Showing papers in "Reviews of Modern Physics in 1985"

Wetting: statics and dynamics

Abstract: The wetting of solids by liquids is connected to physical chemistry (wettability), to statistical physics (pinning of the contact line, wetting transitions, etc.), to long-range forces (van der Waals, double layers), and to fluid dynamics. The present review represents an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.

Surface-enhanced spectroscopy

Abstract: In 1978 it was discovered, largely through the work of Fleischmann, Van Duyne, Creighton, and their coworkers that molecules adsorbed on specially prepared silver surfaces produce a Raman spectrum that is at times a millionfold more intense than expected. This effect was dubbed surface-enhanced Raman scattering (SERS). Since then the effect has been demonstrated with many molecules and with a number of metals, including Cu, Ag, Au, Li, Na, K, In, Pt, and Rh. In addition, related phenomena such as surface-enhanced second-harmonic generation, four-wave mixing, absorption, and fluorescence have been observed. Although not all fine points of the enhancement mechanism have been clarified, the majority view is that the largest contributor to the intensity amplification results from the electric field enhancement that occurs in the vicinity of small, interacting metal particles that are illuminated with light resonant or near resonant with the localized surface-plasmon frequency of the metal structure. Small in this context is gauged in relation to the wavelength of light. The special preparations required to produce the effect, which include among other techniques electrochemical oxidation-reduction cycling, deposition of metal on very cold substrates, and the generation of metal-island films and colloids, is now understood to be necessary as a means of producing surfaces with appropriate electromagnetic resonances that may couple to electromagnetic fields either by generating rough films (as in the case of the former two examples) or by placing small metal particles in close proximity to one another (as in the case of the latter two). For molecules chemisorbed on SERS-active surface there exists a "chemical enhancement" in addition to the electromagnetic effect. Although difficult to measure accurately, the magnitude of this effect rarely exceeds a factor of 10 and is best thought to arise from the modification of the Raman polarizability tensor of the adsorbate resulting from the formation of a complex between the adsorbate and the metal. Rather than an enhancement mechanism, the chemical effect is more logically to be regarded as a change in the nature and identity of the adsorbate.

Ergodic theory of chaos and strange attractors

Abstract: Physical and numerical experiments show that deterministic noise, or chaos, is ubiquitous. While a good understanding of the onset of chaos has been achieved, using as a mathematical tool the geometric theory of differentiable dynamical systems, moderately excited chaotic systems require new tools, which are provided by the ergodic theory of dynamical systems. This theory has reached a stage where fruitful contact and exchange with physical experiments has become widespread. The present review is an account of the main mathematical ideas and their concrete implementation in analyzing experiments. The main subjects are the theory of dimensions (number of excited degrees of freedom), entropy (production of information), and characteristic exponents (describing sensitivity to initial conditions). The relations between these quantities, as well as their experimental determination, are discussed. The systematic investigation of these quantities provides us for the first time with a reasonable understanding of dynamical systems, excited well beyond the quasiperiodic regimes. This is another step towards understanding highly turbulent fluids.

Disordered electronic systems

Abstract: This paper reviews the progress made in the last several years in understanding the properties of disordered electronic systems. Even in the metallic limit, serious deviations from the Boltzmann transport theory and Fermi-liquid theory have been predicted and observed experimentally. There are two important ingredients in this new understanding: the concept of Anderson localization and the effects of interaction between electrons in a disordered medium. This paper emphasizes the theoretical aspect, even though some of the relevant experiments are also examined. The bulk of the paper focuses on the metallic side, but the authors also discuss the metal-to-insulator transition and comment on problems associated with the insulator.

Quantum detection at millimeter wavelengths

Abstract: Photon-assisted tunneling of electrons through an insulating barrier may be used to detect long-wavelength radiation with a sensitivity approaching the limit imposed by the Heisenberg uncertainty principle. A new generation of ultra-low-noise millimeter-wave receivers, currently being developed for astronomical observation, utilizes the extremely sharp nonlinearity produced by single-electron quasiparticle tunneling between two superconductors in a superconductor-insulator-superconductor (SIS) tunnel junction. At millimeter wavelengths, the quantum energy $\frac{\ensuremath{\hbar}\ensuremath{\omega}}{e}$ may be larger than the voltage width for onset of quasiparticle tunneling in a SIS junction; and under these conditions the absorption of a single photon can cause one additional electron to tunnel through the barrier. Several newly discovered quantum effects become possible in this regime, including power amplification of an incoming signal during the process of frequency down-conversion in a heterodyne receiver. The experimental development of SIS millimeter-wave receivers is reviewed, along with the quantum theory of mixing which predicts their performance.

Transport processes during the growth of oxide films at elevated temperature

Abstract: The current understanding of the growth of thermal oxide films in terms of the transport properties of the oxides is reviewed. Emphasis is placed on examining quantitative relationships between the film growth rate and other measurable parameters of the oxides. The theories of film growth which are expected to apply in the extreme limits of thick films (Wagner) and thin films (Cabrera and Mott) are outlined. Particular attention is given to examining the expected limits of validity of these theories and to the various ways in which their predictions can be tested experimentally. The growth of a selection of important oxides is then discussed in the light of these two theories. The examples (CoO, NiO, ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$, ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$, ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, and Si${\mathrm{O}}_{2}$) have been selected such that together they serve to test the theories, have technological relevance, and exhibit a wide variation in behavior. The dominant role of diffusion along oxide grain boundaries in controlling the growth of the crystalline oxides is highlighted.

The ring laser gyro

Abstract: This paper presents a review of both active and passive ring laser devices. The operating principles of the ring laser are developed and discussed, with special emphasis given to the problems associated with the achievement of greater sensitivity and stability. First-principle treatments of the nature of quantum noise in the ring laser gyro and various methods designed to avoid low-rotation-rate lock-in are presented. Descriptions of state-of-the-art devices and current and proposed applications (including a proposed test of metric theories of gravity using a passive cavity ring laser) are given.

Quantum Field Theory Methods and Inflationary Universe Models

Abstract: This paper reviews the theory of inflationary universe models, giving particular emphasis to the question of origin and growth of energy-density fluctuations in these new cosmologies. The first four sections constitute a pedagogical introduction to some of the important quantum field theory methods used in inflationary universe scenarios: calculation of the effective potential, finite-temperature quantum field theory, analysis of the decay of a metastable quantum state, and free field theory in curved space-time.

The quantum effects of electromagnetic fluxes

Abstract: This paper is a review of the problem of the observable action of enclosed electromagnetic fluxes on the quantum-mechanical state of charged particles, known as the Aharonov-Bohm effect. The authors first describe the quantum effects of the fluxes in the quasiclassical approximation, and discuss their relation with basic quantum-mechanical principles. Then they examine the influence of modeling assumptions on the predicted effects of enclosed fluxes. They analyze the experiments demonstrating the reality of the quantum effects of electromagnetic and gravitational fluxes, and finally discuss the physical significance of these quantum effects, comparing the current interpretation, based on the concept of a nonintegrable phase factor, with alternative approaches.

Electron Production in Proton Collisions: Total Cross Sections

Abstract: Existing data on the ionization of neutral atoms and molecules by proton impact are reviewed, and electron production cross-section data are collected. The three major experimental methods are discussed and possible sources of error identified. Some theoretical cross sections are discussed, and well-established methods of relating them to measured cross sections are reviewed. A mathematical equation is fitted to the weighted experimental data for each target, and these fits are adjusted to be consistent with appropriate theoretical calculations and with electron impact and photoionization data. Recommended values of total cross sections for proton-impact ionization are given.

Renormalization theory and ultraviolet stability for scalar fields via renormalization group methods

Abstract: A self-contained analysis is given of the simplest quantum fields from the renormalization group point of view: multiscale decomposition, general renormalization theory, resummations of renormalized series via equations of the Callan-Symanzik type, asymptotic freedom, and proof of ultraviolet stability for sine-Gordon fields in two dimensions and for other super-renormalizable scalar fields. Renormalization in four dimensions (Hepp's theorem and the De Calan--Rivasseau nexclamation bound) is presented and applications are made to the Coulomb gases in two dimensions and to the convergence of the planar graph expansions in four-dimensional field theories (t' Hooft--Rivasseau theorem).

HIGH ENERGY pp AND pp FORWARD ELASTIC SCATTERING AND TOTAL CROSS SECTIONS

Abstract: The present status of elastic pp and pp-bar scattering in the high-energy domain is reviewed, with emphasis on the forward and near-forward regions. The experimental techniques for measuring sigma/sub tot/, rho, and B are discussed, emphasizing the importance of the region in which the nuclear and Coulomb scattering interfere. The impact-parameter representation is exploited to give simple didactic demonstrations of important rigorous theorems based on analyticity, and to illuminate the significance of the slope parameter B and the curvature parameter C. Models of elastic scattering are discussed, and a criterion for the onset of ''asymptopia'' is given. A critique of dispersion relations is presented. Simple analytic functions are used to fit simultaneously the real and imaginary parts of forward scattering amplitudes for both pp and pp-bar, obtained from experimental data for sigma/sub tot/ and rho. It is found that a good fit can be obtained using only five parameters (with a cross section rising as ln/sup 2/s), over the energy range 5 ..infinity are examined critically. The nuclear slope parameters B are also fitted in a model-independent fashion. Examination of the fits reveals a new regularity of the pp-bar and the pp systems.« less

Crystals for quartz resonators

Abstract: On decrit le processus de croissance hydrothermale et on discute des importants defauts dans le quartz et les correlations entre eux. On passe en revue les proprietes du quartz et on donne un tableau des proprietes intrinseques et des proprietes liees aux defauts. Theorie du resonateur et techniques de fabrication. Facteurs de conception du circuit

Rayleigh-Bénard convection and turbulence in liquid helium

Abstract: Recent advances in the understanding of Rayleigh-B\'enard convection and turbulence are reviewed in light of work using liquid helium. The discussion includes both experiments which have probed the steady flows preceding time dependence and experiments which have been directed toward understanding the ways in which turbulence evolves. Comparison is made where appropriate to the many important contributions which have been obtained using room-temperature fluids, and a discussion is given explaining the advantages of cryogenic techniques. Brief reviews are given for recent experimental investigations of convection in $^{3}\mathrm{He}$-$^{4}\mathrm{He}$ mixtures---in both the superfluid and the normal states---and investigations of convection in rotating layers of liquid helium.

Recoil effects in the hyperfine structure of QED bound states

Abstract: The authors give a general discussion of the derivation from field theory of a formalism for the perturbative solution of the relativistic two-body problem. The lowest-order expression for the four-point function is given in terms of a two-particle three-dimensional propagator in a static potential. It is obtained by fixing the loop energy in the four-dimensional formalism at a point which is independent of the loop momentum and is symmetric in the two particle variables. This method avoids awkward positive- and negative-energy projectors, with their attendant energy square roots, and allows one to recover the Dirac equation straightforwardly in the nonrecoil limit. The perturbations appear as a variety of four-dimensional kernels which are rearranged and regrouped into convenient sets. In particular, they are transformed from the Coulomb to the Feynman gauge, which greatly simplifies the expressions that must be evaluated. Although the approach is particularly convenient for the precision analysis of QED bound states, it is not limited to such applications. The authors use it to give the first unified treatment of all presently known recoil corrections to the muonium hyperfine structure and also to verify the corresponding contributions through order ..cap alpha../sup 2/ ln..cap alpha..E/sub F/ in positronium. The requiredmore » integrals are evaluated analytically.« less

Experimental observation of the intermediate vector bosons W + , W − , and Z 0

Abstract: The nobel price lecture of Carlo Rubbia is reprinted. The author recounts the identification of the intermediate vector bosons from the collisions of proton and antiproton beams at CERN.(AIP)

The representation group and its application to space groups

Abstract: A so-called representation (rep) group G is introduced which is formed by all the $|\mathrm{G}|$ distinct operators (or matrices) of an abstract group \ifmmode \hat{G}\else \^{G}\fi{} in a rep space $L$ and which is an $m$-fold covering group of another abstract group g. G forms a rep of \ifmmode \hat{G}\else \^{G}\fi{}. The rep group differs from an abstract group in that its elements are not linearly independent and thus the number $n$ of its linearly independent class operators is less than its class number $N$. A systematic theory is established for the rep group based on Dirac's CSCO (complete set of commuting operators) approach in quantum mechanics. This theory also comprises the rep theory for abstract groups as a special case of $m=1$. Three kinds of CSCO, the CSCO-I, -II, and -III, are defined which are the analogies of ${J}^{2}$, (${J}^{2}$,${J}_{z}$), and (${J}^{2}$,${J}_{z}$,${\overline{J}}_{z}$), respectively, for the rotation group S${\mathrm{O}}_{3}$, where ${\overline{J}}_{z}$ is the component of angular momentum in the intrinsic frame. The primitive characters, the irreducible basis and Clebsch-Gordan coefficients, and the irreducible matrices of the rep group G in any subgroup symmetry adaptation can be found by solving the eigenequations of the CSCO-I, -II, and -III of G, respectively, in appropriate vector spaces. It is shown that the rep group G has only $n$ instead of $N$ inequivalent irreducible representations (irreps), which are just the allowable irreps of the abstract group \ifmmode \hat{G}\else \^{G}\fi{} in the space $L$. Therefore, the construction of the irreps of \ifmmode \hat{G}\else \^{G}\fi{} in $L$ can be replaced by that of G. The labor involved in the construction of the irreps of the rep group G with order $|\mathrm{G}|$ is no more than that for the group g with order $|\mathrm{g}|=\frac{|\mathrm{G}|}{m}$, and thus tremendous labor can be saved by working with the rep group G instead of the abstract group \ifmmode \hat{G}\else \^{G}\fi{}. Based on the rep-group theory, a new approach to the space-group rep theory is proposed, which is distinguished by its simplicity and applicability. Corresponding to each little group G(k), there is a rep group ${\mathbf{G}\ensuremath{'}}_{\mathrm{k}}$. The $n$ inequivalent irreps of ${\mathbf{G}\ensuremath{'}}_{\mathrm{k}}$ are essentially just the acceptable irreps of the little group G(k). Consequently the construction of the irreps of G(k) is almost as easy as that of the little co-group ${\mathbf{G}}_{0}$(k). An easily programmable algorithm is established for computing the Clebsch-Gordan series and Clebsch-Gordan coefficients of a space group simultaneously.

Magnetism in solid He 3 : Confrontation between theory and experiment

Abstract: A summary of the current understanding of nuclear magnetic ordering in solid $^{3}\mathrm{He}$ is presented. The main emphasis is a critical review of what is known from the experiments along with a critique of various theoretical models. Unanswered questions are raised about both the macroscopic phenomena and the microscopic origins of the magnetism. Several experiments are proposed which should help advance our understanding of the magnetic behavior of solid $^{3}\mathrm{He}$.

Breakup phenomena in nuclear collision processes with he projectiles

Abstract: This paper reviews the experimental and theoretical studies of breakup processes induced by He projectiles. For this type of reaction knowledge of three-body kinematics is imperative; hence important aspects are summarized. Although some nuclear structure information has been studied with this type of reaction, the emphasis of this review is mainly on the reaction mechanism. The phenomena described here are quite general, so the consequences for other projectiles (i.e., heavy ions) are also discussed.

Report to The American Physical Society of the study group on radionuclide release from severe accidents at nuclear power plants

Abstract: A detailed analysis is presented of the processes leading to nuclear reactor accidents and their consequences. The various kinds of containment vessels intended to trap radionuclides are discussed.(AIP)

A survey of the alpha-nucleon interaction

Abstract: This paper gives a survey of the alpha-nucleon interaction and then describes experimental work on angular distributions of differential scattering cross sections and polarizations in proton-alpha and neutron-alpha scattering. The phenomenological approach, which includes the study of both local and nonlocal potentials reproducing the experimental alpha-nucleon scattering data, is discussed. Basic studies of the alpha-nucleon interaction attempting to build an interaction between an alpha particle and a nucleon from first principles are then described. The authors then present a critical discussion of the results with some concluding remarks suggesting the direction for further investigation.