Showing papers on "Electric field published in 1988"

Spatial variation of currents and fields due to localized scatterers in metallic conduction

Abstract: Localized scatterers can be expected to give rise to spatial variations in the electric field and in the current distribution. The transport equation allowing for spatial variations is solved by first considering the homogeneous transport equation which omits electric fields. The homogeneous solution gives the purely diffusive motion of current carriers and involves large space charges. The electric field is then found, and approximate space charge neutrality is restored, by adding a particular solution of the transport equation in which the electric field is associated only with space charge but not with a current. The presence of point scatterers leads to a dipole field about each scatterer. The spatial average of a number of these dipole fields is the same as that obtained by the usual approach which does not explicitly consider the spatial variation. Infinite plane obstacles with a reflection coefficient r are also considered. These produce a resistance proportional to r/(1-r).

Mapping electrodynamic features of the high-latitude ionosphere from localized observations: technique

Abstract: This paper describes a novel procedure for mapping high-latitude electric fields and currents and their associated magnetic variations, using sets of localized observational data derived from different types of measurements. The technique provides a formalism for incorporating simultaneously such different classes of data as electric fields from radars and satellites, electric currents from radars, and magnetic perturbations at the ground and at satellite heights; the technique also uses available statistical information on the averages and variances of electrodynamic fields. The technique provides a more rigorous way of quantitatively estimating high-latitude electric field and current patterns than other methods and has a capability to quantify the errors in the mapped fields, based on the distribution of available data, their errors, and the statistical variances of the fields. The technique is illustrated by an application to a substorm which was analyzed by Kamide et al. (1982) by an earlier technique.

Model of L- to H-mode transition in tokamak.

Abstract: A new model of $L$- to $H$-mode transition in tokamak plasmas is presented. Nonambipolar particle losses determine the consistent radial electric field near plasma periphery. A "cusp-type catastrophe" among the radial electric field, particle flux, and edge gradients is found. At the transition, plasma loss can take multiple values for one profile of density and temperature near the edge. A critical edge condition for the transition is obtained.

General magnetic reconnection, parallel electric fields, and helicity

Abstract: This paper considers the concept of magnetic reconnection from a general point of view, with special consideration given to magnetic reconnection in nonvanishing magnetic fields, i.e., finite-B reconnection as distinct from zero-B reconnection. It is shown that the electric field component parallel to the magnetic field (E-parallel) plays a crucial physical role in finite-B reconnection. Two theorems involving E-parallel are proposed. The first defines a necessary and sufficient condition of E-parallel for global reconnection to occur. The second theorem is concerned with the change of magnetic helicity to E-parallel for cases where the electric field vanishes at large distances. The general magnetic reconnection concept is tested by applying it to the process of plasmoid formation process.

Static shift of magnetotelluric data and its removal in a sedimentary basin environment

Abstract: Previous modeling investigations of the static shift of magnetotelluric (MT) apparent resistivity curves have limited appeal in that the electric fields used were point measurements, whereas field observations are of voltage differences. Thus, inhomogeneities of dimension of the order of the electrode line length could not be investi­ gated. In this paper, by using a modeling algorithm that derives point voltages rather than point electric fields, I consider the effect on the MT responses of local near­ surface distorting structures, which are both outside of, and inside, the telluric electrode array. I show that static-shift effects are of larger spatial size but of less magnitude than would be expected from conventional modeling. Also, the field observation that static shift affects only the apparent resistivity curve but not the phase response can be replicated by the voltage differ­ ence modeling. If there exists within the earth a layer whose variation in electrical resistivity along the profile can be treated in a parametric fashion, then static shift of the apparent resistivity curves can be corrected. Deriving the modal value from a sufficient number of observations for the layer resistivity is the most useful approach.

Electro-acoustic effects in a dilute suspension of spherical particles

Abstract: Sound waves can be generated in a colloid by the application of an alternating electric field. In this paper we describe the method for calculating this and the related electro-acoustic phenomenon of electric fields generated by sound waves. As an illustration of the procedure, we obtain formulae for these two effects for a suspension of spherical particles with thin double layers, in a parallel plate geometry.

Electric-field-induced localization and oscillatory electro-optical properties of semiconductor superlattices.

Abstract: We show that the application of an electric field $F$ along the growth axis of a semiconductor superlattice results in a strong localization of the eigenstates, a blue shift of the optical-absorption edge, and the presence of oscillations periodic in ${F}^{\ensuremath{-}1}$. These unique electro-optical properties are derived here within the framework of a tight-binding description of the envelope functions and also from numerical solutions of the Schr\"odinger equation for a finite set of coupled quantum wells.

Semiconductor devices exhibiting minimum on-resistance

Abstract: An improved conductivity vertical channel semiconductor device includes an insulated gate electrode disposed adjacent a substantial portion of the voltage supporting region. In response to an appropriate bias, the control electrode couples to the electric field originating on charges within the voltage supporting region to reorient the electric field associated with those charges toward the gate electrode and transverse to the direction of current flow through the device. Improved control of the electric field within the voltage supporting region allows the doping concentration, and hence the conductivity of the channel, to be improved without a concomitant decrease in breakdown voltage. Accordingly, the channel width and cell repeat distance of the improved device can be reduced, allowing for an improved current density to be established throughout an overall device cell structure. The charge control region of the voltage supporting layer exhibits an aspect ratio of 0.5.

Internal and near‐surface electromagnetic fields for a spherical particle irradiated by a focused laser beam

Abstract: Theoretical expressions for the internal and external electromagnetic fields for an arbitrary electromagnetic beam incident upon a homogeneous spherical particle are derived, and numerical calculations based upon this theoretical development are presented. In particular, spatial distributions of the internal and near‐surface electric field magnitude (source function) for a focused fundamental (TEM00 mode) Gaussian beam of 1.06 μm wavelength and 4 μm beam waist diameter incident upon a 5‐μm‐diam water droplet in air are presented as a function of the location of the beam focal point relative to the sphere center. The calculations indicate that the internal and near‐surface electric field magnitude distribution can be strongly dependent upon relative focal point positioning and may differ significantly from the corresponding electric field magnitude distribution expected from plane‐wave irradiation.

Thermionic emission and Gaussian transport of holes in a GaAs/AlxGa1-xAs multiple-quantum-well structure.

Abstract: We present and test a modified thermionic emission model for time-resolved charge-carrier transport perpendicular to the layers of multiple quantum-well structures in an electric field. The predictions of the model on the nature (Gaussian transport) and the dynamics (transport times, field dependence of the mobility) of carrier transport agree favorably with our experiments performed for the case of holes and allow an accurate determination of the band offset.

Reduction of kink effect in thin-film SOI MOSFETs

Abstract: Numerical simulation is used to show that potential and electric field distribution within thin, fully depleted SOI devices is quite different from that observed within thicker, partially depleted devices. Reduction of drain electric field and of source potential barrier brings about a dramatic decrease of kink effect. >

Liquid crystal electro-optical device

Abstract: In a horizontal electric field drive type liquid crystal electro-optic device wherein a liquid crystal material is driven by controlling the strength of an electric field parallel to a substrate, noncontinuity of the electric field strength around each pixel electrode is minimized and thereby the occurrence of flaws in the orientation of the liquid crystal material and dispersion in operation are reduced and a construction having improved display characteristics and a method of manufacturing the same are provided. In a horizontal electric field drive type liquid crystal electro-optic device wherein a gate electrode 403, a source electrode 407, a drain electrode 408, a semiconductor film 406 and a common electrode 404 are formed on a glass substrate and a liquid crystal material is driven by controlling the strength of an electric field substantially parallel to the glass substrate, the electrodes and the semiconductor film are made curved, for example semi-circular or semi-elliptical, in sectional profile. These curved sectional profiles can be formed by suitably selecting and combining various patterning and etching methods.

Kinetic theory for electrostatic waves due to transverse velocity shears

Abstract: A kinetic theory in the form of an integral equation is provided to study the electrostatic oscillations in a collisionless plasma immersed in a uniform magnetic field and a nonuniform transverse electric field. In the low temperature limit the dispersion differential equation is recovered for the transverse Kelvin-Helmholtz modes for arbitrary values of K parallel, where K parallel is the component of the wave vector in the direction of the external magnetic field assumed in the z direction. For higher temperatures the ion-cyclotron-like modes described earlier in the literature by Ganguli, Lee and Plamadesso are recovered. In this article, the integral equation is reduced to a second-order differential equation and a study is made of the kinetic Kelvin-Helmholtz and ion-cyclotron-like modes that constitute the two branches of oscillation in a magnetized plasma including a transverse inhomogeneous dc electric field.

Photoelectric conversion device

Abstract: Disclosed is a photoelectric conversion device which comprises: a photoconductive layer (34, 44, 57, 67) made of amorphous semiconductor material which shows charge multiplication and which converts photo signals (37, 47, 50, 60) into electric signals; and a substrate (31, 41, 51, 61) having electric circuits or the like (32, 42, 56, 66) (for example switching elements) for reading the electric signals The amorphous semiconduc­tor material used according to the invention shows the charge multiplication action under predetermined intensity of electric field so that a high sensitive photoelectric conversion device having a gain which is not smaller than 1 is realized

Simultaneous density and electric field fluctuation spectra associated with velocity shears in the auroral oval

Abstract: A detailed study is presented of simultaneous density and electric field fluctuation spectra over a large-scale length range seen in association with large structured convective plasma flows, field-aligned currents, and particle precipitation at high latitudes. The data were obtained for two Dynamics Explorer 2 orbits at two different altitudes within the F region and the topside ionosphere. The observations are compared with results of nonlinear simulations of shear flow-driven instabilities and predictions based on two-dimensional turbulence arguments, with particular reference to the Kelvin-Helmholtz process.

Test particle acceleration in turbulent reconnecting magnetic fields

Abstract: The effect of turbulence on particle acceleration in a MHD field was investigated by computing test particle trajectories in turbulent MHD reconnecting fields, including reconnection simulations at different magnetic Reynolds numbers. The dynamics of individual particles were investigated making it possible to examine the acceleration mechanism in great detail. It was found that turbulence influences the acceleration in two ways. It enhances the reconnection electric field while producing a stochastic electric field that gives rise to momentum diffusion; and it produces magnetic 'bubbles' and other irregularities that can temporarily trap test particles in the strong reconnection electric field for times comparable to the magnetofluid characteristic time.

Kinetics of channelized membrane ions in magnetic fields

Abstract: The cyclotron resonance model for channel ion transport in weak magnetic fields is extended to include damping losses. The conductivity tensor is obtained for different electric field configurations, including the circuital field E phi normal to the channel axis. The conductivity behavior close to the cyclotron resonance frequency omega c is compared to existing Ca2+-efflux data in the literature. A collision time of .023 s results from this comparison under the assumption that K+ ions are transiting in a 0.35 G field. We estimate a mean kinetic energy of 3.5 eV for this ion at resonance. This model leads to discrete modes of vibration (eigenfrequencies) in the ion-lattice interaction, such that omega n = n omega c. The presence of such harmonics is compatible with recent results by Blackman et al. [1985b] and McLeod et al. [1986] with the interesting exception that even modes do not appear in their observations, whereas the present model has no restriction on n. This harmonic formalism is also consistent with another reported phenomenon, that of quantized multiple conductances in single patch-clamped channels.

Generating electromagnetic fields in a self regulating temperature heater by positioning of a current return bus

Abstract: A self-redulanting heater includes an electrically-conductive substrate (11), having a magnetic surface layer (13) of one skin depth, folded 180 degrees to define two heater sections joined by a fold section. The magnetic material has a considerably higher resistance than the substrate material. The surfaces of the two sections clad with the surface layer are in closely spaced parallel relation and connected in series by the fold section (23) such that a constant amplitude alternating energizing current flows in opposite directions through the two sections at any instant of time to thereby establish an electric field between the two heaters. The field concentrates current flow at the two facing surfaces. Depth of the current is determined by the skin effect phenomenon and increases significantly at temperatures above the Curie temperature of the magnetic material.

Indirect-direct anticrossing in GaAs-AlAs superlattices induced by an electric field: Evidence of Gamma -X mixing.

Abstract: We demonstrate that a GaAs-AlAs superlattice can be switched from indirect to direct, in both real and reciprocal spaces, by application of a modest axial electric field The crossover region is found to be an anticrossing, manifesting the presence of GAMMA-X mixing by a potential measured to be of the order of 1 meV This value is corroborated by time-decay measurements performed on different superlattices

A polarizable water model for calculation of hydration energies

Abstract: A molecular model for electronic polarization of water is defined, consisting of interacting point dipole polarizabilities in an electric field generated by atomic point charges, which represent the gasphase dipole moment of water molecules. The induced dipole equations are solved self consistently. The model has been implemented in a Monte Carlo hydration simulation program, and its computational performance is discussed. Results of calculations of hydration and protonation energies of amines (including glycine) are presented and discussed, together with results for the water dimer and for liquid water. Solvent induction appears significant to describe quantitatively solvent screening of interactions between charges on the solute. In combination with solvent polarization a quantum chemical charge model is found superior to an empirical set of charges. Inadequacies of the Lennard-Jones type modelling of non-electrostatic interactions between water molecules are demonstrated.

Simultaneous observation of upward moving field-aligned energetic electrons and ions on auroral zone field lines

Abstract: The authors present Viking observations of energetic electrons and ions which move upward along the magnetic field lines with energies of the same order of magnitude. The field-aligned particles are associated with a strong broadband low-frequency turbulence in the electric field and with downward Birkeland currents. They suggest that both ions and electrons are accelerated by a time-varying field-aligned electric field component. The downward field component accelerating the electrons upward is experienced as quasi-static by the electrons while they remain in the height-limited acceleration region. For the ions the fluctuating field is a wave field which has only a small translational effect on them.

Electroconformational coupling: how membrane-bound ATPase transduces energy from dynamic electric fields.

Abstract: Cells are constantly exposed to or surrounded by electric fields either from self-generating or from external sources. Proteins of cell membranes are thus subjected to influences by these electric fields; two of the most prominent electric fields are the in vivo surface and transmembrane potentials, which have magnitudes of 100-500 kV cm-I (see below). A protein molecule under such an intense electric field will behave quite differently than it would in an homogeneous aqueous solution. It is interesting to compare these values with the dielectric breakdown point of pure water, which is approximately 100 kV cm-I, Why a cell should actively maintain such large electric fields across its membranes is a theoretically interesting question since this requires sustained input of free energy. We propose that these fields serve many essential functions. Starting from the principles of thermodynamics, we summarize how an electric field can interact with a cell membrane and membrane proteins and 'The U.S, Government has the right to retain a nonexclusive royalty-free license in and to any copyright covering this paper,

Movement of blood cells in liquid by nonuniform traveling field

Abstract: A study of the motion of biological cells in aqueous solution using a traveling-field-type electric curtain device is performed. Cells driven by such a device undergo circular motions induced by the rotating traveling field, and as a result of field nonuniformity and drift in the direction of the wave propagation. Electrolytic dissociations of the aqueous medium are avoided by limiting the applied voltage below the theoretical dissociation voltage, while the field strength necessary for the actuation of the cell motion is insured by making the electrode dimensions as small as 100 mu m. The experiments are performed using sheep erythrocytes. The device shows a maximum performance with six-phase voltage of frequency 3 Hz and amplitude 1.5 V, where the transport of cells takes place without perceivable damage to the cells. >

Photodetachment of H- in an electric field.

Abstract: A simple analytic formula for the photodetachment cross section of H/sup -/ in an electric field is derived. The formula becomes identical to a formula derived many years ago in the vanishing-field limit. Three special features appear in the cross section in the presence of an electric field: a quantum tunneling effect, a new threshold law, and oscillations. These appear when the photon energy is, respectively, less than, equal to, or greater than the binding energy of H/sup -/. Enough information is provided in this paper so that one can calculate the cross section quickly.

Computer modeling of the electric field dependent absorption spectrum of multiple quantum well material

Abstract: The authors present a simple computer model for the electric field dependence of the absorption of semiconductor multiple-quantum-well (MQW) structure that will be used to optimize the performance of MQW modulators. This model has been compared to absorption spectra derived from photocurrent measurements on a GaAs/(GaAl)As MQW p-i-n diode and it has been found that the well-established Stark shifts of the exciton and subband continua energies are significantly overestimated. This might be linked to uncertainty in knowing the electric fields over the wells; and if a drop of 1.4 V somewhere in the device is assumed, a much better match can be achieved between the theoretical and experimental shifts. Given this improved match in the shifts the reduction in the oscillator strengths and the broadening are modeled very well. It is concluded that the model is likely to prove a useful tool for optimizing electroabsorption modulator design. >

Electric field control of optical second-harmonic generation in a quantum well

Abstract: We present theoretical predictions of the second‐harmonic susceptibility due to an intersubband transition within the conduction band of a quantum well in an external applied electric field. The asymmetry of the quantum well due to the electric field accounts for the nonvanishing of the second‐order susceptibilities. It is shown that for moderate values of an applied electric field of 10–70 kV/cm, the second‐harmonic susceptibility is generally 10–100 times larger than that of bulk GaAs. Furthermore, this procedure of second‐harmonic generation can be controlled by an external modulating voltage.

Mapping electrodynamic features of the high-latitude ionosphere from localized observations: Combined incoherent-scatter radar and magnetometer measurements for January 18-19, 1984

Abstract: The large-scale electric potential patterns, describing ionospheric convection, are estimated for northern high latitudes during January 18-19, 1984, from combined incoherent-scatter radar and ground magnetometer observations, using the technique of Richmond and Kamide (this issue). The patterns usually have a dominant two-cell characteristic, although the intensities, orientations and shapes of the cells undergo considerable changes with time. Often evident during substorm expansive phases is a “tongue” of low electric potential extending toward the east along the low-latitude edge of the high potential cell at night. Time-series plots of the maximum and minimum electric potentials show that they can respond rapidly to changes in the interplanetary magnetic field Bz component. Total estimated potential drops for this 2-day period range from about 15 kV up to 108 kV. The influence of the different types of data on the resultant estimated electric potential patterns is analyzed. Where available, the direct electric field observations by the radars primarily control the characteristics of the estimated potential patterns, while the magnetometer data have their greatest influence in regions where direct electric field measurements are unavailable. We also employ the statistical electric potential model of Foster et al. (1986) to help fill in the patterns in datasparse regions. For the present study, data coverage is often good enough that the statistical model plays only a secondary role in determining the estimated convection patterns. The ionospheric electrical conductance observations from the Sondrestrom and EISCAT radars are very important in helping modify the statistical conductance model of Fuller-Rowell and Evans (1987) to yield modified conductance distributions suitable for interrelating the electric fields, currents, and magnetic perturbations. Analysis of the statistical uncertainty in the estimated large-scale electric field patterns shows the uncertainty to exceed 50% in the polar cap and sub auroral regions and to be less than 20% only in the vicinity of the radar electric field observations.