This paper reviews the progress made in the last few years in theoretical understanding of the properties of superconductors in very high magnetic fields. The key ingredient in the new understanding is the recognition that the usual negative effect of orbital frustration in a superconducting state, reflected in diamagnetic pair breaking, is obviated when all electrons reside in only the few lowest Landau levels. A new relation between the superconducting order parameter and the magnetic field now exists which permits a strong enhancement of the critical temperature with increasing magnetic field. The issue of Pauli pair breaking and the effect of impurities in this new state are also discussed, along with the important observation that the attractive component of the effective electron-electron interaction in systems with low carrier density is enhanced with increasing magnetic field. While this paper emphasizes the theoretical aspects of this high-field limit, it does present a unified picture of superconductivity throughout the whole temperature and magnetic-field phase diagram. Numerical applications to simple models of low-carrier-density semiconductors and semimetals are also discussed, since these materials are the most likely candidates for this new phase.

The Nambu—Jona-Lasinio model is reviewed in its flavor SU(2) and SU(3) versions applied to quarks. The dynamical generation of quark masses is demonstrated as a feature of chiral symmetry breaking. One finds that the associated meson spectra, as well as the meson static properties, can be well described. Current-algebra results, which arise as a consequence of symmetry considerations, automatically hold for this model and are explicitly demonstrated to do so. These include the Goldberger-Treiman and Gell-Mann-Oakes-Renner relations. Effects of finite temperature, finite chemical potential, and strong Maxwell and chromoelectromagnetic fields on the dynamically generated quark mass and the meson spectra are discussed. The alternative procedure of bosonization to obtain an effective Lagrange density in mesonic degrees of freedom, using the derivative expansion, is also presented. The current status in relating the results of this model to that of chiral perturbation theory is critically examined.

Together with the pendulum, the symmetric and asymmetric rotors are standard models, well studied in both classical and quantum physics. In the limit of high angular momentum $J$, the quantum problem of an asymmetric rotor approaches the classical limit, which is characterized by one unstable and two stable motions. Rotations with respect to the axes with maximum and minimum moments of inertia are stable, while the rotations about the intermediate axis are unstable. Upon diagonalization of the rotor's Hamiltonian at fixed $J$, most eigenvectors are seen to be localized around the directions of maximum and minimum moment of inertia. The asymmetric rotor displays in this regard localization similar to that in many atomic and nuclear few-body systems, wherein external interactions mix degenerate states, particularly at high excitation. Indeed, there is a complete one-to-one correspondence between the rotor and these systems, with the principal ($n$) and angular momentum ($l$) quantum numbers mapping onto $J$, and its azimuthal projection $M$, respectively, for the rotor. Localization at a maximum or a saddle point of a potential is of considerable significance in a variety of problems.

The authors offer a historical and pedagogical introduction to the local-field problem in dielectrics. They then discuss a microscopic approach to the problem and introduce momentum dependence. Finally they apply these results to electron-phonon coupling in quasi-two-dimensional systems, in particular the high-$T_c$ superconductors.

Hydrogen interactions with imperfections in crystalline metals and semiconductors are reviewed. Emphasis is given to mechanistic experiments and theoretical advances contributing to predictive understanding. Important directions for future research are discussed.

A review is given of our present knowledge of collective spin-isospin excitations in nuclei. Most of this knowledge comes from intermediate-energy charge-exchange reactions and from inelastic electron- and proton-scattering experiments. The nuclear-spin dynamics is governed by the spin-isospin-dependent two-nucleon interaction in the medium. This interaction gives rise to collective spin modes such as the giant Gamow-Teller resonances. An interesting phenomenon is that the measured total Gamow-Teller transition strength in the resonance region is much less than a model-independent sum rule predicts. Two physically different mechanisms have been discussed to explain this so-called quenching of the total Gamow-Teller strength: coupling to subnuclear degrees of freedom in the form of $\Delta$-isobar excitation and ordinary nuclear configuration mixing. Both detailed nuclear structure calculations and extensive analyses of the scattering data suggest that the nuclear configuration mixing effect is the more important quenching mechanism, although subnuclear degrees of freedom cannot be ruled out. The quenching phenomenon occurs for nuclear-spin excitations at low excitation energies ($\omega \sim 10-20$ MeV) and small-momentum transfers ($q\le 0.5$ ${\mathrm{fm}}^{-1\mathrm{}}$). A completely opposite effect is anticipated in the high ($\omega$, $q$)-transfer region ($0\le \omega \le 500$ MeV, $0.5\le q\le 3$ ${\mathrm{fm}}^{-1\mathrm{}}$). The nuclear spin-isospin response might be enhanced due to the attractive pion field inside the nucleus. Charge-exchange reactions at GeV incident energies have been used to study the quasifree peak region and the $\Delta$-resonance region. An interesting result of these experiments is that the $\Delta$ excitation in the nucleus is shifted downwards in energy relative to the $\Delta$ excitation of the free proton. The physical origin of this shift is discussed, and it is shown that it may be related to the energy-dependent, attractive one-pion exchange interaction in the medium.

All known data on the energy distribution of secondary electrons from collisions of protons with atoms and molecules have been reviewed and differential cross sections have been collected. The two experimental methods used to obtain the data are discussed and possible sources of error pointed out. Theoretical treatments are reviewed and several methods of checking the consistency of the data are discussed. Two semiempirical models have been chosen to represent the differential cross sections, and parameters for these models are given which fit the average of the experimental data, subject to known constraints. Recommended values of differential cross sections are given for ten target gases by means of these models.

This article reviews the discovery, exploration, and application of negative-ion resonances in inelastic electron scattering by molecules adsorbed on surfaces. A major theme of the review is the degree to which the properties of resonances in free molecules are perturbed by adsorption. The influence of the surface upon the energy, lifetime (width), symmetry, and decay channels of molecular resonances is discussed, in the light of both experimental and theoretical studies of a wide range (from diatomic molecules to polymers) of both weakly bound (physisorbed) and strongly bound (chemisorbed) molecules. The metallic image potential, electron scattering by the atoms of the surface, and chemical bonding in chemisorption systems are found to be key factors in determining the energy, width, and symmetry of resonances in molecular adsorbates. In the case of oriented adsorbed molecules, the angular distribution of scattered electrons is found to reflect not only the symmetry of the resonant state (as in the gas phase), but also the orientation of the molecular axis. Coherent elastic electron scattering by the surface can modulate the angular distributions, as well as the shape of the resonance profile. Selection rules that govern the observed resonance behavior are discussed. A further consequence of adsorption is the enrichment of the range of channels into which resonances may decay, and the excitation of both molecule-surface and intermolecular vibrational modes has been established. The article concludes with an evaluation of future prospects for the investigation and application of resonances in adsorbed molecules.

Within the last decade, significant progress has been made towards a consistent and complete reformulation of the Copenhagen interpretation (an interpretation consisting in a formulation of the experimental aspects of physics in terms of the basic formalism; it is consistent if free from internal contradiction and complete if it provides precise predictions for all experiments). The main steps involved decoherence (the transition from linear superpositions of macroscopic states to a mixing), Griffiths histories describing the evolution of quantum properties, a convenient logical structure for dealing with histories, and also some progress in semiclassical physics, which was made possible by new methods. The main outcome is a theory of phenomena, viz., the classically meaningful properties of a macroscopic system. It shows in particular how and when determinism is valid. This theory can be used to give a deductive form to measurement theory, which now covers some cases that were initially devised as counterexamples against the Copenhagen interpretation. These theories are described, together with their applications to some key experiments and some of their consequences concerning epistemology.

This paper provides a theoretical framework for the high-precision (≤1%) electroweak experiments that are likely to be done in the next ten years. The authors have collected the Standard Model (SM) predictions of 14 weak neutral-current observables and 15 $W$ and $Z$ properties to the one-loop level and have calculated the deviations that would be caused by ten general types of possible new physics that enter at the tree or loop level. Certain experiments appear to have special promise as probes of the new physics considered here. Most importantly, a systematic procedure is introduced that provides a prescription for the analysis of future experimental data and the means of delineating the nature of new physics if quantitative deviations from SM predictions are observed.

The fundamental theory of the geometric phase is summarized in a way suitable for use in molecular systems treated by the Born-Oppenheimer approach. Both Abelian and non-Abelian cases are considered. Applications discussd include the Abelian geometric phase associated with an intersection of two electronic potential-energy surfaces; screening of nuclei by the electrons from an external magnetic field; non-Abelian gauge potentials in molecular systems with Kramers degeneracy; and the coupling between different electronic levels (Born-Oppenheimer breakdown) represented as a gauge potential. Experimental tests for these systems are discussed, as well as a number of experiments on spin systems.

Bak, Tang, and Wiesenfeld proposed the idea of self-organized criticality in order to gain a general understanding of the behavior of extended dynamical systems driven in a nonequilibrium state. In particular this idea was intended to explain the ubiquitous scaling behavior and fractal structures that are observed in many different phenomena occurring spontaneously in nature. Recent experiments on the dynamics of a pile of sand, which had been expected to show self-organized criticality, are reviewed and it is shown that sand behaves in a manner more reminiscent of a first-order transition than of a second order (or critical) one.

A common thread is followed through diverse phenomena: Weak interactions lock seemingly independent variables into a collective state of enhanced or depressed energy. A rather novel perspective is thus afforded on superconductivity and on nuclear and particle physics.

In 1962 Bienenstock and Ewald described a simple and systematic method for computing all the crystallographic space groups in Fourier space. Their approach is reformulated and further simplified, starting from the definition of the point group of a structure as the set of operations that take it into something indistinguishable and not merely identical to within a translation. The reformulation does not require periodicity, making it possible to define and compute on an equal footing the space groups for crystals, quasicrystals, and incommensurately modulated structures, without having to digress into the crystallography of unphysically many dimensions, and using only simple geometry and the most elementary properties of symmetry groups. The general scheme is illustrated by a unified computation of all the icosahedral, cubic, orthorhombic, monoclinic, and triclinic space groups. The remaining (axial) crystallographic and quasicrystallographic space groups have been discussed in a companion paper.

DUMAND is a project to build a Deep Underwater Muon And Neutrino Detector offshore near the island of Hawaii. At present under construction, it hopes to inaugurate the field of high-energy neutrino astronomy. Potential sources of high-energy neutrinos are listed, and estimates of neutrino intensity given. The paper is concerned with the physics, technology, and history of the project, which started informally in 1973. It survived through a series of summer conferences until it was funded as a feasibility study in 1979 and established in the Hawaii DUMAND Center, at the University of Hawaii. Over a dozen collaborating groups have contributed to the successful construction and operation of DUMAND I, the SPS or Short Prototype String, which established the benign character of the ocean environment and demonstrated its suitability for DUMAND II, a 216-phototube array now under construction. DUMAND II, recently funded, will have more than 20 times the area of any existing detector and a mass of almost 2 million tons; this size is minimal for the intensities and cross sections anticipated. The project became feasible—both technically and financially—through important technical advances in data transmission via fiber optics, high-speed computer technology, special photomultiplier tubes made by Hamamatsu and Philips, remotely controlled undersea vehicles with manipulative abilities, and many deep-sea electronic and oceanographic components. It is supported by an international collaboration with 15 collaborating institutions in the U.S., Europe, and Japan. It is scheduled to install a three-string test array (TRIAD) by late 1992, and the complete nine-string array is scheduled for operation in late 1993.

There are currently proposals to test the weak equivalence principle for antimatter by studying the motion of antiprotons, negative hydrogen ions, positrons, and electrons under gravity. The motions of such charged particles are affected by residual gas, radiation, and electric and magnetic fields, as well as gravity. The electric fields are particularly sensitive to the state of the "shielding" container. This paper reviews, and extends where necessary, the physics of these extraneous influences on the motion of charged particles under gravity. The effects considered include residual gas scattering; wall potentials due to patches, stress, thermal gradients, and contamination states; and image-charge-induced dissipation.

Planar systems admit quantum states that are neither bosons nor fermions, i.e., whose angular momentum is neither integer nor half-integer. After a discussion of some examples of familiar models in which fractional spin may arise, the relevant (nonrelativistic) quantum mechanics is developed from first principles. The appropriate generalization of statistics is also discussed. Some physical effects of fractional spin and statistics are worked out explicitly. The group theory underlying relativistic models with fractional spin and statistics is then introduced and applied to relativistic particle mechanics and field theory. Field-theoretical models in 2+1 dimensions are presented which admit solitons that carry fractional statistics, and are discussed in a semiclassical approach, in the functional integral approach, and in the canonical approach. Finally, fundamental field theories whose Fock states carry fractional spin and statistics are discussed.