polar ionosphere. The currents close as Pederson currents, and the associated Lorentz force accelerates the ionosphere in the direction of the convective motion. An electric potential structure develops at a few thousand km height, forcing current-carrying electrons to flow down the field lines to the ionosphere, where interactions with atmospheric constituents create auroral displays.
Journal Article•
TL;DR: In this paper, a review of the theoretical and practical understanding of non-radiative transitions is presented, with the emphasis on phonon-induced and defect Auger processes.
Abstract: Non-radiative transitions affect many aspects of semiconductor performance. Normally they reduce device efficiency by suppressing luminescence, creating defects, reducing carrier lifetimes, or enhancing diffusion during operation. The present review surveys both the theoretical and practical understanding of non-radiative transitions. It includes general theoretical results and the associated ideas, with the emphasis on phonon-induced and defect Auger processes. Most of the purely formal aspects are omitted, but the points of principle where uncertainties remain are discussed. The review also covers the relation between basic theoretical studies and practical applied work on device degradation. This includes a description of the atomic processes involved in the more important mechanism of device deterioration and the theoretical understanding of the mechanism of these underlying processes. Finally, there is a survey of models proposed for 'killer' centres.