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Showing papers on "Electric potential published in 1994"


Journal ArticleDOI
TL;DR: Theoretical analysis of the convergence and the stability of fictitious dynamical methods for electrons shows that a particular damped second-order dynamics has a much faster rate of convergence to the ground state than first-order steepest-descent algorithms while retaining their numerical cost per time step.
Abstract: We study the convergence and the stability of fictitious dynamical methods for electrons. first, we show that a particular damped second-order dynamics has a much faster rate of convergence to the ground state than first-order steepest-descent algorithms while retaining their numerical cost per time step. Our damped dynamics has efficiency comparable to that of conjugate gradient methods in typical electronic minimization problems. Then, we analyze the factors that limit the size of the integration time step in approaches based on plane-wave expansions. The maximum allowed time step is dictated by the highest frequency components of the fictitious electronic dynamics. These can result either from the larger wave vector components of the kinetic energy or from the small wave vector components of the Coulomb potential giving rise to the so called charge sloshing problem. We show how to eliminate large wave vector instabilities by adopting a preconditioning scheme in the context of Car-Parrinello ab initio molecular-dynamics simulations of the ionic motion. We also show how to solve the charge sloshing problem when this is present. We substantiate our theoretical analysis with numerical tests on a number of different silicon and carbon systems having both insulating and metallic character.

139 citations


Journal ArticleDOI
TL;DR: In this article, the stability of an incompressible cylindrical jet carrying surface charge in a tangential electric field, allowing for the finite rate of charge relaxation, is examined, where the viscosity is assumed to be small so that the shear resulting from the tangential surface stress can be large, even for relatively small fields.
Abstract: Many electro-spraying devices raise to a high electric potential a pendant drop of weakly conducting fluid, which may adopt a conical shape from whose apex a thin, charged jet is emitted. Such a jet eventually breaks up into fine droplets, but often displays surprising longevity. This paper examines the stability of an incompressible cylindrical jet carrying surface charge in a tangential electric field, allowing for the finite rate of charge relaxation. The viscosity is assumed to be small so that the shear resulting from the tangential surface stress can be large, even for relatively small fields. This shear can suppress surface tension instabilities, but if too large, it excites electrical ones. For imperfect conductors, surface charge is redistributed by the rapid fluid reaction to variations in tangential stress as well as by conduction. Phase differences between the effects due to the tangential field and the surface charge lead to charge ‘over-relaxation’ instabilities, but the maximum growth rate can still be lower than in the absence of electric effects.

123 citations


Journal ArticleDOI
TL;DR: In this paper, a double-plasmine device was used for investigating the charging of dust grains in a plasma, where single SiC grains were dropped from the top of the device and measured by a sensitive electrometer attached to a Faraday cup on the bottom.
Abstract: An experiment is described for investigating the charging of dust grains in a plasma. The apparatus is a double plasma device into which single dust grains are dropped from the top. The dust charge is detected and measured by a sensitive electrometer attached to a Faraday cup on the bottom. Experiments with electrons from the emissive filaments but without plasma indicate that the grains charge to approximately the filament potential for filament bias voltages smaller in absolute value than /spl minus/70 V. The charge is of order 10/sup 6/ electrons for SiC grains 30-150 /spl mu/m in diameter. At higher bias voltage the charge is reduced due to secondary emission. The charge on grains increases with grain size and is nearly independent of the filament emission current. With plasma in the device, the grains charge both positively and negatively. >

101 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the mechanisms by which radial electric fields are induced in the plasma edge and by which the profile shaping is obtained when radial currents are imposed by electrode polarization.
Abstract: H mode behaviour is usually linked to the existence of radial electric fields or to their shear at the edge of tokamaks. The mechanisms are investigated by which such fields are induced in the plasma edge and by which the profile shaping is obtained when radial currents are imposed by electrode polarization. Earlier detailed experimental field measurements are successfully compared with a theoretical conductivity model in which neoclassical non-ambipolar transport and mobility through ion-neutral collisions are predominant. Strong neoclassical viscosity in the bulk plasma allows significant fields to develop only at the very edge of the plasma. There, a delicate balance between viscosity and ion-neutral friction takes place, which strongly affects the magnitude of the fields and the spatial location and the threshold condition for L-H field bifurcation. It is also shown how to verify experimentally the neoclassical diffusion coefficients in the plateau regime

98 citations


Journal ArticleDOI
TL;DR: In this article, the role of vertical and horizontal electric fields in generating the induced voltage waveform on an overhead wire is analyzed by solving the Telegrapher's equation, in combination with numerical calculations of electric fields from return stroke currents as inducing sources.
Abstract: Lightning-induced voltage waveforms on an overhead wire are analyzed by solving the Telegrapher's equation, in combination with numerical calculations of electric fields from return stroke currents as inducing sources. Based on an equivalent circuit newly developed for an explanation of this method, the roles of the vertical and horizontal electric fields in generating the induced voltage are studied, respectively. By numerical calculations, it is pointed out that the crest value of the lightning-induced voltage waveform at the end of the line is greatly affected by the ground conductivity and the lightning striking points. The accuracy of the computed results is ensured by comparison with the experimental results obtained from a geometrical model on a finitely conducting ground. >

82 citations


Journal ArticleDOI
TL;DR: In this article, the electric field in GaAs surface barrier particle detectors has been simulated to explain the observed reduced charge collection efficiency, using the Poisson and continuity equations, and the electric potential can be calculated numerically in terms of the ionization of deep levels and the spatial variation of the quasi-Fermi-level.
Abstract: We have simulated the electric field in GaAs surface barrier particle detectors in order to explain the observation of reduced charge collection efficiency. Using the Poisson and continuity equations the electric potential can be calculated numerically in terms of the ionization of deep levels and the spatial variation of the quasi-Fermi-level in GaAs. The dependence of the electric field on different parameters (bias voltage, leakage current, material parameters) has been studied and predictions of the simulation have been experimentally verified.

69 citations


Journal ArticleDOI
TL;DR: The present model accounts qualitatively for the dependence of total potential and ion distribution on number of ions and pseudopotential and increases ion density near the center of the trap without widening the ion spatial distribution.

63 citations


Journal ArticleDOI
TL;DR: Findings indicate that Na,K-ATPase can recognize an electric signal, either regularly oscillatory or randomly fluctuating, for energy coupling, with high fidelity and indicate that the ECC is a plausible mechanism for the recognition and processing of electric signals by proteins of the cell membrane.

62 citations


Journal ArticleDOI
TL;DR: In this paper, a special case of Radon transform is used to recover the electric field distribution from measurements of light phase shifts, where the applied electric field direction changes along the light path and the light polarization equations are generalized.
Abstract: Electric field distributions measured using the Kerr effect cause a phase shift between light components polarized parallel and perpendicular to the electric field, proportional to the magnitude squared of the electric field components in the plane perpendicular to light propagation integrated over the light path length. One wishes to recover the electric field distribution from measurements of light phase shifts. For axisymmetric geometries where the electric field depends only on the radial coordinate and whose direction is constant along the light path, as is the case along a planar electrode, the total phase shift for light propagating at a constant distance from the center of symmetry and the electric field distribution are related by an Abel transform pair, a special case of Radon transforms typically used in image reconstructions with medical tomography and holography. The more general Radon transform relates the optical phase shift to non-axisymmetric electric field distributions but is restricted to cases where the applied electric field is perpendicular to the plane of light propagation. If the applied electric field direction changes along the light path, it becomes necessary to account for the change in direction of the light components parallel and perpendicular to the applied electric field and the light polarization equations are generalized. >

55 citations


Journal ArticleDOI
TL;DR: In this article, the effect of an electric field on the self-propagation reaction between silicon and carbon to synthesize β-SiC was investigated, and it was shown that in the absence of a field at a threshold level, no self-sustaining reaction was observed and as the applied voltage increases, a linear increase in the velocity of the reaction wave was observed.
Abstract: We report on the effect of an electric field on the self‐propagating reaction between silicon and carbon to synthesize β‐SiC. In the absence of a field at a threshold level, no self‐sustaining reaction is observed, and as the applied voltage increases, a linear increase in the velocity of the reaction wave is observed. This first demonstration of the effect of fields on such reactions is explained in terms of a model in which the role of the field is confined to the reaction zone.

55 citations


Journal ArticleDOI
TL;DR: In this article, a modified charge simulation method for calculating the electric potential and field distribution along AC HV outdoor insulators is presented, and the salient feature of this method is the significantly smaller number of unknowns and the corresponding reduction in computational complexity when compared to earlier charge simulation methods.
Abstract: A modified charge simulation method for calculating the electric potential and field distribution along AC HV outdoor insulators is presented. The salient feature of this method is the significantly smaller number of unknowns and the corresponding reduction in computational complexity when compared to earlier charge simulation methods. Non-ceramic and ceramic suspension insulators of voltage ratings ranging from 115 to 500 kV, and non-ceramic line posts (115 and 230 kV) have been modeled under clean and dry surface conditions. Good agreement is obtained between the present calculations and measured data, calculated values using other numerical techniques and observations from service experience, which demonstrates the practical viability of the technique. >

Book
29 Aug 1994
TL;DR: The Interactions of Electric Charges and Fields in Electric Circuits as mentioned in this paper The Interaction of Electric charges in Matter and Magnetic Fields in Matter, and Magnetic Field of Distributed Charges.
Abstract: The Interactions of Electric Charges. Charges in Matter. Electric Field. The Electric Field of Distributed Charges. Electric Currents. Charges and Fields in Electric Circuits. Capacitors in Circuits. Electric Potential. Potential and Circuits. Gauss's Law. Magnetic Field. Magnetic Force. Magnetic Induction. Electromagnetic Radiation. Index.

Journal ArticleDOI
TL;DR: In this paper, the authors show that there is a significant relationship between magnetic activity and the high-latitude ionospheric convection electric fields, and that the substorm differences are detected primarily near midnight, where there is an enhanced westward electric field associated with a penetration of the positive potential, dawn convection cell into the negative, dusk convection cells.
Abstract: In this paper we show that there is a significant relationship between magnetic activity and the high-latitude ionospheric convection electric fields. In particular, when the westward electrojet is much stronger than the eastward electrojet, as occurs during magnetospheric substorms, the electric field patterns show subtle, but important, changes from the configurations that are obtained under more quiet conditions. The substorm differences are detected primarily near midnight, where there is an enhanced westward electric field associated with a penetration of the positive-potential, dawn convection cell into the negative, dusk convection cell. The peak value of the positive potential also increases during substorms and its location shifts closer to midnight, while the negative cell remains relatively constant. These results were obtained through the use of a procedure that uses electric field measurements from the DE 2 satellite to derive maps of the locations of the convection reversal boundaries, and functions for the distribution of the electric potential around these boundaries. This was accomplished for several sets of data that were grouped according to the interplanetary magnetic field and geomagnetic activity. Further refinements in our analysis procedure are possible. The results could be used to produce more accurate maps of ionospheric convection. We also show that distortions of the electric field patterns near midnight are simply the result of polarization electric fields around conductivity enhancements. The distorted electric fields satisfy the condition that the ionospheric Hall current be divergence-free.


Journal ArticleDOI
01 Jun 1994-Wear
TL;DR: In this paper, a nematic liquid crystal was used as the lubricant and electric fields were applied across the liquid crystal film to control friction coefficients under boundary lubrication regime with a steel-to-steel contact.

Journal ArticleDOI
A. Bergmann1
TL;DR: In this article, two-dimensional particle simulations of the sheath in front of a flat Langmuir probe mounted into a particle absorbing plate are performed to study the influence of a strong magnetic field (relation between Larmor radii and Debye length: ρe≤λD, ρi≫λD) oriented obliquely to the probe surface.
Abstract: Two‐dimensional particle simulations of the sheath in front of a flat Langmuir probe mounted into a particle absorbing plate are performed to study the influence of a strong magnetic field (relation between Larmor radii and Debye length: ρe≤λD, ρi≫λD) which is oriented obliquely to the probe surface. Ion‐attracting probes are considered and the sheath is assumed to be collisionless. The full particle orbits in the homogeneous magnetic field and the self‐consistent electric potential are calculated with a particle‐in‐cell (PIC) code with two spatial coordinates and three velocity components (2d,3v). The main results are: In the sheath the ion trajectories are bent towards the normal to the probe surface so that the ion flow is focused to the edges of the probe. This leads to an enhancement of the ion current as compared to the current flowing in the flux tube subtended by the probe. As a consequence the current does not saturate at large (negative) probe voltage, because the thickness of the Debye sheath, and thus the effective probe size, grows with increasing probe voltage. This effect is particularly strong if the sheath thickness is about as large, or larger than, the projection of the probe size along the magnetic field lines. These results can help to explain the ion‐current nonsaturation found in recent measurements with Langmuir probes in the boundary layer of magnetically confined plasmas.

Journal ArticleDOI
TL;DR: The present numerical model can be extended to general cases with any volume conductor shape or with any distribution or orientation of the current dipoles, allowing simulation with considerably larger meshes.

Journal ArticleDOI
TL;DR: In this paper, a method for visualization and quantification of the latent electric charge image on dielectric materials has been developed using Pockels effect of a BSO (Bi12SiO20) single crystal, a charge coupled device camera recording system, and a computer image processing technique.
Abstract: Techniques for visualization and quantification of the latent electric charge image on dielectric materials have been developed using Pockels effect of a BSO (Bi12SiO20) single crystal, a charge coupled device camera recording system, and a computer image processing technique. The Pockels device of the BSO single crystal was used as a transducer to transfer the surface charge density to retard the transmitted light beam. The basic principle of advanced electro‐optical surface charge measurement is described and typical surface charge distributions of positive and negative discharge streamers produced by an ac (50 Hz) high voltage are demonstrated. The measured surface charge images are shown on a computer monitor as three‐dimensional figures.

Journal ArticleDOI
TL;DR: A potential function method for three-dimensional asymmetric problems of piezoiher-moelasticity of hexagonal materials of crystal class 6 mm in cylindrical coordinates is proposed in this article.
Abstract: A potential function method for three-dimensional asymmetric problems of piezoiher-moelasticity of hexagonal materials of crystal class 6 mm in cylindrical coordinates is proposed. The method employs two piezothermoelaslic potential functions, four piezoelastic potential functions, and a piezoelectric potential function. One of the piezother-moelastic potentials and the four piezoelastic potential functions are governed by simple uncoupled differential equations, which are derived from the stress equations of equilibrium and the equation of electrostatics. The remaining piezothermoelastic function and the piezoelectric potential function are expressed in terms of the previously obtained piezothermoelastic function. As an illustrative example, the problem of an infinite, thin piezothermoelastic plate subjected to axisymmetric surface heating is analyzed. Numerical results are obtained for the stresses and the electric potential in a cadmium selenide plate. The thermally induced stress distributions are com...

Journal ArticleDOI
TL;DR: In this article, the T/sub 0/spl Omega/ formulation was used to model a 100 MVA power transformer short circuit test in the transient state and the same device was studied at no-load.
Abstract: Most of the electromagnetic devices work connected to an electric circuit and their numerical simulation in 3D leads to a large number of unknowns. To deal with these problems we propose to use the T/sub 0//spl Omega/ formulation and describe the way of coupling magnetic and electric circuit equations. The coupling is obtained by expressing the electric vector potential T/sub 0/ from the current and the flux of induction and from the magnetic scalar potential /spl Omega/. To consider the magnetic nonlinearity we use the Newton-Raphson procedure. This formulation is used to model a 100 MVA power transformer short circuit test in the transient state. The same device is studied at no-load. >

Journal ArticleDOI
TL;DR: In this article, the authors used Coulomb's law to estimate the electric field in a 3D domain, where point charges were placed in a 200 × 200 × 100 m grid.
Abstract: Charge distributions were modeled in a three-dimensional domain, 10 km on each side, by placing point charges in a 200 × 200 × 100 m grid. Charge locations were based on electric field soundings and the one-dimensional approximation to Gauss's law. The model calculates the electric field due to all the point charges and their corresponding image charges using Coulomb's law. Vertical electric fields from the model are not significantly different from the observed fields and are also nearly identical to fields resulting from infinitely extensive charge layers. These findings show that Gauss's law in one dimension is a valid method for approximating the charge density of finite layers. The model vertical electric fields are almost equivalent for charge regions that are reduced in x and y dimensions from 10 km to 6 km. Thus, extending charge layers for as little as 3 km on either side of the sounding location sufficiently reproduces the entire field when typical, observed charge densities are used. For a vertical path 1 km from the edge of the 10 × 10 km model domain, the calculated vertical electric field is reduced by less than 10% from its value through the center of the domain. This finding means that the observed electric field profile can be far from the center of the charge layers and still allow a good approximation of the their charge densities and depths. Relatively large changes (factor of about 5) in charge density over relatively short (less than about 2 km) horizontal distances are needed to produce observed magnitudes of horizontal electric fields.

Journal ArticleDOI
TL;DR: In this article, the critical axial electric field needed to hold a nonconducting liquid bridge of given slenderness was determined using the Plateau tank technique, which is used to minimize gravity forces on earth.
Abstract: Experimental determination of the critical axial electric field needed to hold a nonconducting liquid bridge of given slenderness is presented. The Plateau tank technique is used to minimize gravity forces on earth. Improvement of previous data is achieved by determining the gravitational Bond number. The results are compared to numerical calculations of the stability limits, showing a good agreement.

Journal ArticleDOI
TL;DR: In this article, the trajectroy of the Dynamics Explorer 2 (DE 2) satellite over the auroral emissions is determined from nearly simultaneous observations with the imager on the DE 1 satellite at a higher altitude.
Abstract: Measurements have been made of electric and magnetic fields, plasma drifts, and electron precipatation within a surge at the westward, leading edge of the auroral 'bulge' at the peak of the substorm expansion phase. The trajectroy of the Dynamics Explorer 2 (DE 2) satellite over the auroral emissions is determined from nearly simultaneous observations with the imager on the DE 1 satellite at a higher altitude. The electric field and plasma drift measurements have enabled us to deduce the basic configuration of the ionospheric electric potential, or plasma convection, around the surge. The electric potential shows that the bulge is associated with a protrusion of the dawn convection cell into the dusk cell, poleward of the 'Harang discontinity.' This protrusion conains a westward electric field that strongly enhances the westard electrojet current by the creation of a "Cowling channel.' This westward electric field, and the associated Cowling current, appear to terminate within the surge, which contains an intense, upward field-aligned current. The magneitc field measurements show that the region containing this field-aligned current is shaped more like a cylinger rather than a long sheet. The total is found to exceed one-half million amperes.

Journal ArticleDOI
TL;DR: In this article, a nonlocal density-functional theory of inhomogeneous ionic fluids is extended to study the structure of electric double layer for a charge-asymmetric (2:1) situation involving hard sphere ions of equal diameter with a continuum or neutral hard sphere model for the solvent.
Abstract: A nonlocal density‐functional theory of inhomogeneous ionic fluids proposed by us recently [J. Chem. Phys. 100, 5219 (1994)] for symmetric electrolytes is extended to study the structure of electric double layer for a charge‐asymmetric (2:1) situation involving hard sphere ions of equal diameter with a continuum or neutral hard sphere model for the solvent. The hard sphere contributions to the excess free energy density and its derivatives for the inhomogeneous system are evaluated nonperturbatively through a position‐dependent effective weighted density, which is also used to obtain the corresponding ionic contributions through a second‐order functional Taylor expansion. The calculated results for the continuum solvent model show reasonably good agreement with the available simulation results, while the layering effect due to hard sphere exclusion and the charge inversion phenomena are some of the interesting consequences arising from the molecular nature of the solvent.

Proceedings ArticleDOI
05 Jun 1994
TL;DR: In this article, the accumulation of space charge in solid dielectrics was examined from the macroscopic point of view using electromagnetic field theory, and it was shown that the occurrence of such charges is an inherent consequence of a non-uniform conductivity.
Abstract: The accumulation of space charge in solid dielectrics is examined from the macroscopic point of view using electromagnetic field theory. For practical dielectrics, it is shown that the occurrence of such charges is an inherent consequence of a non-uniform conductivity. The influence of both temperature and electric field strength upon this space charge formation is elucidated. Thereafter the theory is applied to DC cables. >

Journal ArticleDOI
TL;DR: In this paper, the authors presented the first Fourier transform ion cyclotron resonance (FT-ICR) ion trap designed to produce both a linear spatial variation of the excitation electric potential field and a linear response of the detection circuit to the motion of the confined ions.

Journal ArticleDOI
TL;DR: In this article, the authors proposed an antistatic neutralization method for static electricity by soft X-ray radiation and vacuum UV radiation, which can completely reduce electrostatic potential to 0V within a short time.

Journal ArticleDOI
TL;DR: In this article, a method of potential functions introduced successively to integrate the field equations of three-dimensional problems for transversely isotropic piezoelectric materials was used to obtain the so-called general solution in which the displacement components and electric potential functions are represented by a singular function satisfying some special partial differential equations of 6th order.
Abstract: Using a method of potential functions introduced successively to integrate the field equations of three-dimensional problems for transversely isotropic piezoelectric materials, we obtain the so-called general solution in which the displacement components and electric potential functions are represented by a singular function satisfying some special partial differential equations of 6th order. In order to analyse the mechanical-electric coupling behaviour of penny-shaped crack for above materials, another form of the general solution is obtained under cylindrical coordinate system by introducing three quasi-harmonic functions into the general equations obtained above. It is shown that both the two forms of the general solutions are complete. Furthermore, the mechanical-electric coupling behaviour of penny-shaped crack in transversely isotropic piezoelectric media is analysed under axisymmetric tensile loading case, and the crack-tip stress field and electric displacement field are obtained. The results show that the stress and the electric displacement components near the crack tip have (r−1/2) singularity.

Journal ArticleDOI
TL;DR: In this paper, the electric potential distribution across a Nafion® membrane during water electrolysis using a solid polymer electrolyte has been computed and the use of a membrane strip to measure separately the anodic and cathodic overvoltages is discussed.

Journal ArticleDOI
TL;DR: In this paper, the electric and magnetic fields of a point charge moving with constant velocity are derived from retarded integrals representing solutions of Maxwell's equations for electric and magnetic fields of arbitrary time-dependent charge and current distributions.
Abstract: Equations for the electric and magnetic fields of a point charge moving with constant velocity are derived from retarded integrals representing solutions of Maxwell’s equations for electric and magnetic fields of arbitrary time‐dependent charge and current distributions. In contrast to conventional derivations, the derivations presented here are based exclusively on general electromagnetic field equations and do not make use of retarded potentials or relativistic equations. The derivations lead to some notable conclusions concerning the electric and magnetic fields of an arbitrary charge distribution moving with constant velocity.