Showing papers on "Field (physics) published in 1989"
TL;DR: The superposition model was originally developed to separate the geometrical and physical information in crystal field parameters as discussed by the authors, and its success in the analysis of lanthanide spectra has paralleled by the success of the related angular overlap model in analysis of d-electron spectra.
Abstract: The superposition model was originally developed to separate the geometrical and physical information in crystal field parameters. Its success in the analysis of lanthanide spectra has been paralleled by the success of the related angular overlap model in the analysis of d-electron spectra. The basic ideas, method of application and reliability of the superposition model are discussed and its relationship with the angular overlap model is clarified. Developments described are the application of the superposition model to the ground (L=0) multiplet splittings of d5 and f7 ions, orbit-lattice interactions, transition intensities and correlation crystal fields. Special attention is paid to work which has been claimed to support or disprove the postulates of the model.
1,007 citations
TL;DR: In this article, a discrete canonical, singularity-free mapping between the five and the six degree of freedom formulation is constructed by exploiting the geometric connection between the orthogonal group (SO(3)) and the unit sphere (S2).
Abstract: Computational aspects of a linear stress resultant (classical) shell theory, obtained by systematic linearization of the geometrically exact nonlinear theory, considered in Part I of this work, are examined in detail. In particular, finite element interpolations for the reference director field and the linearized rotation field are constructed such that the underlying geometric structure of the continuum theory is preserved exactly by the discrete approximation. A discrete canonical, singularity-free mapping between the five and the six degree of freedom formulation is constructed by exploiting the geometric connection between the orthogonal group (SO(3)) and the unit sphere (S2). The proposed numerical treatment of the membrane and bending fields, based on a mixed Hellinger-Reissner formulation,provides excellent results for the 4-node bilinear isoparametric element. As an example, convergent results are obtained for rather coarse meshes in fairly demanding, singularity-dominated, problems such as the classical rhombic plate test. The proposed theory and finite element implementation are evaluated through an extensive set of benchmark problems. The results obtained with the present approach exactly match previous solutions obtained with state-of-the-art implementations based on the so-called degenerated solid approach.
450 citations
TL;DR: In this article, it is suggested that the polar heliospheric magnetic field at large heliocentric distances may deviate considerably from the generally accepted Archimedean spiral, and that the large-scale field near the poles may be dominated by randomly oriented transverse magnetic fields with magnitude much larger than the average spiral.
Abstract: It is suggested that the polar heliospheric magnetic field, at large heliocentric distances, may deviate considerably from the generally accepted Archimedean spiral. Instead, it is suggested that the large-scale field near the poles may be dominated by randomly-oriented transverse magnetic fields with magnitude much larger than the average spiral. The average vector field is still the spiral, but the average magnitude may be much larger. In addition, the field direction is transverse to the radial direction most of the time instead of being nearly radial. This magnetic-field structure has important consequences for the transport of cosmic rays. Preliminary model calculations suggest changes in the radial gradient of galactic cosmic rays which may improve agreement with observations.
356 citations
TL;DR: In this paper, the McCutchen theorem is used to derive the necessary conditions for a nondiffracting field to propagate in free space with their energy confined around their axis but that experience no spread or divergence.
Abstract: Recently Durnin pointed out the existence of nondiffracting beams that propagate in free space with their energy confined around their axis but that experience no spread or divergence [ J. Opt. Soc. Am. A4, 651 ( 1987)]. This Communication provides an alternative way of interpreting these results. The approach is based on the McCutchen theorem from which the necessary conditions for a nondiffracting field are derived. This description may be useful in suggesting several different means of synthesizing such fields and in providing a convenient way of estimating their practical limitations. Some examples, inspired by known techniques studied for depth of field enhancement, are briefly mentioned.
291 citations
TL;DR: A scaling relationship between switching fields, of which remanent coercivity is a prominent example, and measurement time is derived, and the energy barrier to thermal fluctuations is found to exhibit a 3/2-power dependence on the difference between the applied field and the nonthermally assisted switching field.
Abstract: A scaling relationship between switching fields, of which remanent coercivity is a prominent example, and measurement time is derived. The energy barrier to thermal fluctuations is found to exhibit a (3/2-power dependence on the difference between the applied field and the nonthermally assisted switching field. This (3/2-power dependence contrasts with the 2-power dependence which has been widely assumed in the literature. Implications for magnetic viscosity and the orientational dependence of the time-dependent switching field in certain small, isolated particles are also discussed.
284 citations
TL;DR: The analysis is shown to correctly predict the low-field amplitudes and phases of the de Haas\char21{}Shubnikov oscillation in both the longitudinal and Hall resistivities of two samples.
Abstract: We have analyzed the current theories of the conductivity of a two-dimensional electron gas in low magnetic fields to determine the correct usage of the transport and quantum lifetimes. The analysis is shown to correctly predict the low-field amplitudes and phases of the de Haas\char21{}Shubnikov oscillation in both the longitudinal and Hall resistivities of two samples. Deviations at high fields are attributed to localization.
258 citations
TL;DR: In this article, the holonomy along lines parallel to the time-axis is computed for one-and two-baryon physics, which are good approximations to the SKYME field configurations.
226 citations
TL;DR: In this paper, a method for representing surfaces as solutions to partial differential equations is proposed, which can easily achieve the required degree of continuity between the blend and the surfaces to which it attaches.
Abstract: A method is proposed for representing surfaces as solutions to partial differential equations. It is shown, by examples from the field of blend generation, that the method can easily achieve the required degree of continuity between the blend and the surfaces to which it attaches. The surfaces also have the property of being geometrically ‘well-behaved’.
223 citations
219 citations
TL;DR: This work proposes a macroscopic critical-state model as an alternative to the loop model used by Jeffries et al. and finds that, as the magnetic field is increased, the critical current crosses over from the Bean regime, where ${J}_{c}$ is independent of field, to the Anderson-Kim regime, which is approximately inversely proportional to the field.
Abstract: High-temperature superconductors exhibit harmonic generation when immersed in an ac magnetic field. To explain this phenomenon, we propose a macroscopic critical-state model as an alternative to the loop model used by Jeffries et al. While the original Bean model of the critical state only predicts odd harmonics, our extended model also predicts even harmonics by taking into account the dependence of the critical current upon magnetic field. The results of our measurements of harmonic signals as a function of ac magnetic field, dc magnetic field, temperature, and harmonic number are consistent with the proposed model. In particular, we find that, as the magnetic field is increased, the critical current crosses over from the Bean regime, where ${J}_{c}$ is independent of field, to the Anderson-Kim regime, where ${J}_{c}$ is approximately inversely proportional to the field.
214 citations
TL;DR: In this paper, the authors presented results of direct numerical simulations of stably stratified, freely evolving, homogeneous turbulence, and showed that the results have a satisfactory degree of realism, insofar as statistical parameters such as total energy and length scales are concerned.
Abstract: Results of direct numerical simulations of stably stratified, freely evolving, homogeneous turbulence are presented. An examination of initial data designed to give insight into laboratory flows suggests that the numerical simulations have a satisfactory degree of realism, insofar as statistical parameters such as total energy and length scales are concerned. The motion is decomposed into a stratified turbulence (vortical) component and a wave component. For initial-value problems similar to laboratory studies of stratified flows, the vortical component decays at a rate virtually identical to that of the non-buoyant case up to t = 6N−1 (N is the Brunt-Vaisala frequency). The decay rate decreases after this time, suggesting a kind of turbulence ‘collapse’. The temperature structure that emerges clearly shows the development of the collapse stage of the flow, which is also diagnosed by the behaviour of parameters such as the Thorpe scale.We next examine the very small-Froude-number regime in order to understand possible universal aspects of the flow. An examination of various initial conditions with different proportions of stratified and wave components indicates a lack of universality. For initial data containing only vortical motion (motions derived from the vertical vorticity field), the vortical field tends to dominate, in subsequent evolution, at strong stratification. However, contrary to two-dimensional turbulence, the flow is more strongly dissipative than two-dimensional flows due to the frictional effect associated with layering. Other quantities examined are frequency spectra, and the probability distribution for vertical shear. The frequency spectra exhibit some features in common with spectra extracted from oceanographic data.
TL;DR: In this article, the fundamental ideas of the recently opened field of two-particle interferometry, which employs spatially separated, quantum mechanically entangled twoparticle states, are discussed.
Abstract: An exposition is given of the fundamental ideas of the recently opened field of two-particle interferometry, which employs spatially separated, quantum mechanically entangled two-particle states. These ideas are illustrated by a realizable arrangement, in which four beams are selected from the output of a laser-pumped down-converting crystal, with two beams interferometrically combined at one locus and two at another. When phase shifters are placed in these beams, the coincident count rates at the two loci will oscillate as the phases are varied, but the single count rates will not.
TL;DR: In this article, a series of very long molecular dynamics simulations has been completed for the rigid simple point charge (SPC) and transferrable intermolecular potential 4P (TIP4P) water models with reaction field boundary conditions.
Abstract: A series of very long molecular dynamics simulations has been completed for the rigid simple point charge (SPC) and transferrable intermolecular potential 4P (TIP4P) water models with reaction field boundary conditions. The dielectric constant corresponding to these models was evaluated in two ways: (1) by calculating the fluctuations in the mean square dipole moment of the system in the absence of an applied field and (2) by evaluating the polarization response of the system to an applied field. Consistent values for the dielectric constant are obtained by the two methods. For the TIP4P water model, the dielectric constant e0 is calculated to be ∼50 at 293 K, in agreement with previously published results. For the rigid SPC model, e0 is calculated to be ∼68 at 300 K and ∼59 at 350 K. The calculated dielectric constant is shown to be very sensitive to the way in which the truncation of long‐range forces is treated, although the short‐range liquid properties are insensitive to the truncation procedure. The effects on the dielectric response of system size, cutoff radius, and the smoothing of long range interactions at the cutoff boundary are examined. It is found that the introduction of a smoothing function causes perturbations of the water–water angular orientation correlation functions which can result in large errors in the calculated dielectric constant.
TL;DR: In this paper, the authors developed the quantization of topological solitons (vortices) in three-dimensional quantum field theory, in terms of the Euclidean region functional integral.
Abstract: We develop the quantization of topological solitons (vortices) in three-dimensional quantum field theory, in terms of the Euclidean region functional integral. We analyze in some detail the vortices of the abelian Higgs model. If a Chern-Simons term is added to the action, the vortices turn out to be “anyons,” i.e. particles with arbitrary real spin and intermediate (Θ) statistics. Localization properties of the interpolating field, scattering theory and spin-statistics connection of anyons are discussed. Such analysis might be relevant in connection with the fractional quantum Hall effect and two-dimensional models of HighTcsuperconductors.
TL;DR: In this article, the authors proposed a simple model in which the corona is represented by the half-space domain and the photosphere by the boundary plane ∂Ω = {z = 0}.
Abstract: Using a simple model in which the corona is represented by the half-space domain Ω = {z > 0} and the photosphere by the boundary plane ∂Ω = {z = 0}, we discuss some important aspects of the general problem of the reconstruction of the magnetic field B in a small isolated coronal region from the values of the vector B¦
∂Ω
measured by a magnetograph over its whole basis. Assuming B to be force-free in Ω: (i) we derive a series of relations which must be necessarily satisfied by the boundary field B¦
∂Ω
, and then by the magnetograph data if the force-free assumption is actually correct; (ii) we show how to extract directly from the measured B¦
∂Ω
some useful informations about the energy of B in Ω and the topological structure of its field lines; (iii) we present a critical discussion of the two methods which have been proposed so far for computing effectively B in Ω from B¦
∂Ω
.
TL;DR: In this paper, the authors compare two models of vadose zone solute transport: the deterministic one-dimensional convection dispersion model and the stochastic-convective lognormal transfer function model.
Abstract: The solute concentrations measured in the field experiment of G. L. Butters et al. (this issue) are used to compare two models of vadose zone solute transport: the deterministic one-dimensional convection-dispersion model, which represents solute transport far from the source of solute entry, and the stochastic-convective lognormal transfer function model, which represents solute transport near the source. The stochastic-convective model provided an excellent representation of the spreading of the solute pulse to a depth of 3 m after calibration at 0.3 m. Conversely, the deterministic model dramatically underpredicted solute spreading beyond 0.3 m after calibration. An analysis of the area-averaged solute concentration revealed a nearly linear scale effect in the dispersivity to a depth of at least 14.8 m. A change in the growth pattern of dispersion observed in the breakthrough curve at 4.5 m was attributed to a soil texture change near 3 m, which caused the apparent dispersivity of the pulse to decrease between 3.0 and 4.5 m, after which it increased significantly between 4.5 m and the final profile sampling between 0 and 25 m.
TL;DR: In this paper, the authors discuss the limitations and usefulness of linear force-free magnetic field formulations, specific phenomenological and topological parameters of these formulations, and their usefulness, and the relationship of the integral and Fourier procedures is shown explicitly.
Abstract: This paper discusses the interconnection of the various linear force-free magnetic field formulations, the specific phenomenological and topological parameters of these formulations, and their usefulness. Particularly, the limitations and usefulness of linear force-free fields are discussed. Specific field configurations are related to magnetographic interpretation. The relationship of the integral and Fourier procedures is shown explicitly. The physical interpretation of linear force-free fields is shown by analytic models and from the Marshall Space Flight Center solar vector magnetograms.
TL;DR: In this paper, it was shown that the topological solutions of the Maxwell equations in vacuum have a Hopf index equal to the linking number of any pair of magnetic lines, which allows the classification of the electromagnetic fields into homotopy classes, labeled by the value of the helicity.
Abstract: It is shown that Maxwell equations in vacuum derive from an underlying topological structure given by a scalar field ϕ which represents a map S3×R→S2 and determines the electromagnetic field through a certain transformation, which also linearizes the highly nonlinear field equations to the Maxwell equations. As a consequence, Maxwell equations in vacuum have topological solutions, characterized by a Hopf index equal to the linking number of any pair of magnetic lines. This allows the classification of the electromagnetic fields into homotopy classes, labeled by the value of the helicity. Although the model makes use of only c-number fields, the helicity always verifies ∫ A·Bd3r=nα, n being an integer and α an action constant, which necessarily appears in the theory, because of reasons of dimensionality.
TL;DR: In this paper, the authors present a review of techniques for computational modeling of magnetic fields in solar active regions, including current-free, constant-α and general force-free fields.
Abstract: The magnetic field plays an important role in various solar activities. This paper reviews techniques for computational modeling of magnetic fields in solar active regions. The input data are photospheric magnetic fields supplied by magnetograph observations. The field above the photosphere is computed by assuming an equation for the magnetic field. Three classes of magnetic fields, namely current-free fields, constant-α force-free fields, and general force-free fields are considered. Their physical/mathematical significances and computational procedures are systematically presented.
TL;DR: In this article, a theory for the motion of a charged ellipsoidal particle in a uniform electric field is developed for the translation and rotation of the particle, where the velocity depends on the monopole and quadrupole moments of the zeta potential as well as on the orientation of a particle with respect to the applied electric field, while the angular velocity is proportional to the crossproduct between the dipole moment and the field.
TL;DR: In this article, the cosmological constant measured experimentally is not in general given by the coefficient of √−g in some effective action but rather by the coefficients of gμν in the effective Einstein equations.
TL;DR: In this paper, a time-domain technique is presented for computing the internal electromagnetic field within a one-dimensional medium characterized by spatially varying conductivity and permittivity profiles.
TL;DR: In this article, a new formulation for off-axis focal points is introduced that has the desirable properties of increased accuracy for larger field angles, invariance to shifts of the focal point about spheres of constant radius when the detection point is on the sphere for both intensity and amplitude fields, and invariance for shifts in three transformed coordinates for intensity fields.
Abstract: Existing formulations of the three-dimensional (3-D) diffraction pattern of spherical waves that is produced by a circular aperture are reviewed in the context of 3-D serial-sectioning microscopy. A new formulation for off-axis focal points is introduced that has the desirable properties of increased accuracy for larger field angles, invariance to shifts of the focal point about spheres of constant radius when the detection point is on the sphere for both intensity and amplitude fields, and invariance to shifts in three transformed coordinates for intensity fields. Finally, calculated intensity fields for both on-axis and off-axis focal points are included to illustrate the proposal that the classical 3-D diffraction patterns that have been used as analytical models in 3-D serial-sectioning fluorescence microscopy may not be accurate enough for this application.
TL;DR: This comment on the article by Matsumoto and Kataoka identifies a discrepancy between recent calculations of the surface potential of the water liquid–vapor interface that is associated with the densities of molecular quadrupole moment in the coexisting bulk phases.
Abstract: This comment on the article by Matsumoto and Kataoka [J. Chem. Phys. 88, 3233 (1988)] identifies a discrepancy between recent calculations of the surface potential of the water liquid–vapor interface. The cited work assumes that the field of a water molecule in the interfacial region is strictly the field of a point molecular dipole, whereas other works have made more detailed assumptions about the molecular charge distributions. The difference between the values for the surface potential obtained from these different assumptions is large compared to the surface potential value in question. It is shown that the numerical difference is associated with the densities of molecular quadrupole moment in the coexisting bulk phases. The correction can be evaluated analytically and applied to the molecular dynamics results after the fact.
TL;DR: In this article, the effect of external fields on the structural and electronic properties of Ag(110) was investigated using local density-functional theory, and the surface interlayer spacings were found to be insensitive to the applied field in the absence of field-induced surface reconstruction.
Abstract: The effect of external fields on the structural and electronic properties of Ag(110) is investigated using local-density-functional theory. We find that Ag(110) undergoes a (1×2) missing-row reconstruction as an excess charge of ≃0.05 electron per surface atom is added onto the surface. Our result supports an electron-donation mechanism for the alkali-metals-induced reconstruction on the (110) surface of the 3d and 4d fcc metals. The surface interlayer spacings are found to be insensitive to the applied field in the absence of field-induced surface reconstruction
TL;DR: In this article, it was shown that the motion of a two-level atom through a spatially varying single-mode field gives rise to nonlinear transient effects which are similar to self-induced transparency and adiabatic following.
TL;DR: A quantum theory of the propagation of a single-mode resonant field through a Kerr-like medium is given and the existence of the quantum collapses and revivals in the otherwise periodic exchange of energy between the field and the atomic oscillator is shown.
Abstract: A quantum theory of the propagation of a single-mode resonant field through a Kerr-like medium is given. Numerical studies show the existence of the quantum collapses and revivals in the otherwise periodic exchange of energy between the field and the atomic oscillator. Approximate analytical methods are developed to explain the numerical results for the case of weak nonlinearity of the Kerr medium. For large nonlinearity, the correspondence with the Jaynes-Cummings model is discussed.
TL;DR: In this article, the results of fully compressible, Fourier collocation, numerical simulations of the Orszag-Tang vortex system are presented, and it is found that compressible effects develop within one or two Alfven transit times, as manifested in the spectra of compressible quantities such as the mass density and the nonsolenoidal flow field.
Abstract: In this paper the results of fully compressible, Fourier collocation, numerical simulations of the Orszag–Tang vortex system are presented. The initial conditions for this system consist of a nonrandom, periodic field in which the magnetic and velocity field contain X points but differ in modal structure along one spatial direction. The velocity field is initially solenoidal, with the total initial pressure field consisting of the superposition of the appropriate incompressible pressure distribution upon a flat pressure field corresponding to the initial, average Mach number of the flow. In these numerical simulations, this initial Mach number is varied from 0.2–0.6. These values correspond to average plasma beta values ranging from 30.0 to 3.3, respectively. It is found that compressible effects develop within one or two Alfven transit times, as manifested in the spectra of compressible quantities such as the mass density and the nonsolenoidal flow field. These effects include (1) a retardation of growth of correlation between the magnetic field and the velocity field, (2) the emergence of compressible small‐scale structure such as massive jets, and (3) bifurcation of eddies in the compressible flow field. Differences between the incompressible and compressible results tend to increase with increasing initial average Mach number.
TL;DR: On met en evidence des ecarts par rapport a la loi d'Einstein lorsque le desordre et le champ augmentent, que l'on attribue a un phenomene de diffusion anormal induit par le champ alors that the mobilite reste constante.
Abstract: Employing Monte Carlo techniques, the diffusion and drift of charge carriers within an array of hopping states subject to a Gaussian distribution of site energies of width \ensuremath{\sigma} has been studied as a function of \ensuremath{\sigma}/kT and electric field. With increasing disorder and field, significant deviations from Einstein's law are noted. They are shown to be the consequence of anomalous, field-assisted diffusion while the mobility remains constant. The effect can account for anomalous transit-time dispersion observed in polymeric photoconductors exhibiting time independent transport.
Book•
01 Jan 1989
TL;DR: This introduction to the major techniques of surface analysis, written by specialists in the field with practical experience, includes the ways in which these techniques can be used to solve problems on surfaces, interfaces, thin films and surface coatings.
Abstract: This introduction to the major techniques of surface analysis, written by specialists in the field with practical experience, includes the ways in which these techniques can be used to solve problems on surfaces, interfaces, thin films and surface coatings.