Showing papers on "Field (physics) published in 1971"
TL;DR: In this paper, the non-linear optical polarization of an isolated atom or molecule is treated, giving careful consideration to secular and resonant terms in the perturbation expansion, and the Method of Averages introduced by Bogoliubov and Mitropolsky is used.
Abstract: The non-linear optical polarization of an isolated atom or molecule is treated, giving careful consideration to secular and resonant terms in the perturbation expansion. The Method of Averages introduced by Bogoliubov and Mitropolsky is used. The case where resonance-induced excited state populations are negligible, which is relevant to a wide range of non-linear optical experiments, is examined in detail for polarizations through third order in the perturbing fields. This yields concise expressions which are valid for any combination of applied field frequencies, including static fields.
1,184 citations
TL;DR: Topside ionospheric instabilities of electrostatic ion acoustic and ion cyclotron waves to field aligned currents in single and multiion plasmas are discussed in this paper.
Abstract: Topside ionospheric instabilities of electrostatic ion acoustic and ion cyclotron waves to field aligned currents in single and multiion plasmas
872 citations
TL;DR: In this paper, it was shown that the exact Lorentz-Dirac equation of motion for a strictly point charge is nothing more than the usual LDA when the retarded self-field of the particle is properly taken into account, as required for the very consistency of the idea of energymomentum localization in the field.
Abstract: It is shown that the exact Lorentz-Dirac equation of motion for a strictly point charge is nothing more than the usual Lorentz force law when the retarded self-field of the particle is properly taken into account, as required for the very consistency of the idea of energy-momentum localization in the field.
732 citations
TL;DR: For the massless Yang-Mills field, a generalized Ward-Takahashi identity was derived in this paper, which implies that Z 1 / Z 2 has a common value for the vector field and for the "fictious" scalar field.
706 citations
TL;DR: In this article, it was shown that overlap and covalency make the dominant contributions to the observed field, the electrostatic contributions only being inportant for the potential components with low angular dependence (i.e., the n=2 parameters).
Abstract: Recent progress in understanding the origin of the lanthanide crystal field is summarized. The basic assumption of the crystal field parametrization is shown to be that the crystalline environment can be represented as a one-electron potential, and the consequences of removing this assumption are traced. It is further shown that overlap and covalency make the dominant contributions to the observed field, the electrostatic contributions only being inportant for the potential components with low angular dependence (i.e. the n=2 parameters). In some circumstances it is found that the observed parameters can usefully be analysed into superposed contributions from the neighbouring ions in the crystal. The importance of crystal field concepts in related problems is emphasized as well as the stimulus crystal field theory gives to the development of formalisms for dealing with non-orthogonal basis states.
568 citations
TL;DR: In this paper, a simple test to distinguish multidomain and single-domain carriers of remanence is designed that makes use of the distinctive demagnetization characteristics.
Abstract: It is demonstrated that the stability against af demagnetization of TRM carried by multidomain magnetite increases with increasing strength of the inducing field. This multidomain field-dependence trend of stability against af demagnetization is opposite to that of single-domain particles. A simple test to distinguish multidomain and single-domain carriers of remanence is designed that makes use of the distinctive af demagnetization characteristics. The test was applied to a variety of igneous rocks. None of these showed truly multidomain characteristics. Thus, although some TRM is undoubtedly multidomain in these rocks, the TRM is dominated by single-domain carriers. These results are consistent with the growing evidence of the importance of very fine grained magnetite as a carrier of NRM in many igneous rocks.
366 citations
TL;DR: In this article, the adiabatic theory for charged particles moving in a region where the main component of the magnetic field reverses its direction is presented for charge-reconnection geometry.
Abstract: The adiabatic theory is presented for charged particles moving in a region where the main component of the magnetic field reverses its direction. The unperturbed field configuration is one-dimensional and involves two regions of uniform and opposite magnetic fields separated by a reversal region of small but finite extent. The adiabatic theory is capable of describing particle orbits when gradual spatial and/or temporal field variations are added to this configuration. Several applications are given. These include orbits during a null-sheet compression, orbits in the sheets studied by Alfven and Speiser, and orbits in the vicinity of the magnetic null line of the so-called field-reconnection geometry.
302 citations
TL;DR: In this article, a local Lagrangian density, depending on a pair of four-potentials and charged fields with electric and magnetic charges, is presented, which is equivalent to the Dirac's and Maxwell's equations.
Abstract: We present a local Lagrangian density, depending on a pair of four-potentials $A$ and $B$, and charged fields ${\ensuremath{\psi}}_{n}$ with electric and magnetic charges ${e}_{n}$ and ${g}_{n}$. The resulting local Lagrangian field equations are equivalent to Maxwell's and Dirac's equations. The Lagrangian depends on a fixed four-vector, so manifest isotropy is lost and is regained only for quantized values of (${e}_{n}{g}_{m}\ensuremath{-}{g}_{n}{e}_{m}$). This condition results from the requirement that the representation of the Poincar\'e Lie algebra which results from Poincar\'e invariance, integrate to a representation of the finite Poincar\'e group. The finite Lorentz transformation laws of $A$, $B$, and ${\ensuremath{\psi}}_{n}$ are presented here for the first time. The familiar apparatus of Lagrangian field theory is applied to yield directly the canonical commutation relations, the energy-momentum tensor, and Feynman's rules.
269 citations
TL;DR: In this article, a simple procedure for obtaining the distributions of magnetic hyperfine fields from Mossbauer spectra is outlined, based on which a simple algorithm is proposed to obtain the distribution of hyperfine magnetic fields from the spectra.
Abstract: A simple procedure for obtaining the distributions of magnetic hyperfine fields from Mossbauer spectra is outlined.
258 citations
TL;DR: In this paper, it was shown that the metric coefficients of such space-times depend essentially on the single variablez=r/t wherer is a radial coordinate andt is the time.
Abstract: Spherically symmetric space-times which admit a one parameter group of conformal transformations generated by a vectorξ
μ
such thatξ
μ;v
+ξ
v;μ
=2g
μv
are studied. It is shown that the metric coefficients of such space-times depend essentially on the single variablez=r/t wherer is a radial coordinate andt is the time. The Einstein field equations then reduce to ordinary differential equations. The solutions of these equations are analogous to the similarity solutions of the classical theory of hydrodynamics. In case the source of the field is a perfect fluid whose specific internal energy is a function of temperature alone, the solution of the field equations is uniquely determined by specifying data on the time-like hypersurfacez=constant and is a similarity solution. The problem of fitting a similarity solution to another solution of the field equations across a shock described by the hypersurfacez=constant is treated. A particular similarity solution for whichw=3p obtains is shown to describe a Robertson-Walker space-time. This solution is fitted to a special static solution of the Einstein field equations which has a singularity atr=0. The resulting solution of the Einstein field equations is shown to be regular everywhere except atr=0≧t and the shock. The special Robertson-Walker metric is also fitted to a particular class of collapsing dust solutions (which are also similarity solutions) across a shock. The resulting solution is regular everywhere except atr=t=0 and on the shock.
237 citations
TL;DR: Galactic magnetic field generation by dynamo process with nonuniform rotation and turbulence in gaseous disk was described in this article, where the authors proposed a dynamo-based approach to generate magnetic field.
Abstract: Galactic magnetic field generation by dynamo process with nonuniform rotation and turbulence in gaseous disk
TL;DR: In this article, an extension of the Helfrich theory of hydrodynamic instabilities to the case of alternating electric fields is presented, where the electrohydrodynamic effects are described by two coupled equations for the charge density (q) and the local curvature of the molecular alignment (ψ).
Abstract: We present an extension of the Helfrich theory of hydrodynamic instabilities to the case of alternating electric fields. The electrohydrodynamic effects are described by two coupled equations for the charge density (q) and the local curvature of the molecular alignment (ψ). The relaxation time for q is the dielectric relaxation time τ (∼ 10-2 s in typical samples). The relaxation time T for ψ is strongly dependent on the field magnitude. Provided that the sample thickness d is above a certain limit dc, the nature of the instability is very different, depending on the ratio of the field frequency ω to a critical frequency ω c. For ω ωc the situation at threshold corresponds to a constant q and an oscillating ψ. These predictions, together with the calculated curves of threshold voltage vs ω and d, are in reasonable agreement with a number of recent experiments.
TL;DR: In this article, the use of rays to construct fields is illustrated by finding the field in the region z>0 when the field is given on the plane z = 0, where the calculation involves only complex rays.
Abstract: The use of rays to construct fields is illustrated by finding the field in the region z>0 when the field is given on the plane z = 0. This construction is valid for complex rays as well as real ones. The method is applied to a gaussian field in the plane z = 0, in which case a gaussian beam results. The calculation involves only complex rays. Exactly the same results are also obtained by applying the method of stationary phase to an integral representation of the field. However, the ray method is simpler than the stationary-phase method, and it is also applicable to problems for which the stationary-phase method cannot be used because no integral representation of the field is known.
Journal Article•
TL;DR: In this paper, the authors compare the Flyter PHENOMENA of the SUSPENSION BRIDGE to the AIRFOIL and test out the NATURE of AERODYNAMIC OSCILLATORY FORCES under an exponerent MOTION.
Abstract: THE FLUTTER PHENOMENA OF THE SUSPENSION BRIDGE IS COMPARED TO THE AIRFOIL. A FREE-OSCILLATION EXPERIMENTAL METHOD IS USED TO MEASURE MODEL BRIDGE FLUTTER COEFFICIENTS ANALOGOUS TO AIRFOIL FLUTTER COEFFICIENTS. THE AIRFOIL IS EMPLOYED AS A CHECK ON THE EXPERIMENTAL METHOD, BOTH AS A THEORETICAL BAKCDROP AND TO TEST OUT THE NATURE OF AERODYNAMIC OSCILLATORY FORCES UNDER EXPONENTIALLY MODIFIED MOTION. A SHORT CATALOGUE OF BRIDGE DECK FLUTTER COEFFICIENTS WAS EXPERIMENTALLY OBTAINED AND COVERS A RANGE OF BRIDGE DECK FORMS. DETAILED RESULTS ARE DESCRIBED TO ACCOUNT FOR A NUMBER OF PHENOMENA OBSERVED IN THE WIND TUNNEL AND IN THE FIELD. /AUTHOR/
TL;DR: In this paper, a system of experiments based on microwave induced signals is presented which enables one to solve the dynamics of populating and depopulating the individual levels of the phosphorescent state.
Abstract: It is known that at low temperatures relaxation between the spin components of a phosphorescent triplet state of an organic molecule may become very slow as compared to their individual rates of decay. Spectacular changes in the intensity emitted can then be induced by suddenly sweeping a microwave field through one of the zero-field resonances during phosphorescence decay. These microwave induced signals arise because molecules are transferred from a populated non-radiative level to an empty radiative one. In this paper a system of experiments based on this phenomenon is presented which enables one to solve the dynamics of populating and depopulating the individual levels of the phosphorescent state. As a demonstration results of experiments on the aza-naphthalenes quinoline and quinoxaline are given.
TL;DR: A wide class of exact solutions of the stationary Einstein-Maxwell equations characterized by a flat "background" three-space is obtained in this article, where the solutions can be interpreted as the external gravitational and electromagnetic fields of one or more spinning sources with unit specific charge in stationary configuration.
Abstract: A wide class of exact solutions of the stationary Einstein-Maxwell equations characterized by a flat "background" three-space is obtained. The solutions can be interpreted as the external gravitational and electromagnetic fields of one or more spinning sources with unit specific charge in stationary configuration.
TL;DR: In this article, the threshold ac electric field required for the excitation of the purely growing "oscillating two-stream" and decay instabilities is found to increase when the density gradient scale length H becomes less than the mean free path.
Abstract: The threshold ac electric field required for the excitation of the purely growing “oscillating two‐stream” and decay instabilities is found to increase when the density‐gradient scale length H becomes less than the mean free path. For a plasma with no magnetic field, the threshold field is given by E2/4πnTe≈2(k‖H)−1, where k‖≲(1/4)D−1 is the wavenumber of the instability in the direction orthogonal to the density gradient. (D is the electron Debye length.) Qualitative arguments suggest that this result should hold in the presence of a magnetic field. Recent experimental measurements of the threshold field agree well with these theoretical calculations. The reason for the threshold field increasing is that, in an inhomogeneous plasma, the unstable region has a finite extent spatially and energy (in the form of electron plasma waves) can propagate out of this region, thus creating an energy loss not found in uniform plasmas.
TL;DR: In this paper, the authors developed a theoretical solution for the electromagnetic response of a two-dimensional inhomogeneity in a conductive half-space, in the field of a line source of current.
Abstract: A theoretical solution is developed for the electromagnetic response of a two‐dimensional inhomogeneity in a conductive half‐space, in the field of a line source of current. The solution is in the form of an integral equation, which is reduced to a matrix equation, and solved numerically for the electric field in the body. The electric and magnetic fields at the surface of the half‐space are found by integrating the half‐space Green’s functions over the scattering currents. One advantage of this particular numerical technique is that it is necessary to solve for scattering currents only in the conductor and not throughout the half‐space. The response of a thin, vertical conductor is studied in some detail. Because the only interpretational aids available previously were scale model results for conductors in free space, the results presented here should be useful in interpreting data and in designing new EM systems. As expected, anomalies decay rapidly as depth of burial is increased, due to attenuation in...
TL;DR: In this paper, it was shown that dc, ac, or hf electric field acts across a vertical tube filled with a mixture of natural gas (CH4) or ethylene and air at 1 atm, the speed of flame propagation is shown to rise well above its value in zero field; however, no effect is found in town gas-air mixtures.
TL;DR: In this article, the authors propose a method of small and large scale perturbation by large-scale inhomogeneities, based on the distribution laws of the fluctuations in the scattered field.
Abstract: 1. Introduction 3 2. Method of Small Perturbations. First Approximation 6 3. Scattering by Large-scale Inhomogeneities 8 a. Method of Smooth Perturbations 10 b . Parabolic-equation Method 14 c . Markov Approximation 16 d. Distribution Laws of the Fluctuations in the Scattered field 22 4. Theory of Multiple Scattering 23 Bibliography 32
TL;DR: In this article, it was shown that in all solutions of the Einstein-Boltzmann equations in which the particle distribution function is isotropic about some 4-velocity field, the distortion of that velocity field vanishes; further, either its expansion or its rotation vanishes.
Abstract: It is shown that in all solutions of the Einstein-Boltzmann equations in which the particle distribution function is isotropic about some 4-velocity field, the distortion of that velocity field vanishes; further, either its expansion or its rotation vanishes. We discuss briefly further kinetic solutions in which the energy-momentum tensor has a perfect fluid form.
TL;DR: In this paper, the effect of strong magnetic fields on neutron stars or white dwarfs is calculated for Thomson scattering in a fully ionized collisionless plasma, and the photon mean free path can be greatly extended for propagation nearly parallel or, for the extraordinary mode, nearly perpendicular to the field.
Abstract: The effect of a strong magnetic field on neutron stars or white dwarfs is calculated for Thomson scattering in a fully ionized collisionless plasma. The photon mean free path can be greatly extended for propagation nearly parallel or, for the extraordinary mode, nearly perpendicular to the field.
TL;DR: In this paper, it was shown that given a curved space-time with a metric tensorgij, Maxwell's equations may be written as if they were valid in a flat space time in which there is an optical medium with a constitutive equation.
Abstract: Given a curved space-time with a metric tensorgij, Maxwell's equations may be written as if they were valid in a flat space-time in which there is an optical medium with a constitutive equation.
TL;DR: The VLF-E.M. (Very Low Frequency-Electro Magnetics) method was first used for geophysical surveying in 1964 as mentioned in this paper, and many hundreds of surveys have been carried out; several variations on the original design have been introduced; and the method has become airborne.
01 Feb 1971
TL;DR: In this article, it was shown that the α + FeAl two-phase field closes at around 662 C where both phases have the same composition: 23.9 at. pct Al and 18.75 to 32 at.pct Al.
Abstract: X-ray diffraction study of isothermally annealed powder specimens of Fe-Al alloys with 18.75 to 32 at. pct Al indicates that the α + FeAl two-phase field closes at around 662‡C where both phases have the same composition: 23.9 at. pct Al. X-ray diffraction and magnetic data show that any twophase field that may exist between the FeAl and Fe3Al phases must be extremely narrow. It is probable that there is no two-phase field and that the transition is of a higher than first order type.
TL;DR: In this paper, a pump frequency near 3 GHz is used to parametrically amplify the sound wave at one half the pump frequency and this process forms a method of generating sound waves throughout the crystal volume.
Abstract: The parametric interaction between two oppositely traveling sound waves and a nonspatially varying (k = 0) rf electric field in lithium niobate is illustrated in this paper. A pump frequency near 3 GHz is used to parametrically amplify the sound wave at one‐half the pump frequency. In addition with a pump field that is sufficiently strong parametric oscillations occur within the crystal and this process forms a method of generating sound waves throughout the crystal volume. Finally, we have found that this type of parametric mixing of two sound waves can be used to obtain convolution signals in real time by monitoring the electric polarization generated within the crystal at twice the signal frequency.
TL;DR: In this paper, the first appearance of reliable results for the scattered field from two spheres of radii larger than one wavelength and as large as ten or more was presented. But these results were only applied to three collinear spheres of various materials.
Abstract: In [8], both low- and high-frequency solutions to the two-sphere problem were presented in a form suitable for efficient computer solution, Here, numerical results are presented using a method which has enabled the first appearance of reliable results for the scattered field from two spheres of radii larger than one wavelength and as large as ten or more. Radar cross sections (RCS) are computed for numerous configurations of two spheres of various materials. Results for scattering by three collinear spheres are also given. An experimental program was undertaken and is briefly described. Whenever possible, these results are compared with the theory. In all cases the agreement is excellent. Depolarization due to multiple scattering is also investigated, revealing some interesting effects and practical applications to scattering range calibration.