Showing papers in "Physics-Uspekhi in 1973"
TL;DR: The current status of the theory of the electronic structure of polymers containing conjugated bonds is reviewed in this article, where an exact solution of the wave functions of the ground and excited states is found and the exact excitation spectrum is analyzed.
Abstract: The current status of the theory of the electronic structure of polymers containing conjugated bonds is reviewed. Compounds having conjugated bonds have a number of remarkable physical properties, and they occupy a central point in quantum-mechanical studies. The energy of the first optical transition as a function of the molecular length shows unusual behavior. As the molecule is lengthened, the energy of the first transition approaches a finite value called the gap. Hence such a polymer is a semiconductor. A first attempt to explain the gap was based on the hypothesis of spontaneous alternation of bond lengths. The review presents this hypothesis and subjects it to a thorough critique. It has recently been shown that the mechanism that gives rise to the gap in these systems is interaction of electrons and an associated Mott metal-dielectric transition. This conclusion was first based on the unrestricted Hartree-Fock method, and later upon exact solutions for the one-dimensional problem. The article reviews these studies. Polymers with conjugated bonds also show non-trivial magnetic properties, in spite of their lack of d and f electrons. The magnetic properties of these compounds can be described on the basis of the one-dimensional Hamiltonian of Hubbard. Here an exact solution of the wave functions of the ground and excited states is found and the exact excitation spectrum is analyzed. The ground state of these polymers proves to be antiferromagnetic at absolute zero. The spin-wave spectrum begins at zero. Hence these systems show appreciable paramagnetism at finite temperatures. This review analyzes the relation of the paramagnetic susceptibility and the intensity of the EPR signal to the temperature and the polymer length. In conclusion, the review lists problems and questions in the theory of the electronic structure of conjugated polymers that await solution.
149 citations
TL;DR: In this article, the current status of vibrational relaxation in gases and its applications to the theory of molecular lasers is reviewed, and the vibrational energy of diatomic and polyatomic molecules as represented by harmonic-oscillator models is discussed.
Abstract: This article reviews the current status of the theory of vibrational relaxation in gases and its applications to the theory of molecular lasers. We discuss relaxation of the vibrational energy of diatomic and polyatomic molecules as represented by harmonic-oscillator models. The vibrational kinetics in a system of anharmonic oscillators is analyzed in detail. We treat quasi-steady-state population distributions of vibrational levels that arise under substantially non-equilibrium conditions, both in a singlecomponent molecular system and in gas mixtures. We discuss relaxation that proceeds in the presence of sources of vibrationally-excited molecules: infrared resonance radiation, recombination, and dissociation; in particular, we analyze the process of non-equilibrium dissociation at low gas temperatures. We discuss from a unified standpoint based on vibrational kinetics the working mechanisms of lasers using vibrational-rotational transitions in diatomic and polyatomic molecules with various means of excitation (electrical, chemical, and gas-dynamic).
121 citations
TL;DR: In this article, a method for consistent analysis of a quantum-mechanical system situated in a potential that depends periodically on the time, for example, in the field of a strong classical electromagnetic wave is considered.
Abstract: A method is considered for consistent analysis of a quantum-mechanical system situated in a potential that depends periodically on the time, for example, in the field of a strong classical electromagnetic wave The emission of such a system is considered, and particularly the shift of the fundamental frequency ω' and the appearance of satellites ω' ± hω
91 citations
TL;DR: In this article, a review of the status of problems involving the interaction of matter and optical-band electromagnetic radiation of intensity such that any medium becomes a fully ionized plasma is presented.
Abstract: A review is presented of the status of problems involving the interaction of matter and optical-band electromagnetic radiation of intensity such that any medium becomes a fully ionized plasma. The following are considered within the framework of the single-electron approximation in the case of nonrelativistic energies: stimulated bremsstrahlung and absorption of an electron in the field of a strong electromagnetic wave, stimulated two-photon Compton scattering, and scattering of electrons in the field of an intense standing electromagnetic wave (the Kapitza-Dirac effect). The role played by these processes in the heating of plasma by laser radiation is analyzed, as is the question of the possibility of obtaining amplification (negative absorption) of light in transitions in a continuous spectrum. The bibliography is brought up to date to the middle of 1971.
81 citations
TL;DR: A survey of the present state of the theory of rotational Brownian motion is given in this article, where the probability distributions for the orientations of Brownian particles are written in terms of generalized spherical functions, which are matrix elements of irreducible representations of the rotation group.
Abstract: A survey of the present state of the theory of rotational Brownian motion is given. Chapters 1 and 2 expound the theory of rotational diffusion and the solution of the problem of rotational random walks. The probability distributions for the orientations of Brownian particles are written in terms of generalized spherical functions, which are matrix elements of irreducible representations of the rotation group. Methods are discussed for the experimental determination of the nature of Brownian rotation by the use of nuclear magnetic resonance, dielectric relaxation, and the Rayleigh scattering of light. Chapter 3 gives an exposition of generalized rotational diffusion, taking account of inertial effects in the Brownian motion. The influence of inertial effects on dielectric magnetic relaxation and on the scattering of light is discussed. The conclusion of the review gives a discussion of precession effects in Brownian motion.
74 citations
TL;DR: In this article, a modified diffusion approximation of the Fokker-Planck equation was proposed to study the impact-radiation recombination in a low-temperature plasma, taking into account the real energy structure of the atom, the influence of the radiative transitions, and the relationship between the non-equilibrium distributions of the atoms over the levels and of the electrons over the energies.
Abstract: The theory of impact-radiation recombination (ionization) in a low-temperature plasma is based on the representation of this process as a random walk of a recombining (released) electron in the discrete space of the atom's energy levels. Different methods of studying recombination (ionization) are considered. The described modified diffusion approximation, combining the possibilities of the previously developed approaches, takes into account the real energy structure of the atom, the influence of the radiative transitions, and the relationship between the non-equilibrium distributions of the atoms over the levels and of the electrons over the energies. A solution is presented for the Fokker-Planck equation expressed in finite-difference form, and analytic expressions are obtained for the ionization and recombination coefficients. The results are compared with the published experimental data.
60 citations
TL;DR: In this article, the theory of a number of phenomena occurring in a plasma situated in a strong high-frequency field is reviewed, including nonlinear penetration and reflection of electromagnetic waves from a plasma, stationary nonlinear waves, and spreading and contraction of a plasma layer under the influence of the pressure of a high frequency field.
Abstract: The article reviews the theory of a number of phenomena occurring in a plasma situated in a strong high-frequency field. The analysis is based on a relatively simply hydrodynamic collisionless plasma model. Principal attention is paid to the stability of the plasma in the strong high-frequency field. A single dispersion equation is used to consider different modifications of parametric instabilities (decay instabilities, parametric resonance, transparent-plasma instability of the stimulated scattering type). Also discussed are a number of problems in the equilibrium and dynamics of a plasma in a strong high-frequency field, particularly nonlinear penetration and reflection of electromagnetic waves from a plasma, stationary nonlinear waves, and spreading and contraction of a plasma layer under the influence of the pressure of a high-frequency field.
52 citations
48 citations
TL;DR: In this paper, a review deals with various variants of classification of the types of secondary emission of light by molecules; cases are distinguished in which the secondary emission occurs without additional processes that find their way between photon emission and absorption; the advisability of differentiating between the cases of resonance fluorescence and resonance scattering is noted.
Abstract: The review deals with various variants of classification of the types of secondary emission of light by molecules; cases are distinguished in which the secondary emission occurs without additional processes that find their way between photon emission and absorption; the advisability of differentiating between the cases of resonance fluorescence and resonance scattering is noted. Reference is made to papers that have made contributions to the development of quantum-mechanical and classical theory of Raman scattering and to the development of the concepts of the relations between electron-vibrational absorption spectra, fluorescence spectra, and scattering excitation near and near and far resonance. Conditions are considered of excitation of the spectrum at different relations between the electronic-oscillator damping constant, the atom vibration frequency, the rotational frequencies, and the difference between the frequency of the incident light and the frequency of the electronic transition. The conditions for the excitation of typical light scattering, typical resonance fluorescence, and certain intermediate types, in which individual features of scattering are combined with certain features of fluorescence (phenomena of the transition type) are noted. The results of investigations of different models of the scattering centers, their advantages, shortcomings, and limits of applicability are compared. The most interesting results of the experimental investigations of resonant scattering of light by molecules and crystals are noted.
46 citations
TL;DR: In this paper, two-quantum transitions in Molecules and Molecular Crystals were studied and two-photon Absorption in Semiconductors and Ionic Crystals.
Abstract: CONTENTS 1. Introduction 299 2. General Relations for Two-Photon Transitions 299 3. Experimental Technique 301 4. Two-Quantum Transitions in Molecules and Molecular Crystals 302 5. Two-Photon Absorption in Semiconductors and Ionic Crystals 308 References 318
42 citations
TL;DR: In this paper, the authors present an overview of the properties of the crystal structure and band structure of optical and Galvanomagnetic properties, as well as antifriction properties.
Abstract: TABLE OF CONTENTS 1. Introduction 728 2. Crystal Structure 728 3. Optical Properties and Band Structure 732 4. Electrical and Galvanomagnetic Properties 734 5. Antifriction Properties 738 6. Conclusions 739 Bibliography 740
TL;DR: In this article, the main types of interference are subdivided into four groups, called pulsed beats, beat resonance, parametric resonance, and phase resonance, common to all these phenomena is the appearance of modulations in the spontaneous emission of the atoms or in the absorption coefficient of the atomic system.
Abstract: The research on optical phenomena connected with interference of nondegenerate atomic states is reviewed. The main types of phenomena are subdivided into four groups, called pulsed beats, beat resonance, parametric resonance, and phase resonance. Common to all these phenomena is the appearance of modulations in the spontaneous emission of the atoms or in the absorption coefficient of the atomic system. Certain nonlinear manifestations of interference of states are also considered. The possibility of using interference phenomena as methods for the investigation of subtle details of the energy structures of atoms and molecules is considered.
TL;DR: In this article, the main condition under which the medium exerts a strong influence on the mechanical properties of the body (in cases of reversible adsorption interaction not connected with dissolution, corrosion, or other chemical processes) is that the solid and the medium be of related nature, to make the surface energy low on the boundary between the liquid and solid phases.
Abstract: The fact that deformation and failure are facilitated by the reversible physico-chemical influence of the medium has been established by now for all types of solids: for metals (and also certain covalent crystals) in contact with liquid metals, for ionic crystals and inorganic glasses in the presence of molten salts, water, alcohol, or other polar media, and for molecular crystals of organic compounds in contact with nonpolar and low-polarity organic liquids. In general these phenomena facilitate the breaking and realignment of the interatomic bonds in the presence of certain foreign atoms or molecules (which have sufficient mobility to ensure their penetration into the bond-breaking zone) and can be described as a lowering of the free surface energy of the given solid under the influence of the surrounding medium. The main condition under which the medium exerts a strong influence on the mechanical properties of the body (in cases of reversible adsorption interaction not connected with dissolution, corrosion, or other chemical processes) is that the solid and the medium be of related nature, to make the surface energy low on the boundary between the solid and liquid phases. At the same time, the form and degree of manifestation of these effects depend in a complicated manner on the real structure of the body (defects) and on the deformation conditions (stresses, temperature, strain rate, time of contact, etc.) An optimal combination of these factors makes it possible to use the influence of the medium to facilitate dispersion and treatment, particularly of solid materials that are difficult to work. To the contrary, by eliminating individual factors that lower the strength by adsorption it becomes possible to protect against the influence of the medium.
TL;DR: In this paper, it is shown that the use of the Laue criterion is based on an error in the very formulation of the question, and that the results of the Jones-Richards experiments do not contradict this.
Abstract: The question of the form of the momentum-energy tensor of the electromagnetic field (in a medium) remains debatable to this day. The dilemma of whether the photon momentum in a medium is equal to nhν/c (Minkowski) or hν/nc (Abraham) therefore remains unresolved (n is the refractive index). Simple considerations based on the law governing the motion of the center of gravity of the "field + medium" system lead, however, to a unique choice of Abraham's tensor. The Jones-Richards experiments do not contradict this, although they do not lead to a solution of the problem. In principle, measurements of the Jones-Richards type (of the pressure of light in media) in the pulsed regime would yield the solution of the problem. Considerable space is allotted to an analysis of the question of the "rejection" of Abraham's tensor, a question advanced by Laue and supported by many authors. It is shown that the use of the Laue criterion is based on an error in the very formulation of the question. The arguments advanced in this connection are illustrated by using as an example analogous relations in the case of the motion of a simple static system, namely a charged capacitor. The conservations laws applied to a static electromagnetic field having angular momentum also lead to Abraham's expression for the field momentum density.
TL;DR: In this article, the scale invariance of the interactions of high-energy particles and nuclei is discussed, and the results and the difficulties encountered in the calculations are considered, and special attention is devoted to interactions with targets of the light nuclei d, t, He3, and He4.
Abstract: High energy nuclear physics has important purely scientific value and applied value. Statistical methods of calculation based on the intranuclear cascade model permit agreement to be obtained with the known experimental data over the entire energy range above several tens of MeV. For energies T 3–5 BeV it is necessary to take into account the change in the density of intranuclear matter with development of the cascade of particles inside the target-nucleus; in the transition to the very high energy region it is necessary to take into account also many-particle interactions in which several fast particles collide with one nucleon at the same time. The methods of calculation are discussed briefly, and the results and the difficulties encountered in the calculations are considered. Special attention is devoted to interactions with targets of the light nuclei d, t, He3, and He4. Scale invariance of the interactions of high-energy particles and nuclei is discussed.
TL;DR: In this paper, the spectral transport of the mean-squared vorticity in the field of quasi-two-dimensional turbulence in the upper layer of the ocean is analyzed.
Abstract: The possibility of distinguishing between turbulence and wave fluctuations of the hydrodynamic fields is discussed. Possible mechanisms of generation of turbulence in the ocean are considered, and theoretical information as well as experimental data are given concerning the spectra of small-scale turbulence in the upper layer of the ocean. Intermittent turbulence in the main body of the ocean is described. The laws governing the turbulent diffusion in the ocean are briefly considered. A hypothesis is advanced concerning the spectral transport of the mean-squared vorticity in the field of quasi-two-dimensional turbulence. The small-scale convection produced by the difference between the diffusion coefficients of heat and salt in sea water is considered. Experimental data are presented on the vertical thin-layer microstructure of the ocean, and possible mechanisms whereby it is generated are considered, such as shear instability, internal waves, lateral convection, and differences between the diffusion coefficients for momentum, heat, and salt. The distortions produced in the internal-wave spectra by the presence of vertical thin-layer microstructure are analyzed.
TL;DR: The problem of reconstructing the spatial structure of biological macromolecules and their aggregates (e.g., in viruses and crystals) from electron micrographs, which are two-dimensional projections of these three-dimensional objects, is treated in this paper.
Abstract: The problem is treated of reconstructing the spatial structure of biological macromolecules and their aggregates (e.g., in viruses and crystals) from electron micrographs, which are two-dimensional projections of these three-dimensional objects. Potentialities of the physical methods (optical diffraction, filtering, and holography) in interpreting electron micrographs are described. The fundamentals are given of the mathematical theory of three-dimensional reconstruction from projections: the Fourier method, the algebraic methods, and the analytical methods. Applications are reviewed of the three-dimensional reconstruction methods in studying a number of objects: protein crystals, helical structures made of globular proteins, bacteriophages, and spherical viruses.
TL;DR: In this article, a review is devoted to exposition of the physical principles on which the current ideas on plasma turbulence are based, and a comparison is made of the results obtained in the theory of plasma turbulence and the turbulence of incompressible liquids.
Abstract: The review is devoted to exposition of the physical principles on which the current ideas on plasma turbulence are based. A comparison is made of the results obtained in the theory of plasma turbulence and the turbulence of incompressible liquids. The basic physical differences between hydrodynamic and plasma turbulence are pointed out. It is shown how the concepts of turbulent excitations arise in the statistical description of turbulence. The fundamental difference is pointed out between turbulent elementary excitations and elementary excitations describing a state close to thermodynamic equilibrium. Special emphasis is given to explanation of the physical meaning of the concept of effective turbulent collisions. It is shown that inclusion of turbulent collisions does not make possible construction of a theory of weak turbulence on the basis of simple expansions of the interaction in the turbulence energy. Examples are presented which show that effective turbulent collisions can fundamentally change the theoretical predictions which must be compared with existing experiments. It is shown how the inclusion of effective turbulent collisions permits construction of a theory of correlation functions of turbulent plasma fields. In connection with the discussion of new approaches to the theory of weak turbulence, taking into account effective turbulent collisions, an analysis is carried out of the theories of anomalous electrical conductivity of a plasma in an external electric field.
TL;DR: In this article, a description of the theoretical ideas on the relation between the nucleon-antinucleon and nucleon nucleon interactions is given, which make it possible to organize the experimental data on the elastic scattering of nucleons into a picture of the forces which act between the nucleus and antinucleons.
Abstract: The current data on scattering and annihilation of nonrelativistic antinucleons are reviewed. A description is given of the theoretical ideas on the relation between the nucleon-antinucleon and nucleon-nucleon interactions, which make it possible to organize the experimental data on the elastic scattering of nucleons into a picture of the forces which act between the nucleon and antinucleon. The main conclusion from the existing experimental facts and theoretical considerations is that we should expect a strong attraction due to the exchange of a neutral vector meson (the omega meson) in the nucleon-antinucleon system at distances of the order of 1–2 F. Calculations show that this attraction leads to the existence of bound and resonant nuclear-like states in the nucleon-antinucleon system, which should manifest themselves experimentally as heavy mesons of mass close to the mass of two nucleons (quasinuclear mesons). The lifetime of such mesons is determined by the probability of the annihilation process (which occurs at small distances of the order of the nucleon Compton wavelength and consequently has a small effect on the production of the quasinuclear state). A distinctive feature of quasinuclear mesons is their comparatively large probability of decay (virtual or real) into the nucleon-antinucleon channel. For this reason, the production of quasinuclear mesons should be seen in collisions of antinucleons with protons and nuclei. Another characteristic consequence of the existence of quasinuclear mesons is an anomalous energy dependence of the cross section for annihilation of slow antinucleons. The theoretical predictions are in agreement with the latest experimental results, which are discussed in detail in the paper.
TL;DR: In this paper, the results in ferromagnetic domain theory have been presented and a detailed description of those properties of the domain structure that are independent of the properties of a model is given.
Abstract: This article presents in detail those results in ferromagnetic domain theory that have been obtained recently and have not previously appeared in monographs or reviews. A significant part of the article is devoted to consideration of basic problems of the theory. A detailed description is given of those properties of the domain structure that are independent of the properties of the model. As concrete examples, the domain structures in uniaxial and cubic ferromagnets are considered. Experimental results are cited only by way of illustration. Some generally accepted ideas have proved wrong and are subjected to criticism in this article.
TL;DR: In this paper, a review is given of the theoretical investigations of the rotation, in a magnetic field, of the plane of polarization of infrared electromagnetic waves traversing nonmagnetic semiconductors with cubic crystal lattices.
Abstract: A review is given of the theoretical investigations of the rotation, in a magnetic field, of the plane of polarization of infrared electromagnetic waves traversing nonmagnetic semiconductors with cubic crystal lattices. It is shown that in the range of wavelengths corresponding to the interband or intraband optical absorption the Faraday effect can be used to determine the energy gaps, reduced effective masses, and the spectroscopic bandsplitting factor. At longer wavelengths corresponding to the free-carrier absorption the Faraday effect can yield the average effective mass at the Fermi level and the Fermi energy can be found at low temperatures and in strong magnetic fields. Uniaxial deformation of crystals with many-valley bands makes it possible to use the free-carrier Faraday effect in the determination of the mass averaged out over an energy ellipsoid as well as the transverse component of the effective mass. A review is also given of the experimental results published for germanium, silicon, indium antimonide, gallium arsenide, and lead chalcogenides, which are optically isotropic in the absence of an external magnetic field.
TL;DR: In this paper, the Percus-Yevick Equation (PYE) was used to solve the problem of self-consistency of the liquid pressure in a system of hard spheres.
Abstract: CONTENTS1. Introduction 592 a) Problem of the Theory of the Liquid State 592 b) The Method of Integral Equations 593 2. The Percus-Yevick Equation 594 a) Functional Definition of the Direct Correlation Function 594 b) The Percus Approximation 595 c) Analytic Solution of the Percus-Yevick Equation for a System of Hard Spheres 597 3. Results of Numerical Calculations by the Integral Equation Method 599 a) Calculation of the RDF and of the Thermodynamic Characteristics 599 b) Determination of the Interparticle Potential 603 c) Problem of Self Consistency of the Liquid Pressure 604 d) Phase Transitions in the Percus-Yevick Theory 605 Bibliography 606
TL;DR: In this paper, the authors introduce the concept of equilibrium thermal-conduction modes and nonequilibrium and other modes, including shockwave and thermal-wave modes, and discuss their properties.
Abstract: CONTENTS I. Introduction 688 H. Shock-wave modes 689 III. Equilibrium thermal-conduction modes 691 IV. Nonequilibrium and other modes 701 References 706