Showing papers on "Field (physics) published in 1980"

Effect of an intense electromagnetic field on a weakly bound system

Abstract: The approximation method introduced by Keldysh is revised and extended. The technique is applicable to the photodetachment by a plane-wave field of an electron bound by a short-range potential. The approximation is to neglect the effect of the binding potential as compared to the field effects on the final state of the detached electron. By choice of a different gauge than that used by Keldysh, the formalism becomes very simple and tractable. A general basis for the formalism is developed, and it is then applied to find transition probabilities for any order of interaction for both linearly and circularly polarized plane-wave fields. The low-intensity, first-order limit and the high-intensity, high-order limit yield the correct results. Two intensity parameters are identified. The fundamental one is $z=\frac{{e}^{2}{a}^{2}}{4m\ensuremath{\omega}}$, where $a$ is the magnitude of the vector potential (in radiation gauge) of the field of circular frequency $\ensuremath{\omega}$. The second parameter is ${z}_{1}=\frac{2z\ensuremath{\omega}}{{E}_{B}}$, where ${E}_{B}$ is binding energy, and it becomes important only in the asymptotic case. With the assumption that the field leaves the neutral atomic core relatively unaffected, the formalism is applied to the example of the negative hydrogen ion irradiated by circularly or linearly polarized 10.6-\ensuremath{\mu}m radiation. Photodetachment angular distributions and total transition probabilities are examined for explicit intensity effects. It is found that total transition probability $W$ is not sensitive to intensity since $\frac{d(logW)}{d}$ ($logz$) retains low-intensity straight-line behavior up to quite high values of $z$. An important intensity effect is the major significance of higher-than-lowest-order terms when $z$ is large, especially for circular polarization. A sensitive indicator of intensity is the ratio of photodetachment probabilities in circularly and linearly polarized fields, which increases sharply with intensity. An investigation of the convergence of perturbation expansions gives the upper limit $zl[\frac{{E}_{B}}{\ensuremath{\omega}}]\ensuremath{-}\frac{{E}_{B}}{\ensuremath{\omega}}$, where the square bracket means "smallest integer containing" the quantity in brackets. This limit is $zl0.59$ for ${\mathrm{H}}^{\ensuremath{-}}$ in 10.6-\ensuremath{\mu}m radiation. The failure of perturbation theory is not necessarily manifest in qualitative ways. For example, it is not apparent in total photoelectron yield as a function of intensity.

Transient Response of Multiconductor Transmission Lines Excited by a Nonuniform Electromagnetic Field

Abstract: The time-domain transmission-line equations for uniform multiconductor transmission lines in a conductive, homogeneous medium excited by a transient, nonuniform electromagnetic (EM) field, are derived from Maxwell's equations. Depending on how the line voltage is defined, two formulations are possible. One of these formulations is considerably more convenient to apply than the other. The assumptions made in the derivation of the transmission-line equations and the boundary conditions at the terminations are discussed. For numerical calculations, the transmission -line equations are represented by finite-difference techniques, and numerical examples are included.

Role of Anisotropic Exchange Interactions in Determining the Properties of Spin-Glasses

Abstract: Recent measurements on $\mathrm{Cu}\mathrm{Mn}$ spin-glass alloys have revealed that the anisotropy field maintaining the remanent magnetization in the direction of the initial applied field is strongly enhanced by the addition of nonmagnetic Au or Pt impurities. We show that these results can be accounted for by the existence of Dzyaloshinsky-Moriya-type interactions between the Mn spins arising from spin-orbit scattering of the conduction electrons by nonmagnetic impurities. The magnitude of these interactions is surprisingly large.

Some New Mathematical Methods for Variational Objective Analysis Using Splines and Cross Validation

Abstract: Let Φ(x,y,p,t) be a meteorological field of interest, say, height, temperature, a component of the wind field, etc. We suppose that data concerning the field of the form ΦI = LiΦ + ϵi are where each Li is an arbitrary continuous linear functional and ϵi is a measurement error. The data Φi may be the result of theory, direct measurements, remote soundings or a combination of these. We develop a new mathematical formalism exploiting the method of Generalized Cross Validation (GCV), and some recently developed optimization results, for analyzing this data. The analyzed field ΦN,m,λ is the solution to the minimization problem: Find Φ in a suitable space of functions to minimize where Functions of d=1, 2 or 3 of the four variables x, y, p, t are also considered. The approach can he used to analyze temperature fields from radiosonde-measured temperatures and satellite radiance measurements simultaneously, to incorporate the geostrophic wind approximation and other information. In a test of the method (...

Seismic Migration: Imaging of Acoustic Energy by Wave Field Extrapolation

Abstract: Introduction. 1. Basic Concepts. 2. Principles of Seismic Inversion. 3. User-Oriented Discussion on Seismic Migration Technique. 4. Choice of the Proper Migration Technique. 5. Influence of Velocity Errors. 6. Influence of Errors in the Input Data. 7. Effect of Field Patterns on the Migration Result. 8. Interpretive Migration. Appendices. Subject Index.

Reversed-field-pinch research

Abstract: Theoretical and experimental research in the reversed-field pinch (RFP) is reviewed. In this system, Bθ ~ B, q 10% has been observed. Following a historical review of pinch research, the basic theoretical properties of the RFP are established including the equilibrium, toroidal displacement, diffusion and confinement; studies of ideal and dissipative MHD stability theory are then described. Experimental and theoretical work on relaxation and self-reversal, the process whereby an RFP distribution can be set up spontaneously and subsequently sustained, is presented and discussed. There follows a general account of RFP experiments. These are divided into 'fast experiments', which utilize small-bore insulating tori in which the distribution is usually set up by fast programming on microsecond timescales, and 'slow experiments', carried out in large metal-walled tori in which the field configuration is set up slowly by self-reversal on millisecond timescales. A brief account of RFP reactor studies and of new and future experiments is then given, followed finally by a general discussion in which the main conclusions are presented.

Quantum theory of optical bistability. I. Nonlinear polarisability model

Abstract: A quantum treatment of a coherently driven dispersive cavity is given based on a cubic nonlinearity in the polarisability of the internal medium. This system displays bistability and hysteresis in the semiclassical solutions. Quantum fluctuations are included via a Fokker-Planck equation in a generalised P representation. The transmitted light shows a transition from a single-peaked spectrum to a double-peaked spectrum above the threshold of the lower branch. Fluctuations in the field are reduced on the upper branch and both photon bunching and photon antibunching are predicted, for different operating points. An exact solution obtained for the steady-state generalised P function shows decidedly non-equilibrium behaviour, e.g. the lack of a Maxwell construction.

Geometrical Theory of Diffraction for Electromagnetic Waves

Abstract: The continuous development of the Geometrical Theory of Diffraction (GTD), from its conception in the 1950s, has now established it as a leading analytical technique in the prediction of high-frequency electromagnetic radiation and scattering phenomena. Consequently, there is an increasing demand for research workers and students in electromagnetic waves to be familiar with this technique. In this book they will find a thorough and clear exposition of the GTD formulation for vector fields. It begins by describing the foundations of the theory in canonical problems and then proceeds to develop the method to treat a variety of circumstances. Where applicable, the relationship between GTD and other high-frequency methods, such as aperture field and the physical optics approximation, is stressed throughout the text. The purpose of the book, apart from expounding the GTD method, is to present useful formulations that can be readily applied to solve practical engineering problems. To this end, the final chapter supplies some fully worked examples to demonstrate the practical application of the GTD techniques developed in the earlier chapters.

Quantum topology of molecular charge distributions. III. The mechanics of an atom in a molecule

Abstract: The variation of the atomic action integral yields Schrodinger’s equations‐of‐motion and an atomic statement of the variational principle. The atom and its average properties are defined by the variational principle together with the requirement that they satisfy the Heisenberg equation‐of‐motion. Schrodinger’s equations define the components of the energy‐momentum tensor. The divergence equations satisfied by the spatial components of this tensor, the stress tensor, yield an expression for the resultant force exerted on a single electron at a given point in space and at a given time by the average motion of the other particles in the system. The integration of this force density over the space of an atom yields an equation‐of‐motion for an atom in a molecule identical to that determined by the generalized variational principle. Thus the action principle yields a local description of the mechanical properties of an atom and a definition of their average values. The force density is expressible in terms of a stress tensor which is a functional of the first‐order density matrix. The virial of this force yields the potential energy density of a single electron moving in the average field generated by the motion of the other particles in the system. This enables one to define the total energy density as a functional of the first‐order density matrix. The atomic average of this energy density is identical to the average energy of an atom in a molecule as defined through the atomic statement of the variational principle. The energy density defined in this manner has the essential property of predicting that if the distribution of charge for an atom is identical in two different systems or at different sites within a given system (e.g., a solid) then the atom will contribute identical amounts to the total energy in both instances. Matter is manifest in real space through its distribution of charge. Those properties of matter which are extensive are so as a consequence of the periodicity of the charge distribution at the atomic level. The equivalence of the quantum mechanical definition of an atom with that determined by the topological properties of the charge distribution is demonstrated. It is shown that the special properties possessed by the atomic action integral are a direct consequence of the topological definition of an atom as the union of an attractor and its basin. The relationship between the topological and mechanical properties of the charge density is pursued through a study of the topological properties of the first‐order density matrix. As demonstrated, the properties of the first‐order matrix determine both the topology and the mechanics of the charge density.

Charged macromolecules in external fields. I. The sphere

Abstract: The response of rigid macroions in aqueous solution to an external electric field is considered. The external field, which may be steady or oscillating, induces perturbations in the distribution of coions and counterions, and also in the electrical and solvent velocity fields. The basic equations that describe the various fields are reviewed, and then specialized to the special problem of thin double layers. Boundary conditions are derived which differ from those used in previous work. Previous treatments of the counterion flux into the double layer have either omitted the flux, or taken it to be in phase with the applied field. We find that this flux is large, and has a significant component out of phase. The new boundary conditions make substantial changes in the complex dielectric response. The dominant slow process that controls relaxation is the slow diffusion of neutral salt in the environment of the macromolecule. Large perturbations are induced in the neutral salt concentration by charge distortio...

Transient response of multiconductor transmission lines excited by a nonuniform electromagnetic field

Abstract: The time-domain transmission-line equations for uniform multiconductor transmission lines in a conductive, homogeneous medium excited by a transient, nonuniform electromagnetic (EM) field, are derived from Maxwell's equations. Depending on how the line voltage is defined, two formulations are possible. One of these formulations is considerably more convenient to apply than the other. The assumptions made in the derivation of the transmission-line equations and the boundary conditions at the terminations are discussed. For numerical calculations, the transmission -line equations are represented by finite-difference techniques, and numerical examples are included.

Experimental derivation of the source and drain resistance of MOS transistors

Abstract: A new method for experimentally deriving the source-and-drain resistance of MOS transistors is presented along with experimental results verifying its accuracy. The method also yields the mobility reduction with high gate-oxide field. The measurements are done on two (or more) MOS transistors which are identical except that their gate lengths differ by a known amount.

Discharge current induced by the motion of charged particles

Abstract: A formula for discharge current flowing in a space charge filled gap is derived for a general geometry of electrodes from the energy balance equation in which the displacement current caused by the motion of the charged particles in the gap is taken into account. It is found that in the formula obtained the influence of the field component produced by the space charge does not appear explicitly and the formula is compatible with the principle of superposition.

Magnetic resonance apparatus

Abstract: Means for producing a region of homogeneous magnetic field remote from the source of the field, wherein two equal field sources are arranged axially so their fields oppose, producing a region near the plane perpendicular to the axis midway between the sources where the radial component of the field goes through a maximum. Near the maximum, the field is homogeneous over prescribed regions.

Modified Sternheimer equation for polarizability

Abstract: The Sternheimer equation for atomic polarizability is modified to account for the self-consistent field. The equations are quite simple for closed-shell ions. Numerical results are presented.

Post-Ionization of Field-Evaporated Ions

Abstract: It is shown that the final observed charge state of a field-evaporated ion can be explained by the occurrence of post-ionization whereby an ion being accelerated away from a metal surface in a strong electric field loses one or more electrons by tunneling into the substrate. Calculations using an approximate analytic formula derived from a simple model potential predict the probability of post-ionization for many different elements.

The collimating and magnifying properties of a superconducting field photoelectron spectrometer

Abstract: An analysis is given of the possible advantages of a photoelectron spectrometer based upon the properties of the axially symmetric inhomogeneous magnetic field of a superconducting solenoid The consequences of electron motion along the solenoid axis are discussed and it is shown that this can lead to a novel high-resolution method of electron energy analysis together with the possibility of photoelectron microscopy

A field investigation of the relationship between oscillation ripple spacinng and the near-bottom water orbital motions

Abstract: Measurements of oscillation ripples have been obtained in the high-energy wave environment off the Oregon coast, and in the relatively mild summer-wave environment near Fisher's Island, New York. Scuba-equipped divers measured ripple characteristics while the simultaneous causative near-bottom orbital motions were determined from a wave pressure transducer and electromagnetic current meter mounted near the bottom. The data collected in this study, together with previously published field measurements of oscillation ripples, are compared with empirical relationships for ripple geometry based on laboratory data. As expected, the field data are more scattered than the laboratory data. Reasons for this scatter include several wave spectral effects, ocean waves in the study areas having wi e spectra in contrast to the simple harmonic motions of the laboratory devices. Any selected trend that relates the ripple spacing to the wave orbital motions must take into consideration this spectrum and the manner in which the orbital parameters are defined. Orbital parameters calculated from a significant wave height were found to give the best comparison with the laboratory results.

''Gauge'' form of description of massless fields with arbitrary spin

Abstract: A new form of description of free massless fields with arbitrary spin s(s> or =3/2), using nonsymmetric tensors and spin-tensors analogous to the tetrad field in gravitation, is proposed. In these terms, N = 1 supersymmetry transformations for the multiplets (s, s+1/2) are obtained. The properties of the antisymmetric spin-tensors are discussed.

Classical electrodynamics of retarded fields and point particles

Abstract: Some developments of classical particle electrodynamics are discussed by means of an approach based on retarded Lienard-Wiechert field. A description of radiation throughout space-time is obtained, which is more satisfactory than the one based on a superposition of advanced and retarded fields.

An Objective Analysis Technique for Constructing Three-Dimensional Urban-Scale Wind Fields

Abstract: An objective analysis procedure for generating mass-consistent, urban-scale three-dimensional wind fields is presented together with a comparison against existing techniques. The algorithm employs terrain following coordinates and variable vertical grid spacing. Initial estimates of the velocity field are developed by interpolating surface and upper level wind measurements. A local terrain adjustment technique, involving solution of the Poisson equation, is used to establish the horizontal components of the surface field. Vertical velocities are developed from successive solutions of the continuity equation followed by an iterative procedure which reduces anomalous divergence in the complete field. Major advantages of the procedure are that it is computationally efficient and allows boundary values to adjust in response to changes in the interior flow. The method has been successfully tested using field measurements and problems with known analytic solutions.