Showing papers on "Field (physics) published in 1984"
TL;DR: In this article, a time-dependent version of density functional theory was proposed to deal with the non-perturbative quantum mechanical description of interacting many-body systems moving in a very strong timedependent external field.
Abstract: The response of an interacting many-particle system to a time-dependent external field can usually be treated within linear response theory. Due to rapid experimental progress in the field of laser physics, however, ultra-short laser pulses of very high intensity have become available in recent years. The electric field produced in such pulses can reach the strength of the electric field caused by atomic nuclei. If an atomic system is placed in the focus of such a laser pulse one observes a wealth of new phenomena [1] which cannot be explained by traditional perturbation theory. The non-perturbative quantum mechanical description of interacting particles moving in a very strong time-dependent external field therefore has become a prominent problem of theoretical physics. In principle, it requires a full solution of the time-dependent Schrodinger equation for the interacting many-body system, which is an exceedingly difficult task. In view of the success of density functional methods in the treatment of stationary many-body systems and in view of their numerical simplicity, a time-dependent version of density functional theory appears highly desirable, both within and beyond the regime of linear response.
6,874 citations
TL;DR: In this article, the authors present theory and extended experimental results for the large shift in optical absorption in GaAs-AlGaAs quantum well structures with electric field perpendicular to the layers.
Abstract: We present theory and extended experimental results for the large shift in optical absorption in GaAs-AlGaAs quantum well structures with electric field perpendicular to the layers. In contrast to the Stark effect on atoms or on excitons in bulk semiconductors, the exciton resonances remain resolved even for shifts much larger than the zero-field binding energy and fields g 50 times the classical ionization field. The model explains these results as a consequence of the quantum confinement of carriers.
1,604 citations
TL;DR: In this article, a volume integral equation is formulated and solved by using the method of moments for calculating the electromagnetic scattering from and internal field distribution of arbitrarily shaped, inhomogeneous, dielectric bodies.
Abstract: A method for calculating the electromagnetic scattering from and internal field distribution of arbitrarily shaped, inhomogeneous, dielectric bodies is presented. A volume integral equation is formulated and solved by using the method of moments. Tetrahedral volume elements are used to model a scattering body in which the electrical parameters are assumed constant in each tetrahedron. Special basis functions are defined within the tetrahedral volume elements to insure that the normal electric field satisfies the correct jump condition at interfaces between different dielectric media. An approximate Galerkin testing procedure is used, with special care taken to correctly treat the derivatives in the scalar potential term. Calculated internal field distributions and scattering cross sections of dielectric spheres and rods are compared to and found in agreement with other calculations. The accuracy of the fields calculated by using the tetrahedral cell method is found to be comparable to that of cubical cell methods presently used for modeling arbitrarily shaped bodies, while the modeling flexibility is considerably greater.
887 citations
01 Jan 1984
486 citations
TL;DR: In this paper, it is suggested that the apparent cosmological constant is not necessarily zero but that zero is by far the most probable value, and that the action of solutions of the euclidean field equations is most negative.
474 citations
01 Jan 1984
TL;DR: The fundamental equations of the electrodynamics of continuous media are obtained by averaging the equations for the electromagnetic field in a vacuum as discussed by the authors, and the form of the equations and significance of the quantities appearing in them depend on the physical nature of the medium and on the way in which the field varies with time.
Abstract: Macroscopic electrodynamics is concerned with the study of electromagnetic fields in space that is occupied by matter. Electrodynamics deals with physical quantities averaged over elements of volume that are physically infinitesimal and ignore the microscopic variations of the quantities that result from the molecular structure of matter. The fundamental equations of the electrodynamics of continuous media are obtained by averaging the equations for the electromagnetic field in a vacuum. The form of the equations of macroscopic electrodynamics and the significance of the quantities appearing in them depend on the physical nature of the medium and on the way in which the field varies with time. Charges present in a conductor must be located on its surface. The presence of charges inside a conductor would cause an electric field in it. These charges can be distributed on its surface, however, in such a way that the fields that they produce in its interior are mutually balanced. The mean field in the vacuum is almost the same as the actual field. The two fields differ only in the immediate neighborhood of the body, where the effect of the irregular molecular fields is noticeable, and this difference does not affect the averaged field equations.
473 citations
TL;DR: The range of magnetic field amplitudes tested encompass the geomagnetic field, suggesting the possibility of mutagenic interactions directly arising from short-term changes in the earth's field.
Abstract: Human fibroblasts have exhibited enhanced DNA synthesis when exposed to sinusoidally varying magnetic fields for a wide range of frequencies (15 hertz to 4 kilohertz) and amplitudes (2.3 X 10(-6) to 5.6 X 10(-4) tesla). This effect, which is at maximum during the middle of the S phase of the cell cycle, appears to be independent of the time derivative of the magnetic field, suggesting an underlying mechanism other than Faraday's law. The threshold is estimated to be between 0.5 X 10(-5) and 2.5 X 10(-5) tesla per second. These results bring into question the allegedly specific magnetic wave shapes now used in therapeutic devices for bone nonunion. The range of magnetic field amplitudes tested encompass the geomagnetic field, suggesting the possibility of mutagenic interactions directly arising from short-term changes in the earth's field.
379 citations
TL;DR: In this paper, a supersymmetric self-dual model for spacetime dimension d = 4 k − 1 was presented, which propagates half as many massive modes as the original tensor model.
354 citations
01 Jan 1984
TL;DR: A systematic way of stabilizing finite element approximation of the Stokes equations by adding bubble functions to the discrete velocity field is presented.
Abstract: Consider finite element approximation of the Stokes equations. We present a systematic way of stabilizing it by adding bubble functions to the discrete velocity field. Another way of stabilization is also presented where the finite element spaces are kept unchanged but the discrete incompressibility condition is modified instead.
TL;DR: In this paper, the authors used linear perturbation theory to show that the reflection coefficient is both oscillatory in the quotient of the length of the patch and the surface wavelength, and also strongly dependent upon the quotients of the surface and bed wavelengths.
Abstract: Surface waves travelling in water of finite depth may be scattered by a region of undulating bottom topography. The present study is concerned with the idealized two-dimensional situation in which long-crested surface waves are incident upon a patch of long-crested regular bottom ripples. The principal question examined concerns the amount of incident wave energy that is reflected by the ripple patch. Linear perturbation theory is used to show that the reflection coefficient is both oscillatory in the quotient of the length of the patch and the surface wavelength, and also strongly dependent upon the quotient of the surface and bed wavelengths. In particular, there is a Bragg resonance between the surface waves and the ripples, which is associated with the reflection of incident wave energy. A secondary question concerns the nature of the wave field in the immediate vicinity of the ripple patch. In resonant cases, it is shown how the partially standing wave on the upwave side of the ripple patch gives way, in an almost linear manner over the patch itself, to a progressive transmitted wave on the downwave side. The theoretical predictions are compared with an extensive set of laboratory observations made in a wave tank. Comparisons relating both to the reflection coefficient, and also to the wave field over the ripple patch, are shown to give consistently good agreement. Finally, the implications of the results for sediment transport on an erodible bed are examined.
TL;DR: In this article, the absorption spectrum of a system of $N$ atoms interacting with a single mode of the quantized radiation field is exactly calculated, and such a spectrum shows vacuum-field Rabi splittings.
Abstract: The absorption spectrum of a system of $N$ atoms interacting with a single mode of the quantized radiation field is exactly calculated. Such a spectrum shows vacuum-field Rabi splittings, and thus microwave absorption by Rydberg atoms in a cavity should be a useful way to observe these splittings.
TL;DR: In this article, the Redlich-Kister equation has been used to model the CMAS system and the enstatite-diopside join of Lindsley et al. and Gasparik and Newton.
Abstract: In the system CaO-MgO-Al2O3-SiO2 (CMAS), equilibrium alumina contents of orthopyroxene and clinopyroxene, both coexisting with spinel + forsterite or spinel + anorthite, have been reversed in 16 runs at 1,300–1,400°C and 10.2–20.8 kbar, using PbO flux. The present data and the data of Perkins and Newton (1980) have been modeled using the Redlich-Kister equation. The resulting model satisfies most of the reversed data in the CMAS system, agrees very well with thermochemical measurements, and is consistent with the model for the enstatite-diopside join of Lindsley et al. (1981) and with the system MgO-Al2O3-SiO2 of Gasparik and Newton (1984). The present data, however, do not confirm the negative slopes of Al-isopleths in the spinel lherzolite field suggested by Dixon and Presnall (1980). The new model has been used to calculate a graphical two-pyroxene thermobarometer applicable to natural two-pyroxene assemblages closely approaching in composition the CMAS system.
TL;DR: In this paper, the authors used gas chromatography to study the concentration field in compressible sonic jets of natural gas over the pressure range from 2 to 70 bar and showed that the behavior of such underexpanded jets is similar to classical free jets provided that an appropriate scaling factor is employed to describe the effective size of the jet source.
Abstract: The concentration field in compressible sonic jets of natural gas over the pressure range from 2 to 70 bar has been studied using gas chromatography. At these pressures the jet expands immediately downstream of the nozzle in order to equilibriate with ambient conditions. The behaviour of such underexpanded jets is shown to be similar to classical free jets provided that an appropriate scaling factor is employed to describe the effective size of the jet source. This notional source is referred to as the pseudo-diameter and a theroretical analysis for its derivation is presented. The experimental data support this approach, and the decay constants for the jet concentration field agree with previous measurements in incompressible jets. Comparison with results obtained from a high pressure jet of ethylene at 8 bar indicate that the effect of jet fluid density in concentration decay is the same as in classical free jets.
TL;DR: In this paper, the energy values of many low-lying states of the one-electron problem in the presence of a homogeneous magnetic field of arbitrary strength (0
Abstract: The energy values of many low-lying states of the one-electron problem in the presence of a homogeneous magnetic field of arbitrary strength (0
TL;DR: In this paper, a mathematical formulation for the transient development of the fluid-flow field and the temperature field in a liquid pool, generated by a spatially variable heat flux falling on an initially solid metal block, is presented.
Abstract: A mathematical formulation is presented for the transient development of the fluid-flow field and the temperature field in a liquid pool, generated by a spatially variable heat flux falling on an initially solid metal block. This physical situation is an idealized representation of a TIG (tungsten-inert-gas) welding process. In the formulation allowance is made for electromagnetic, buoyancy and surface forces and the resultant equations are solved numerically.It is found that both the convective flow field and the temperature field are markedly affected by the nature of the heat flux and the flux of electric current falling on the free surface.In the absence of surface-tension effects a broadly distributed heat flux and corresponding current distribution cause a situation where both electromagnetic and buoyancy forces are important in determining the fluid-flow field; however, in these systems the fluid-flow field does not play a significant role in defining the heat-transfer process. In contrast, a sharply focused heat flux and current density on the free surface give rise to strong electromagnetically driven flows, which play an important role in determining the shape of the weld pool.Calculations are also done exploring the effect of surface-tension-driven flows. It is found that surface-tension gradients may produce quite high surface velocities and can have a profound effect on determining the weld-pool shape.
TL;DR: In this paper, the exact distributed image current function is obtained for the classical Sommerfeld half-space problem with vertical magnetic current source in complex space by applying the Laplace transform.
Abstract: Applying the Laplace transform, the exact distributed image current function is obtained for the classical Sommerfeld half-space problem with vertical magnetic current source. The resulting field integral is well behaved when the image current is situated in complex space. Unlike previous approximate images, the present theory is valid for any distance, height of the source, frequency, and half-space parameters. It is demonstrated that the present image theory reduces to the well-known dipole image at complex depth for large dielectric parameters of the half-space. Also, the reflection-coefficient method is obtained as a farfield approximation. Calculation of fields through exact image integration is seen to be simple and accurate and require modest computer capacity and time. In an appendix, some properties of the multivalued Green's function arising from a dipole source in complex space are also studied.
TL;DR: In this paper, the baryon density for quarks coupled to a chiral field with a hedgehog shape was calculated and shown to be very similar to that of a skyrmion.
TL;DR: In this paper, a numerical method for time-stepping Maxwell's equations in the two-dimensional (2-D) TE mode, which in a conductive earth reduces to the diffusion equation, is described.
Abstract: We describe a numerical method for time‐stepping Maxwell’s equations in the two‐dimensional (2-D) TE‐mode, which in a conductive earth reduces to the diffusion equation. The method is based on the classical DuFort‐Frankel finite‐difference scheme, which is both explicit and stable for any size of the time step. With this method, small time steps can be used at early times to track the rapid variations of the field, and large steps can be used at late times, when the field becomes smooth and its rates of diffusion and decay slow down. The boundary condition at the earth‐air interface is handled explicitly by calculating the field in the air from its values at the earth’s surface with an upward continuation based on Laplace’s equation. Boundary conditions in the earth are imposed by using a large, graded grid and setting the values at the sides and bottom to those for a haft‐space. We use the 2-D model to simulate transient electromagnetic (TE) surveys over a thin vertical conductor embedded in a half‐space...
Journal Article•
TL;DR: In this paper, a theory for the statics and slow dynamics of convective rolls encountered in large aspect ratio Rayleigh-Benard boxes is developed, which includes the notion of Busse stability balloon, reduces near critical values of the stress parameter to the Newell-Whitehead-Segel equations, and contains the Pomeau-Manneville phase equation.
TL;DR: In this article, the interference of passive thermal fields produced by two (and more) line sources in decaying grid turbulence is studied by using the inference method described by Warhaft (1981) to determine the cross-correlation coefficient ρ between the temperature fluctuations produced by the sources.
Abstract: The interference of passive thermal fields produced by two (and more) line sources in decaying grid turbulence is studied by using the inference method described by Warhaft (1981) to determine the cross-correlation coefficient ρ between the temperature fluctuations produced by the sources. The evolution of ρ as a function of downstream distance, for 0.075 < d/l < 10, where d is the wire spacing and l is the integral lengthscale of the turbulence, is determined for a pair of sources located at various distances from the grid. It is found that ρ may be positive or negative (thereby enhancing or diminishing the total temperature variance) depending on the line-source spacing, their location from the grid and the position of measurement. It is also shown that the effects of a mandoline (Warhaft & Lumley 1978) may be idealized as the interference of thermal fields produced by a number of line sources. Thus new light is shed on the rate of decay of scalar-variance dissipation. The thermal field of a single line source is also examined in detail, and these results are compared with other recent measurements.
TL;DR: In this article, it is shown that the Coriolis force will probably dominate the force budget at the top of the core and that, in such a case, the motion of the fluid involves the two parts of the field in a different way; in particular, the existing axial dipolar component is not reengaged in the process which builds up the SV.
Abstract: In studies of the temporal variations of the main internal geomagnetic field (the secular variation or SV), it is usual to consider separately the variations of the dipolar and non-dipolar parts which appear to have different time constants. The mechanism that is generally invoked to explain the generation of SV is the advection of the lines of force of the main field by the highly conducting fluid at the top of the core. Such a mechanism involves the main field as a whole and it is not clear a priori why its two parts should behave separately. I show here that the Coriolis force will probably dominate the force budget at the top of the core and that, in such a case, the motion of the fluid involves the two parts of the field in a different way; in particular, the existing axial dipolar component is not re-engaged in the process which builds up the SV.
TL;DR: In this article, a moment solution to the electric field integral equation on the surface is presented for the electric current and electric charge induced on a perfectly conducting surface illuminated by an incident electromagnetic field.
Abstract: A new E -field solution is presented for the electric current and electric charge induced on a perfectly conducting surface illuminated by an incident electromagnetic field. This solution is a moment solution to the electric field integral equation on the surface. The expansion functions consist of a set of functions suitable for expanding the magnetostatic current and a set of functions whose surface divergences are suitable for expanding the electrostatic charge. The testing functions are similar to the expansion functions. With these expansion and testing functions, the new E -field solution works well with surfaces whose maximum dimension may be as small as 10^{-15} wavelengths or as large as a few wavelengths. Previous E -field solutions begin to deteriorate when the maximum dimension of the surface falls below a few hundredths of a wavelength. The new E -field solution is applied to a conducting circular disk and a conducting sphere.
TL;DR: In this paper, the authors used the principles of optimal linear estimation to obtain a quantitative estimate of the field of mean motion (FOM) of the sea ice in the last 100 station-year drift data.
Abstract: The observational basis for our understanding of sea ice motion comes from the trajectories of particular ice floes. These ice floes may have been marked by a manned research station or, more recently, by an automatic data buoy. Since 1893, almost 100 station-years of drift data have been recorded. Using the principles of optimal linear estimation, these data are used to obtain a quantitative estimate of the field of mean motion.
TL;DR: In this article, the transport coefficients are expressed by real-time correlation functions of energy-momentum tensor in the linear response approximation, and a field theoretical method to compute them in perturbation theory is demonstrated in λϕ4 theory.
TL;DR: In this article, it was shown that a magnetic field is asymptotically (t → ∞) decaying in a flow of finite conductivity with v = Cr, where C = Cζ(t) is a random matrix.
Abstract: A magnetic field is shown to be asymptotically (t → ∞) decaying in a flow of finite conductivity with v = Cr, where C = Cζ(t) is a random matrix. The decay is exponential, and its rate does not depend on the conductivity. However, the magnetic energy increases exponentially owing to growth of the domain occupied by the field. The spatial distribution of the magnetic field is a set of thin ropes and (or) layers.