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Showing papers on "Field (physics) published in 1979"




Journal ArticleDOI
L. W. Davis1
TL;DR: In this paper, a relatively simple method for calculating the properties of a paraxial beam of electromagnetic radiation propagating in vacuum is presented, where the vector potential field is assumed to be plane-polarized.
Abstract: A relatively simple method for calculating the properties of a paraxial beam of electromagnetic radiation propagating in vacuum is presented. The central idea of the paper is that the vector potential field is assumed to be plane-polarized. The nonvanishing component of the vector potential obeys a scalar wave equation. A formal solution employing an expansion in powers of $\frac{{w}_{0}}{l}$ is obtained, where ${w}_{0}$ is the beam waist and $l$ the diffraction length. This gives the same result for the lowest-order components of the transverse and longitudinal electric field of a Gaussian beam that was derived by Lax, Louisell, and McKnight using a more complicated approach. We derive explicit expressions for the second-order transverse electric field and the third-order longitudinal field corrections.

559 citations


Journal ArticleDOI
TL;DR: The well-known electromagnetic fields generated by infinitesimal dipoles in the presence of the earth are reviewed briefly with special reference to contributions by H. Bremmer as discussed by the authors.
Abstract: The well-known electromagnetic fields generated by infinitesimal dipoles in the presence of the earth are reviewed briefly with special reference to contributions by H. Bremmer. The fields due to currents in extended conductors can be expressed in terms of an integral over the occupied volume but its evaluation is possible only when the currents are known in their dependence on the properties of the earth. This is true of the horizontal-wire antenna quite close to the earth both when driven by a localized emf and when acting as a scatterer in an incident field. It is also true of horizontal antennas in the earth not too close to the surface. Expressions for the most useful component of the radiated or scattered field are formulated for an end-driven Beverage-type antenna, for the horizontal wire as a scatterer in the presence of the earth, and for the embedded insulated traveling-wave antenna.

466 citations


Journal ArticleDOI
TL;DR: In this article, an intertwining operator is constructed that explicitly expresses the bilocal two-singleton field in terms of one-particle massless fields, and the theory remains self-consistent and unitary to lowest order in the coupling Fields describing states of one or two singletons, with the attendant interesting gauge problems.
Abstract: Gauge-invariant wave equations for massless fields with fixed, but arbitrary, integer spin have been constructed Extended to include interactions with external sources, the theory remains self-consistent and unitary to lowest order in the coupling Fields describing states of one or two singletons, with the attendant interesting gauge problems, are studied An intertwining operator is constructed that explicitly expresses the bilocal two-singleton field in terms of one-particle massless fields

358 citations


Journal ArticleDOI
TL;DR: In this article, the constraints arising upon coupling a massless spin 5 2 field to gravity are analyzed, and they depend not only on the Einstein tensor, but also on the off-shell (Weyl) components of the curvature.

289 citations


Journal ArticleDOI
R. M. Fleming1, C. C. Grimes1
TL;DR: In this paper, the authors observed that nonlinear resistance is observed only after a well-defined threshold field is reached and that electric fields above the threshold result in noise in the potential difference across a current biased specimen.
Abstract: Two new effects associated with Fr\"ohlich sliding-mode conductivity have been observed in Nb${\mathrm{Se}}_{3}$ First, nonlinear resistance is observed only after a well-defined threshold field is reached Second, electric fields above the threshold result in noise in the potential difference across a current biased specimen We interpret the threshold field as direct evidence of charge-density wave depinning and the noise as a result of charge-density wave motion

282 citations


Journal ArticleDOI
TL;DR: In this article, the authors used simultaneous auroral and equatorial electric field data along with magnetic field data to study anomalous electric field patterns during disturbed times, showing that during some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern.
Abstract: Simultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low latitude ionosphere. These currents flow westward across the dayside. In several cases the zonal equatorial electric field component was nearly identical in form to the zonal auroral component, indicating the close electrical coupling between these regions. Less certain, but equally intriguing, is the evidence presented for a close relationship between the zonal equatorial electric field and the time derivative of the ring current induced magnetic field. Another class of events seems related to rapid changes of magnetospheric convection and a temporary imbalance between the field external to the plasmasphere and the shielding charges in the Alfven layer. Examples of both rapid increases and decreases are presented. The latter seems oftern to be related to a northward turning of the interplanetary magnetic field.

276 citations


Journal ArticleDOI
J. Hubbard1
TL;DR: In this paper, a previously developed theory of the magnetism of iron, based upon the notion of a randomized exchange field, is modified and extended, which allows one to take into account these fields, which are found to change the details of the previous results without affecting the main conclusions.
Abstract: A previously developed theory of the magnetism of iron, based upon the notion of a randomized exchange field, is modified and extended. It is shown that Coulomb fields arise in association with the randomized exchange field; the modification allows one to take into account these fields, which are found to change the details of the previous results without affecting the main conclusions. The theory has been extended to calculate the properties of the model at finite temperatures: the Curie temperature (1840 K), the magnetization curve, the paramagnetic susceptibility (a Curie-Weiss law), and the effective interatomic exchange coupling are calculated for iron. The magnitudes of the atomic spin moments were found to vary little up to 1.5 times the Curie temperature.

227 citations



Journal ArticleDOI
TL;DR: In this paper, the E and F region drift velocities have been used to look for correlations between changes in equatorial electric fields and the interplanetary magnetic field (IMF), which is not always true; the IMF may reverse without any apparent effect at the equator, and large equatorial field perturbations are sometimes observed when the IMF B/sub z/ is large and southward but not varying drastically.
Abstract: Radar measurements of E and F region drift velocities have been used to look for correlations between changes in equatorial electric fields and the interplanetary magnetic field (IMF). The east-west component of the IMF appears to be unimportant, but the north-south component has some effect; rapid reversals from south to north are sometimes correlated with reversals of the equatorial east-west electric field during both daytime and nighttime. This is not always true, however; the IMF may reverse without any apparent effect at the equator. Furthermore, large equatorial field perturbations are sometimes observed when the IMF B/sub z/ is large and southward but not varying drastically. In this latter case the equatorial perturbations start nearly simultaneously with the onset of auroral substorms, while in the previous case they usually correlate with the onset of the substorm recovery phase. These observations indicate that the IMF does not affect the equatorial electric fields directly. Rather, it is changes in the magnetospheric electric fields and the auroral zone electric field and conductivity distribution (which may or may not be triggered by IMF changes) which alter the worldwide ionospheric current flow and electric field pattern, of which the equatorial observations are an indication.

Journal ArticleDOI
TL;DR: The selfconsistent field approximation for coupled-vibron systems in the semiclassical limit yields Hartree-type equations, in which only the eigenenergies and turning points are self-consistently evaluated as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, it was shown that a field satisfying the Yang-Mills equations in dimension 4 with a point singularity is gauge equivalent to a smooth field if the functional is finite.
Abstract: We show that a field satisfying the Yang-Mills equations in dimension 4 with a point singularity is gauge equivalent to a smooth field if the functional is finite. We obtain the result that every Yang-Mills field overR 4 with bounded functional (L 2 norm) may be obtained from a field onS 4=R 4∪{∞}. Hodge (or Coulomb) gauges are constructed for general small fields in arbitrary dimensions including 4.

Journal ArticleDOI
TL;DR: In this paper, the authors present a general self-consistent nonlinear theory of the FEL process, which results in a set of coupled differential equations governing the spatial evolution of the amplitudes and wavelength of the radiation and space charge fields.
Abstract: The development of lasers in which the active medium is a relativistic stream of free electrons has recently evoked much interest. The potential advantages of such free-electron lasers include, among other things, continuous frequency tunability, very high operating power, and high efficiency. The free-electron laser (FEL) is characterized by a pump field, for example, a spatially periodic magnetic field which scatters from a relativistic-electron beam. The scattered radiation has a wavelength much smaller than the pump wavelength, depending on the electron-beam energy. The authors present a general self-consistent nonlinear theory of the FEL process. The nonlinear formulation of the temporal steady-state FEL problem results in a set of coupled differential equations governing the spatial evolution of the amplitudes and wavelength of the radiation and space-charge fields. These equations are readily solved numerically since the amplitude and wavelength vary on a spatial scale which is comparable to a growth length of the output radiation. A number of numerical and analytical illustrations are presented, ranging from the optical to the submillimeter-wavelength regime. Our nonlinear formulation in the linear regime is compared with linear theory, and agreement is found to be excellent. Analytical expressions for the saturated efficiency and radiation amplitude are alsomore » shown to be in very good agreement with our nonlinear numerical solutions. Efficiency curves are obtained for both the optical and submillimeter FEL examples with fixed magnetic-pump parameters. It is shown that these intrinsic efficiencies can be greatly enhanced by appropriately contouring the magnetic-pump period. In the case of the optical FEL, the theoretical single-pass efficiency can be made greater than 20% by appropriately decreasing the pump period and increasing the pump magnetic field.« less

Journal ArticleDOI
TL;DR: In this paper, measurements of dc electric fields, field-aligned currents, the plasma density, and wave electric fields and density fluctuations have been made for the first time at auroral zone altitudes between 1000 and 8000 km on the S3-3 satellite.
Abstract: Measurements of dc electric fields, field-aligned currents, the plasma density, and wave electric fields and density fluctuations have been made for the first time at auroral zone altitudes between 1000 and 8000 km on the S3-3 satellite. The design and operation of the various detectors that made these measurements is described, and some typical scientific results are presented. These include the observations that the high altitude auroral zone plasma density is typically 5–50 particles/cm³, that field-aligned currents exceeding the electrostatic ion cyclotron instability threshold are often observed in regions of ion cyclotron wave emission and accelerated upgoing ions, that the auroral zone electric field penetrates the plasmapause to cause deviations from corotation of the plasmasphere, and that the energetic electron high latitude trapping boundary is sometimes equatorward of the last closed magnetic field line, as determined by the reversal in the poleward electric field component.

Journal ArticleDOI
TL;DR: In this article, Lagrangians for massless free fields with arbitrary spins are derived by postulating gauge transformations for these fields, and global supersymmetry field variations are then exhibited for a massless system involving the pair of spins (S,S+ 1 2 ).

Journal ArticleDOI
TL;DR: In this article, the quantum defect-theory treatment of an electron in the Coulomb field surrounding an ionic core is recast in a form largely independent of field characteristics and thus applicable, e.g., to square wells or to the Morse fields of diatomic molecules.
Abstract: The quantum-defect-theory (QDT) treatment of an electron in the Coulomb field surrounding an ionic core is recast in a form largely independent of field characteristics and thus applicable, e.g., to square wells or to the Morse fields of diatomic molecules. The reformulation parallels Seaton's classification of alternative Coulomb-field wave functions, and makes it applicable to other fields. Wronskians of alternative pairs of base functions have an important role in the theory. For electron energies $\ensuremath{\epsilon}l0$ in a Coulomb field these Wronskians reduce to trigonometric functions of $\ensuremath{ u}={(\ensuremath{-}2\ensuremath{\epsilon})}^{\ensuremath{-}\frac{1}{2}}$, familiar in the QDT; other fields lead to trigonometric functions of different arguments. Quantum defects are generalized to eigenvalues of a reaction matrix, as in Seaton's work, but this matrix can now be calculated even below threshold energies with the introduction of a "smooth" Green's function appropriate to QDT applications.

Journal ArticleDOI
TL;DR: In this article, the energy spectrum of an electron in the presence of a uniform magnetic field and a potential of hexagonal symmetry is analyzed, and two alternative approaches are used, one that takes as a basis set free-electron Landau functions, and a second one that treats an effective single-band Hamiltonian with the Peierls substitution.
Abstract: The energy spectrum of an electron in the presence of a uniform magnetic field and a potential of hexagonal symmetry is analyzed. Two alternative approaches are used, one that takes as a basis set free-electron Landau functions, and a second one that treats an effective single-band Hamiltonian with the Peierls substitution. Both methods lead to consistent results. The energy spectrum is found to have recursive properties similar to those discussed by Hofstadter for the case of a square lattice. The density of states over each subband of the spectrum has the same structure as that for the original field-free band. The plot of integrated density of states versus field is also discussed.


Journal ArticleDOI
TL;DR: In this paper, a combined-source solution for electromagnetic radiation and scattering from a perfectly conducting body is developed for a three-dimensional closed surface S, which is then applied to a surface of revolution.
Abstract: A combined-source solution is developed for electromagnetic radiation and scattering from a perfectly conducting body. In this solution a combination of electric and magnetic currents, called the combined source, is placed on the surface S of the conducting body. The combined-source operator equation is obtained from the E -field boundary-value equation. It is shown that the solution to this operator equation is unique at all frequencies. The combined-field operator equation also has a unique solution, but it is not directly applicable to the aperture radiation problem. The H -field and E -field operator equations fail to give unique solutions at frequencies corresponding to the resonant frequencies of a cavity formed by a hollow conductor of the same shape. The combined-source operator equation is solved by the method of moments. The solution, valid for a three-dimensional closed surface S , is then applied to a surface of revolution. Examples of numerical computations are given for a sphere, a cone-sphere, and a finite circular cylinder.

Journal ArticleDOI
TL;DR: In this article, the steady state equations for current conservation were solved numerically by assuming (1) several divided regions of the global earth (such as the polar cap, auroral zone, and middle-low latitudes), (2) exponentially distributed anisotropic electric conductivities for each zone with a continuous change at the boundaries of the regions, and (3) exponential distributed downward and upward field-aligned current intensities in the auroral region, assumptions based on our current knowledge of auroral phenomena and geomagnetic variations as well as rocket and satellite measurements of field-
Abstract: Computer simulation studies of the electric fields and currents in the global ionosphere produced by field-aligned electric currents for quiet periods are conducted. The steady state equations for current conservation are solved numerically by assuming (1) several divided regions of the global earth (such as the polar cap, auroral zone, and middle-low latitudes), (2) exponentially distributed anisotropic electric conductivities for each zone with a continuous change at the boundaries of the regions, and (3) exponentially distributed downward and upward field-aligned current intensities in the auroral region, assumptions based on our current knowledge of auroral phenomena and geomagnetic variations as well as rocket and satellite measurements of field-aligned currents. Resultant computer-plotted diagrams include equipotential contours of the electric fields, vector distributions of the electric fields and currents, and electric current patterns equivalent to the magnetic field effect produced by the field-aligned and real ionospheric currents. One of the merits of this simulation method is that the three-dimensional current system can roughly be estimated from the equivalent current system obtained from ground-based geomagnetic data alone. This paper also provides a foundation for a similar study of substorms. The following main results are obtained: (1) Conductivity inhomogeneity alters considerably the electric field pattern that has previously been obtained by assuming the uniform conductivity distribution. (2) Even a slight conductivity enhancement along the nightside auroral belt results in a large modification of the electric field. (3) The existence of the strong conductivity gradients and the field-aligned currents in the equatorward half of the auroral oval reduces the electric field in the middle and low latitudes. This corresponds to the ‘shielding’ effect of the electric field inside the Alfven layer in the magnetotail. (4) Seasonal changes in the polar cap conductivities cause surprisingly large effects on the electric fields and currents. (5) The equivalent ionospheric currents differ significantly from real ionospheric currents in both intensity and direction.

Journal ArticleDOI
TL;DR: In this article, the Einstein field equations and conservation equations linearized around a most general (astrophysically relevant) spherically symmetric space-time are reduced to a set of equations for gauge-invariant geometrical objects defined on the two-dimensional timelike submanifold spanned by the radial and time coordinates.
Abstract: The Einstein field equations and the conservation equations linearized around a most general (astrophysically relevant) spherically symmetric space-time are reduced to a set of equations for gauge-invariant geometrical objects defined on the two-dimensional timelike submanifold spanned by the radial and time coordinates. Odd-parity metric and matter perturbations are each expressed in terms of a vector field, matter perturbations in terms of an additional scalar field on this submanifold. Even-parity perturbations are expressed in terms of a symmetric tensor field and a scalar field for the metric and in terms of two scalars, a vector, and a symmetric tensor field for matter. The odd-parity vectorial perturbations are derivable from a single master scalar equation, and their junction conditions across the surface of a collapsing star are given.

Journal ArticleDOI
TL;DR: In this paper, a balloon-borne electric field meter was used to measure the electric field at the ground and at the top of the corona, and it was shown that the field a hundred metres above the ground is several times larger than the ground field.
Abstract: Intense electric fields beneath thunderstorms produce electrical discharges (coronae) at the tips of trees, bushes and other sharp objects attached to the surface of the earth. We find typical corona current densities of about 1 nA m−2 in an 8 kV m−1 field at the ground. The ions released into the air limit the magnitude of the field at the ground to about 10kV m−1. Our measurements beneath thunderstorms with a balloon-borne electric field meter show that the magnitude of the field a hundred metres above the ground is several times larger than at the ground; in one case the field 300 metres above ground was 6 times that at the ground. The substantial thickness of the space charge layer and the speed with which it vanishes when the electric field strength declines imply that the charge carriers have substantial velocities (0.4m s−1) either because their mobilities are high or because they are carried by air motions. Coronae also influence the time behaviour of the electric field at the ground. The field at the ground often changes very rapidly after a lightning flash. The rate of change decreases as the field approaches the value it had prior to the flash. In contrast, the field a hundred metres above the ground, which is often above most of the influence of space charge produced by coronae, increases more uniformly (linearly) during the time interval between lightning flashes. This behaviour is similar to that of the field farther aloft in the interior of the cloud. Our numerical simulations of the shapes of recovery curves indicate that the corona current density is more accurately described by a cubic function than by a quadratic function of the electric field strength at the ground. Despite strong influences of coronae, three properties of the field at the ground accurately reflect what happens above the space charge layer. First, the rapid changes in electric field during a lightning flash are not usually affected by corona space charge. Second, when the field at the ground is nearly constant it usually has the same polarity as the field above the space charge layer. And third, when the field strength at the ground is nearly zero, and when certain other conditions are met, the time rate of change of the field at the ground is the same as that above the space charge layer.

Journal ArticleDOI
TL;DR: The existence of a local excitation pattern solution as well as its waveform stability is proved by the use of the Schauder fixed-point theorem and a generalized version of the Perron-Frobenius theorem of positive matrices to the function space.
Abstract: Dynamics of excitation patterns is studied in one-dimensional homogeneous lateral-inhibition type neural fields. The existence of a local excitation pattern solution as well as its waveform stability is proved by the use of the Schauder fixed-point theorem and a generalized version of the Perron-Frobenius theorem of positive matrices to the function space. The dynamics of the field is in general multi-stable so that the field can keep short-term memory.

Journal ArticleDOI
TL;DR: In this article, the authors calculate the contribution of instanton fields to the partition function of ℂℙn−1 models in two dimensions and show that forn = 2, the pure instanton gas is infrared finite, infinitely dense and generates a mass dynamically.
Abstract: We calculate exactly the contribution of instanton fields to the partition function of ℂℙn−1 models in two dimensions. Forn=2, the pure instanton gas is infrared finite, infinitely dense and generates a mass dynamically. Forn≧3, the gas corresponds to a system with complicatedn-body interactions, whose properties are yet to be explored.

Journal ArticleDOI
01 Jul 1979
TL;DR: In this paper, the authors derived expressions for the quasi-static range (the measurement distance is much less than a free-space wavelength) field components produced by infinitesimal dipole antennas located at or above that of the earth by employing finitely conducting earth theory techniques.
Abstract: Expressions for the quasi-static range (the measurement distance is much less than a free-space wavelength) field components produced by infinitesimal dipole antennas located at or above that of the earth have been derived by employing finitely conducting earth theory techniques. Formulas for the field components produced by an elevated, finite-length, horizontal electric antenna are also presented. Image theory is employed because most of the resulting integrals encountered cannot be evaluated analytically. The image theory and previously derived analytical (or in some cases, numerical integration) results are in agreement throughout the quasi-static range.

Journal ArticleDOI
TL;DR: In this paper, a theoretical study of domain walls in uniaxial displacive ferrodistortive systems is presented, where large and small-amplitude solutions corresponding to domain walls and the usual soft-mode phonons, respectively, are obtained.
Abstract: A theoretical study of domain walls in uniaxial displacive ferrodistortive systems is presented. We start from a generalized Langevin equation of motion for the movements of the ions, which includes dissipative terms and external fields, in addition to anharmonic and strain-force terms. We obtain large- and small-amplitude solutions corresponding to domain walls and the usual soft-mode phonons, respectively. We show that apart from translation the domain walls are absolutely stable solutions of our equation and that in external fields they reach a unique terminal velocity. The linear dependence of the velocity on the field allows us to define a temperature-dependent mobility which is related to the diffusion coefficient for the wall. Furthermore, we calculate analytically the dynamic structure factor due to domain walls and soft-mode phonons. We find that the Brownian motion of the domain walls leads to a very narrow Rayleigh peak. As we show in the second paper of this series, our model is useful in correlating and interpreting experiments in this field.

Journal ArticleDOI
TL;DR: In this article, it was shown that the anomalous low-temperature resistivity minima that have been observed in practically all amorphous metals can be explained by a modified Kondo mechanism as suggested by Tsuei.
Abstract: We show that the anomalous low-temperature resistivity minima that have been observed in practically all amorphous metals can be explained by a modified Kondo mechanism as suggested by Tsuei. If some spins exist in zero field, even in a ferromagnet, they will give rise to a Kondo minimum in the resistivity. We have performed a Monte Carlo calculation of the effective fields that are present at each ion in a strong ferromagnet such as ${\mathrm{Fe}}_{0.8}$ ${\mathrm{B}}_{0.2}$, using measured radial distribution functions (RDF's). Including both direct-exchange and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, we find no spins which are in zero field. However, if we include superexchange interactions between those next-nearest-neighbor magnetic atoms which are separated by a metalloid atom, there is a long tail in the distributions of fields which goes through zero and is nonzero at relatively large negative fields. This distribution can explain why the resistivity is unaltered in applied magnetic fields of up to 50 kOe. It can also explain why the resistivity minimum can shift to much higher temperatures upon the addition of a second type of magnetic element.


Journal ArticleDOI
15 Mar 1979
TL;DR: In this paper, a three-temperature kinetic theory of gaseous ion transport through neutral atomic gases, valid for electric fields of arbitrary strength without restriction on the ion mass ratio or interaction potential, is presented.
Abstract: A three-temperature kinetic theory of gaseous ion transport through neutral atomic gases, valid for electric fields of arbitrary strength without restriction on the ion—atom mass ratio or interaction potential, is presented. The theory is based on the use of a set of basis functions in which the ions are allowed to have different temperatures parallel and perpendicular to the field, neither of which is necessarily equal to the gas temperature, and for which the ion velocity distribution function is displaced from the origin. Although the theory is more difficult to use than is the two-temperature theory of Viehland and Mason and of Burnett, it has the important advantage of yielding accurate results in low orders of approximation to quantities that are intrinsically anisotropic, notably ion diffusion coefficients.