Showing papers in "Physics-Uspekhi in 2000"

The Sagnac effect: correct and incorrect explanations

Abstract: Different explanations for the Sagnac effect are discussed. It is shown that this effect is a consequence of the relativistic law of velocity composition and that it can also be explained adequately within the framework of general relativity. When certain restrictions on the rotational velocity are imposed, the Sagnac effect can be attributed to the difference in the time dilation (or phase change) of material particle wave functions in the scalar (or correspondingly vector) gravitational potential of the inertial forces in a rotating reference system for counterpropagating waves. It is also shown that all the nonrelativistic interpretations of the Sagnac effect, which are unfortunately sometimes found in scientific papers, monographs and textbooks, are wrong in principle, even though the results they yield are accurate up to relativistic corrections in some special cases.

Two-dimensional ferroelectrics

Abstract: The investigation of the finite-size effect in ferroelectric crystals and films has been limited by the experimental conditions. The smallest demonstrated ferroelectric crystals had a diameter of ~200 A and the thinnest ferroelectric films were ~200 A thick, macroscopic sizes on an atomic scale. Langmuir–Blodgett deposition of films one monolayer at a time has produced high quality ferroelectric films as thin as 10 A, made from polyvinylidene fluoride and its copolymers. These ultrathin films permitted the ultimate investigation of finite-size effects on the atomic thickness scale. Langmuir–Blodgett films also revealed the fundamental two-dimensional character of ferroelectricity in these materials by demonstrating that there is no so-called critical thickness; films as thin as two monolayers (1 nm) are ferroelectric, with a transition temperature near that of the bulk material. The films exhibit all the main properties of ferroelectricity with a first-order ferroelectric–paraelectric phase transition: polarization hysteresis (switching); the jump in spontaneous polarization at the phase transition temperature; thermal hysteresis in the polarization; the increase in the transition temperature with applied field; double hysteresis above the phase transition temperature; and the existence of the ferroelectric critical point. The films also exhibit a new phase transition associated with the two-dimensional layers.

Quasi-two-dimensional turbulence

Abstract: We review the results of numerical and experimental studies in quasi-two-dimensional (Q2D) turbulence. We demonstrate that theoretical energy spectra with slopes –5/3 and –3 (Kraichnan–Batchelor–Leith) can be observed only for a special set of external parameters. The bottom drag, beta effect, finite Rossby–Obukhov radius or vertical stratification, which distinguish geophysical Q2D turbulence from its purely 2D counterpart, determine the organization of a Q2D flow on a large scale. Since the spectral energy flux in 2D turbulence is directed upscale, the bottom friction takes on a special role. In the absence of bottom drag the energy condenses on the largest resolvable scale and flow equilibration is not attained.

High-temperature superconductivity: the current state

Abstract: Theoretical and experimental work concerning high-temperature superconductors in general and cuprates in particular is reviewed. A detailed analysis of the current knowledge of the subject suggests that when in the normal state, superconducting cuprates behave very much the same as 'conventional' metals. Experimental evidence is presented for the existence of strong relaxation processes in the normal state of HTSC systems at low energy. Ab initio calculations of the optical spectra and the electron–phonon interaction (EPI) show that the electron-phonon mechanism explains many features of low-energy relaxation processes in HTSC systems, including the high critical temperature. However, many properties of the superconducting state, for example, the anisotropic d pairing in cuprates, cannot be explained with the EPI mechanism alone. A number of models for cuprate superconductors with EPI and Coulomb repulsion are discussed in detail.

Order–disorder transformations and phase equilibria in strongly nonstoichiometric compounds

Abstract: Data on order–disorder phase transformations in strongly nonstoichiometric carbides and nitrides MXy (X=C, N) of Group IV and V transition metals at temperatures below 1300–1400 K are reviewed. The order-parameter functional method as applied to atomic and vacancy ordering in strongly nonstoichiometric MXy compounds and to phase equilibrium calculations for M–X systems is discussed. Phase diagram calculations for the Ti–C, Zr–C, Hf–C, V–C, Nb–C, Ta–C, Ti–N, and Ti–B–C systems (with the inclusion of the ordering of nonstoichiometric carbides and nitrides) and those for pseudobinary carbide M(1)C–M(2)C systems are presented. Heat capacity, electrical resistivity and magnetic susceptibility changes at reversible order–disorder phase transformations in nonstoichiometric carbides are considered.

The evolution of large clusters under the action of ultrashort superintense laser pulses

Abstract: The evolution of large clusters exposed to a superintense ultrashort laser pulse is considered. Cluster excitation results from the interaction of its electron subsystem with the laser field. Multiple ionization and X-ray emission followed by explosion in clusters irradiated by a laser field are investigated. The increase of the electron temperature in this process and of the charge of the cluster ion are discussed. The reabsorption of photons in such a plasma is found to be relatively small. The optimal conditions are analyzed for efficient absorption of laser radiation by large clusters. This absorption occurs on the surface of the cluster only. The review is done of the works devoted to X-ray emission and generation of high harmonics of the incident radiation from a hot cluster ion. The optical density of the cluster plasma is found to be relatively small for resonance photons of multiply charged atomic ions produced inside the cluster. Expansion and decay of the cluster during and after the laser pulse are discussed.

Electron cooling: 35 years of development

Abstract: The electron cooling technique for shrinking ion beams of extremely high phase-space density was proposed and first tested at the Nuclear Physics Institute of the Siberian Branch of the Russian Academy of Sciences. The present review traces the history of the development of the idea from its first emergence in 1965 and the discussion originated in G I Budker's talk at the symposium on electron–positron rings in Sacle in September 1966 — through 35 years of research — down to the present time, with numerous applications in many acceleration centers around the world.

Quantum mechanics: new experiments, new applications, and new formulations of old questions

Abstract: Some of the quantum mechanical conceptual problems, their current status, and related theoretical developments are reviewed. The characteristics of the entangled quantum states are analyzed, and new experiments and quantum information applications involving such states are discussed. The well-known paradox of Schroedinger's cat (the impossibility of observing superpositions of macroscopically distinct states that are predicted by quantum mechanics) is discussed. It is shown that decoherence (arising when a quantum system is measured in such a way that some information about its state is recorded in its environment) prevents the distinguishing of a superposition and the corresponding mixture. This overcomes the difficulties associated with the paradoxical nature of quantum measurement provided we remain within the framework of the theory of open systems. Other conceptual difficulties, while actually lying outside physics, are now the subject of much research and have already led to new interesting interpretations of quantum mechanics. The suggestion of Wigner and others that the observer's consciousness be included in the theory of quantum measurement is discussed in this context. A hypothesis is put forward which might enable the functioning of consciousness to be described in quantum measurement terms.

Order and correlations in genomic DNA sequences. The spectral approach

Abstract: The structural analysis of genomic DNA sequences is discussed in the framework of the spectral approach, which is sufficiently universal due to the reciprocal correspondence and mutual complementarity of Fourier transform length scales. The spectral characteristics of random sequences of the same nucleotide composition possess the property of self-averaging for relatively short sequences of length M≥100–300. Comparison with the characteristics of random sequences determines the statistical significance of the structural features observed. Apart from traditional applications to the search for hidden periodicities, spectral methods are also efficient in studying mutual correlations in DNA sequences. By combining spectra for structure factors and correlation functions, not only integral correlations can be estimated but also their origin identified. Using the structural spectral entropy approach, the regularity of a sequence can be quantitatively assessed. A brief introduction to the problem is also presented and other major methods of DNA sequence analysis described.

Self-sustained volume discharge

Abstract: The state-of-the-art in the physics of large-volume high-power gas discharges is reviewed. The characteristic properties and distinguishing features of high-pressure self-sustained discharges are discussed, existing experimental data are presented, and major formation and contraction models are considered. It is shown that the lower bound on the volume discharge ignition voltage is due to the onset of cathode instability. Relationships between the discharge parameters at the glowing and power delivery stages are analyzed. Record discharge characteristics are presented and difficulties involved in resolving a comprehensive theory of the volume discharge are pointed out.

Universal viscosity growth in metallic melts at megabar pressures: the vitreous state of the Earth's inner core

Abstract: Experimental data on and theoretical models for the viscosity of various types of liquids and melts under pressure are reviewed. Experimentally, the least studied melts are those of metals, whose viscosity is considered to be virtually constant along the melting curve. The authors' new approach to the viscosity of melts involves the measurement of the grain size in solidified samples. Measurements on liquid metals at pressures up to 10 GPa using this method show, contrary to the empirical approach, that the melt viscosity grows considerably along the melting curves. Based on the experimental data and on the critical analysis of current theories, a hypothesis of a universal viscosity behavior is introduced for liquids under pressure. Extrapolating the liquid iron results to the pressures and temperatures at the Earth's core reveals that the Earth's outer core is a very viscous melt with viscosity values ranging from 102 Pa s to 1011 Pa s depending on the depth. The Earth's inner core is presumably an ultraviscous (>1011 Pa s) glass-like liquid — in disagreement with the current idea of a crystalline inner core. The notion of the highly viscous interior of celestial bodies sheds light on many mysteries of planetary geophysics and astronomy. From the analysis of the pressure variation of the melting and glass-transition temperatures, an entirely new concept of a stable metallic vitreous state arises, calling for further experimental and theoretical study.

Critical points of condensation in Coulomb systems

Abstract: The critical points of condensation in Coulomb systems are described here by a modified van der Waals equation of state taking into account a many-particle exchange interaction between virtual atoms with overlapping classically accessible spheres of valence electrons. A characteristic feature of the Coulomb critical points is strong electron – ion coupling caused by the proximity to the metal – insulator transition. We consider a cell model of the exchange interaction of virtual atoms and examples of Coulomb critical points in a system of charged hard spheres, in alkali metals, in metal – ammonia solutions, and in excitonic systems. The Coulomb critical point parameters of transition metals are determined. We consider examples of insulator – metal transitions in semiconducting and dielectric fluids which form the Coulomb systems only in the liquid phase, and discuss a semiconducting critical state of mercury.

The mechanism of lightning attraction and the problem of lightning initiation by lasers

Abstract: Physical processes determining the ability of lightning to change its trajectory by choosing high constructions to strike are discussed. The leader mechanism of lightning propagation is explained. The criterion for a viable ascending (upward) leader to originate from a construction is established. The mechanism of the weak long-distance interaction between the ascending counter leader originating from a grounded construction and the descending (downward) leader from a cloud is analyzed. Current problems concerning lightning protection and lightning triggering by a laser spark are discussed, the latter being of special interest owing to a recent successful experiment along this line.

Two electron problem and the nonlocal equations of electrodynamics

Abstract: A survey is offered for the current knowledge of nonlocal electrodynamic equations which in some cases (e.g., in solving boundary value problems in optics) can replace Maxwell's equations. The nonlocal equations are derived using the semi-classical or quantum-electrodynamic approaches. The former involves an expansion of retarded potentials in appropriate parameters and a subsequent transition, to terms of order v2/c2, to quantum mechanical operators in the Lagrangian of a system of moving charges. The latter approach is to consider second- and third-order quantum electrodynamic effects for two hydrogen-like atoms arbitrarily far apart. Various nonlocal equations are derived for the propagation of photons and electromagnetic waves in spin systems, dielectrics, and metals, taking into account a variety of quantum transitions and intermediate states in the spectrum of the interacting atoms. By combining nonlocal field equations with relevant constitutive equations, a number of typical boundary-value optical problems are solved for semi-infinite media, superthin films, and for objects whose linear dimensions are much smaller than the light wavelength.

Regular variation of the fine structure of statistical distributions as a consequence of cosmophysical agents

Abstract: Considered is the statistical ground of the certainty of cosmophysical effects on the fine structure of distributions governing the results of measurements in various physical processes. We show that the previously discussed effects of synchronous variations of histogram shapes in independent processes, and the periodical occurrence of histograms of a particular shape, do not depend on the form of the integral distribution. The adequacy of visual (expert) estimation when comparing the shapes of histograms as an alternative to the standard statistical methods is justified.

Nanotribology: experimental facts and theoretical models

Abstract: Nanotribology is a new physical discipline in which friction, adhesion, wear and lubrication are studied within a unified framework at the nanoscopic level. In this paper, the experimental and theoretical problems of topical interest in this field are reviewed. In the analysis of the experimental data, emphasis is placed on 'dry' adhesive friction between the probe of a scanning frictional microscope and an atomically smooth surface. On the theoretical side, studies related to the mechanisms of adhesive (static) and dynamic (velocity proportional) friction are discussed and results on the electromagnetic, electron, and phonon effects as well as molecular dynamics results are presented. Studies using the method of quartz crystalline microbalance and the 'surface force' concept are briefly reviewed.

Superconductivity: the day before yesterday — yesterday — today — tomorrow

Abstract: This talk is devoted to the history of the study of superconductivity and the prospects of further research in this field.

The origin of life and thinking from the viewpoint of modern physics

Abstract: Attempts at a physical picture of how living creatures emerge from nonliving matter are beset with difficulties due to a low probability of some of the stages of the process. It is shown that these difficulties arise from the misconstruction of the term 'coding' and that they are overcome by assuming that the polynucleotide catalized rather than 'coded' the formation of protein in primary organisms (hypercycles). A realistic scenario including the emergence of a unified code is considered for such a process. A physical mechanism of thinking and the basis of a necessary evolutionary change are discussed, for which purpose the concepts of information, valuable information, and information generation are analyzed. It is shown that thinking reduces largely to pattern recognition. A possible molecular mechanism of recognition is considered which is shown to be quite likely to have appeared in the course of evolution.

Metastable and bistable defects in silicon

Abstract: Existing data on the properties and structure of metastable and bistable defects in silicon are analyzed. Primary radiation-induced defects (vacancies, self-interstitial atoms, and Frenkel pairs), complexes of oxygen, carbon, hydrogen, and other impurity atoms and defects with negative correlation energy are considered.

Spinning relativistic particles in external fields

Abstract: The motion of spinning relativistic particles in external electromagnetic and gravitational fields is considered. The noncovariant spin formalism is crucial for the correct description of the influence of the spin on the particle trajectory. It is shown that the true coordinate of a relativistic spinning particle is the naive, common coordinate r. A simple derivation is presented for the gravitational interaction of first order in spin, for a relativistic particle. The equations of motion obtained for a relativistic spinning particle in an external gravitational field differ essentially from the Papapetrou equations. Effects of higher order in spin are discussed, including the gravimagnetic moment, a special spin effect in general relativity. We consider also the contributions of the spin interactions of first and second order to the gravitational radiation of compact binary stars.

Climate as a problem of physics

Abstract: The logical fundamentals of the theory of climate are outlined: (1) the climate system OLA (ocean–land–atmosphere) is defined; (2) analogously to the theory of turbulence, the notion of climate is defined as a multicomponent random function in the OLA space-time (or, equivalently, as a statistical ensemble of states the OLA system passes through in a period of several decades); (3) the solar climate, i.e. the distribution of solar radiation at the upper atmosphere boundary, is determined, to be employed as the boundary condition for the OLA system; (4) the 'horizontal' heat and mass transfer processes between the equatorial and polar zones are described; (5) the 'vertical' processes of radiative–convective heat and mass transfer, among them the greenhouse effect of water vapor and small gas admixtures, are discussed; (6) the 'vertical' radiative heat transfer processes in an aerosol-containing atmosphere is considered, including the anti-greenhouse effect of volcanic and smoke aerosols, and the 'nuclear night' and 'nuclear winter' scenarios.

Diffraction and diffraction radiation

Abstract: Similarities and differences between two closely related phenomena, diffraction and diffraction radiation, are discussed in the context of a scalar theory.

Vortex ring oscillations, the development of turbulence in vortex rings and generation of sound

Abstract: The state of the art in describing the eigen-oscillations of a vortex ring in an ideal incompressible fluid is reviewed. To describe eigen-oscillations, the displacement field is taken as the basic dynamic variable. A vortex ring with the simplest vorticity distribution in the core and with a potential flow in the vortex ring envelope is the commonest approximation used in treating the eigen-oscillations of vortex rings of a more general form. It turns out that allowing for even a very weak degree of core smoothing causes many oscillation modes to lose their stability. It is shown that the instability effect is determined by the sign of the vibration energy. The energies of the ring eigen-oscillations are calculated and two kinds of eigen-oscillations, those with a negative energy and those with a positive energy, are identified, of which it is the former which become unstable when the core vorticity is smoothed. The multiple instabilities of vortex ring oscillations together with the details of the spatial structure of its eigen-oscillations suggest that it is the nonlinear evolution of precisely these processes which might be the origin of vortex ring turbulence. A new method for the study of unsteady processes in turbulent vortex rings, which utilizes the experimental diagnostics of the ring's sound field, is presented. The structure of the sound field strongly supports the proposed model of the turbulent vortex ring.

Thermodynamic fluctuations within the Gibbs and Einstein approaches

Abstract: A comparative analysis of the descriptions of fluctuations in statistical mechanics (the Gibbs approach) and in statistical thermodynamics (the Einstein approach) is given. On this basis solutions are obtained for the Gibbs and Einstein problems that arise in pressure fluctuation calculations for a spatially limited equilibrium (or slightly nonequilibrium) macroscopic system. A modern formulation of the Gibbs approach which allows one to calculate equilibrium pressure fluctuations without making any additional assumptions is presented; to this end the generalized Bogolyubov – Zubarev and Hellmann – Feynman theorems are proved for the classical and quantum descriptions of a macrosystem. A statistical version of the Einstein approach is developed which shows a fundamental difference in pressure fluctuation results obtained within the context of two approaches. Both the 'genetic' relation between the Gibbs and Einstein approaches and the conceptual distinction between their physical grounds are demonstrated. To illustrate the results, which are valid for any thermodynamic system, an ideal nondegenerate gas of microparticles is considered, both classically and quantum mechanically. Based on the results obtained, the correspondence between the micro- and macroscopic descriptions is considered and the prospects of statistical thermodynamics are discussed.

Physical principles of the generalized Boltzmann kinetic theory of gases

Abstract: This paper addresses the fundamental principles of generalized Boltzmann physical kinetics, which introduces terms accounting for the variation of the distribution function over times of the order of the collision time into the Boltzmann equation. The paper is primarily aimed at clarifying the qualitative aspects of the theory whose mathematical formalism was developed in the author's earlier work. There is a detailed discussion of how the generalized Boltzmann equation obtained by the multiscale method relates to other alternative approaches used in the development of kinetic equations. The application of the generalized Boltzmann equation to certain classical transport processes is discussed.