Showing papers on "Electric field published in 1987"

Empirical high-latitude electric field models

Abstract: The present analysis of electric field measurements from the Dynamics Explorer 2 satellite, which extends previous empirical models, emcompasses much data from polar crossings entering and exiting the high latitudes in all magnetic local time zones. The goal is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns. Significant large-scale revisions of the OGO 6 dawn-dusk measurement models are made. The deformations of the two-cell patterns lead to sunward convection in dayside polar regions, while maintaining the integrity of the nightside convection pattern.

The two-dimensional Coulomb gas, vortex unbinding, and superfluid-superconducting films

Abstract: The article reviews the two-dimensional Coulomb gas model and its connection to vortex fluctuations for a two-dimensional superfluid. The neutral and non-neutral versions of the Coulomb gas are discussed and the relation to an equivalent sine-Gordon field theory is given. The charge-unbinding picture is used to elucidate some essential properties of the Coulomb gas. Derivations of approximate renormalization equations are sketched and the phase transition for the neutral two-dimensional Coulomb gas is described. The Kosterlitz renormalization-group equations are reviewed in some detail. The vortex-Coulomb gas charge analogy is carefully explained. The connections between experiments for $^{4}\mathrm{He}$ films and superconducting films and the neutral and non-neutral versions of the Coulomb gas are outlined using concepts like the universal jump and the Coulomb gas scaling relations. The properties of a dynamical version of the Coulomb gas, corresponding to vortex dynamics, are discussed and related to experiments. An analogy with Maxwell's equations in two dimensions is also given.

Calculation of linear and nonlinear intersubband optical absorptions in a quantum well model with an applied electric field

Abstract: Analytic forms of the linear and the third-order nonlinear optical intersubband absorption coefficients are obtained for general asymmetric quantum well systems using the density matrix formalism, taking into account the intrasubband relaxation. Based on this model, we calculate the electric field dependence of the linear and the third-order nonlinear intersubband optical absorption coefficients of a semiconductor quantum well. The energy of the peak optical intersubband absorption is around 100 meV (wavelength is 12.4 μm). Thus, electrooptical modulators and photodetectors in the infrared regime can be built based on the physical mechanisms discussed here. The contributors to the nonlinear absorption coefficient due to the electric field include 1) the matrix element variation and 2) the energy shifts. Numerical results are illustrated.

Electrostatics, Principles, Problems and Applications

Abstract: Historical background and elementary theory: Historical background Fundamental definitions Orders of magnitude Summary of electrostatic equations in uniform fields Gauss's law - the electric field due to an assembly of charges Electrification of solids and liquids: Contact and frictional charging Corona charging Charging by capture of small particles Induction charging Double-layer charging References Measurements and instrumentation: Introduction Potential dividers and resistance probes Electrometers and electrostatic voltmeters Field meters and non-contacting voltmeters Charge measurement - the Faraday cup Measurement of the charge and mobility of individual particles Field and potential probes The use of the Kerr and Pockels effect for measurement of electric fields Capacitance meters Measurement of resistance and resistivity Energy of electrostatic sparks Electrostatics in gas filtration: Introduction Electrostatic precipitation Electron beam desulphurisation and denitrisation Electrostatically enhanced cyclone separators Electrostatic scrubbers and granular bed filters Electrostatically enhanced fabric filters Appendix Miscellaneous applications: Electrostatic atomisation Electrostatic spray coating Electrostatic separation Electrokinetic phenomena in liquids Dielectrophoresis Applications of the corona discharge Electrodynamic containment and control of particles Applications of electromechanical forces Electrostatic copying Electrostatics and the textile industry Electrostatic crystals Electrostatic generators Hazards and problems: Fire and explosion hazards Electrostatic sparks Non-electrostatic sparks Electrostratic eliminators Antistatic agents Electrostatic problems in the electronics industry Adhesion Appendix Theory: Fundamental laws of electrostatics Capacitance and capacitors Polarisation Identification of field lines and equipotentials Electric field and potential by solution of Laplace's equation Earnshaw's theorem Corona discharge theory Appendix Index

Observation of Stark shifts in quantum well intersubband transitions

Abstract: We have observed Stark shifts of quantum well intersubband transitions in a perpendicular electric field. Two samples consisting of 100 and 120 A GaAs quantum wells separated by 350 A AlGaAs barriers showed optical absorption peaks at 11.1 and 13.9 μm, respectively. In an electric field of 36 kV/cm, the 13.9 μm peak shifted to 13.7 μm and the 11.1 μm shifted to 11.0 μm, in good agreement with theoretical calculations. These tunable transitions can be applied to high‐speed infrared light modulators.

Investigations into the mechanisms of electrohydrodynamic spraying of liquids

Abstract: The mechanism of stable jet formation was investigated by observing the motion of the liquid in a jet close to the capillary tip from which it emerges under the influence of an electric field. Tracer particles of lycopodium were inserted in the liquid and streak photographs were taken of a stable jet formed under the application of 10.5 kV and a flow rate of 30 ml/h. These photographs show an axisymmetric circulation of the liquid in the conical base of the jet, invalidating previous theories that have assumed a uniform velocity profile in the liquid cone. This axisymmetric motion of the liquid in the jet was explained in terms of interfacial electrical shear stresses. Due to the semi-insulating nature of the liquid, there will exist a potential difference between the base of the capillary and the tip of the cone. This potential drop ensures that the interface is subjected to a tangential electric field in the direction of flow and hence an electric shear stress on the surface of the cone. Both tangential and normal fields on the cone were calculated from a knowledge of the jet profile and current. The tangential field on the surface of the cone was calculated by considering it to be a section of a sphere and dividing it into five sections. Each section was assumed to form an equipotential surface normal to the direction of flow and to have a constant current flowing through it. The normal field was calculated numerically using a computer program that estimates the potential distribution within a region subject to given boundary conditions using the finite element method. The results of calculation showed that the shear force acting on the cone was about 5 to 10 times smaller than the normal force. However, the normal force was found to be fairly constant and independent of applied voltage, within the range studied. In contrast, the shear force showed a tendency to decrease with an increase in applied voltage. It was also observed that as the voltage was increased, the length of the jet decreased. This could be explained in terms of the reduction of tangential shear force with an increase in applied voltage, thus reducing jet stability.

Effect of closed classical orbits on quantum spectra: Ionization of atoms in a magnetic field.

Abstract: Measurements of the absorption spectrum near the ionization threshold for an atom in a strong magnetic field showed that the spectrum is a superposition of many oscillatory terms (``quasi-Landau oscillations''). We have developed a quantitative theory which shows that each classical closed electron orbit which begins and ends near the nucleus contributes an oscillatory term to the average oscillator strength. The theory gives new understanding of the behavior under combined Coulomb and Lorentz forces, and it elucidates the roles of isolated closed orbits in chaotic systems. The first results of this theory are shown to be in good agreement with experimental results.

A study of photon emission from n-channel MOSFET's

Abstract: It is known that an n-channel MOSFET, operating in the saturation region, is accompanied by visible light emission. The spectral distribution of this emitted light is reported in this paper for the first time. It behaves as exp (-α . hv) under various bias conditions (α: constant); the energy state of hot electrons is described as a Maxwell-Boltzmann distribution. The hot-electron temperature in an n-channel MOSFET is experimentally evaluated from the photon spectrum analysis. As compared with the electric field strength calculated by two-dimensional simulation, the hot-electron temperature is found to be determined as a function of the electric field strength in the drain avalanche region.

Intersubband optical absorption in a quantum well with an applied electric field.

Abstract: We present new results for the electric field dependence of the intersubband optical absorption within the conduction band of a quantum well. We show that for increasing electric field the absorption peak corresponding to the transition of states 1\ensuremath{\rightarrow}2 is shifted higher in energy and the peak amplitude is increased. These features are different from those of the exciton absorption. It is also found that the transition 1\ensuremath{\rightarrow}3, forbidden when F=0, is possible when F is nonzero.

Mechanistic approaches to interactions of electric and electromagnetic fields with living systems

Abstract: Ions and Membrane Surfaces.- Ionic Processes at Membrane Surfaces: The Role of Electrical Double Layers in Electrically Stimulated Ion Transport.- Membrane Transduction of Low Energy Level Fields and the Ca++ Hypothesis.- Electrochemical Kinetics at the Cell Membrane: A Physicochemical Link for Electromagnetic Bioeffects.- Modification of Charge Distribution at Boundaries between Electrically Dissimilar Media.- The Role of the Magnetic Field in the EM Interaction with Ligand Binding.- Cyclotron Resonance in Cell Membranes: The Theory of the Mechanism.- Experimental Evidence for Ion Cyclotron Resonance Mediation of Membrane Transport.- Frequency and Amplitude Dependence of Electric Field Interactions: Electrokinetics and Biosynthesis.- Macromolecules.- The Influence of Surface Charge on Oligomeric Reactions as a Basis for Channel Dynamics.- Internal Electric Fields Generated by Surface Charges and Induced by Visible Light in Bacteriorhodopsin Membranes.- Interaction of Membrane Proteins with Static and Dynamic Electric Fields via Electroconformational Coupling.- Interactions Between Enzyme Catalysis and Non Stationary Electric Fields.- Patterns of Transcription and Translation in Cells Exposed to EM Fields: A Review.- Interaction of Electromagnetic Fields with Genetic Information.- Membrane Matrix.- Transient Aqueous Pores: A Mechanism for Coupling Electric Fields to Bilayer and Cell Membranes.- Electrorotation - The Spin of Cells in Rotating High Frequency Electric Fields.- Membranes, Electromagnetic Fields and Critical Phenomena.- Field Effects in Experimental Bilayer Lipid Membranes and Biomembranes.- Fusogenic Membrane Alterations Induced by Electric Field Pulses.- Integrated Systems.- Some Possible Limits on the Minimum Electrical Signals of Biological Significance.- Electrostatic Fields and their Influence on Surface Structure, Shape and Deformation of Red Blood Cells.- Cell Surface Ionic Phenomena in Transmembrane Signaling to Intracellular Enzyme Systems.- Low Energy Time Varying Electromagnetic Field Interactions with Cellular Control Mechanisms.- The Mechanism of Faradic Stimulation of Osteogenesis.- The Role of Calcium Ions in the Electrically Stimulated Neurite Formation in Vitro.- On the Responsiveness of Elasmobranch Fishes to Weak Electric Fields.- Contributors.

Frequency dependence of electric field modulation of fibroblast protein synthesis

Abstract: The effect of electric current on protein biosynthesis in mammalian fibroblasts was investigated with neonatal bovine fibroblast-populated collagen matrices. The field strength dependence of electric field modulation of proline incorporation into extracellular and intracellular protein was measured over a frequency range from 0.1 to 1000 hertz. A frequency- and amplitude-dependent reduction in the rate of incorporation was observed. In tissues containing cells aligned either parallel or perpendicular to the electric field, this response was dependent on the orientation of the cells relative to the direction of the applied electric field. This study demonstrates that currents of physiological strength can stimulate alterations in biosynthesis and thereby may influence tissue growth, remodeling, and repair.

Fluid model simulations of a 13.56‐MHz rf discharge: Time and space dependence of rates of electron impact excitation

Abstract: Results from fluid model simulations of a 13.56‐MHz rf discharge qualitatively reproduce many of the experimentally observed features of time and space resolved electron impact excitation in several gases (oxygen, nitrogen, and silane). The shape of the excitation rate waveform, its direction of propagation, time of occurrence in the rf period, and the initial increase in intensity followed by attenuation are all observed experimentally as well as in the simulation. Secondary electrons play no direct role in the excitation waveform in the simulation, although secondary electron creation is included in the model. The excitation waveform is the result of the combination of electron motion, electric field profiles, and the electron energy balance in the discharge. Electron heating by the rf field peaks at the plasma‐sheath boundary, resulting in a local rise in electron mean energy there. It is suggested that this electron heating mechanism is common to all high‐frequency rf discharges in electropositive or ...

Electromechanical stresses produced in the plasma membranes of suspended cells by applied electric fields.

Abstract: We analyze the electrical and mechanical stress in the bounding membrane of a cell (or vesicle) in suspension which is deformed by an external applied field. The membrane is treated as a thin, elastic, initially spherical, dielectric shell and the analysis is valid for frequencies less than the reciprocal of the charging time (i.e. less than MHz), or for constant fields. A complete analytic solution is obtained, and expressions are given which relate the deformation, the surface tension and the transmembrane potential difference to the applied field. We show that mechanical tensions in the range which lyse membranes are induced at values of the external field which are of the same order as those which are reported to lyse the plasma membranes of cells in suspension.

Self‐consistent study of a perpendicular collisionless and nonresistive shock

Abstract: Particle dynamics and field behavior associated with a perpendicular collisionless supercritical and viscous shock are investigated by use of numerical simulation. A one‐dimensional, relativistic, fully electromagnetic and nonperiodic particle simulation code (for both electrons and ions) is used where self‐consistent space‐charge effects and induced effects are totally included. The principal field patterns of the shock (trailing wave train, ramp, and foot region) are studied in detail and are shown to have scale lengths mainly dictated by ion dynamics; the behavior of the corresponding plasma currents associated with the different field components is also presented. Ions are shown to suffer successive ‘‘acceleration–trapping–detrapping’’ at the shock front, and locally in the trailing wave train of the downstream region through combined effects of the electrostatic and magnetic fields. While detrapped, the reflected ions describe very large Larmor orbits and cause a ring distribution; a large rapid nonstochastic ion heating results from this ion gyration. This heating (resistivity‐free) is the main source of dissipation and is responsible for large field damping. Competitive effects such as particle stochasticity, particle trapping, wave damping, wave overtaking, and dispersion effects are shown to interact with each other and to affect the overall dissipation mechanism. Comparison with previous works is also discussed. Various Mach number situations are considered, leading to the definition of a transitory regime between subcritical and supercritical regimes and of a corresponding critical threshold of the electrostatic field. In contrast with the supercritical regime, the subcritical regime is characterized by a low density of trapped‐reflected ions, a broad ion distribution function with a weak tail, and a weak adiabatic bulk ion heating.

Measurements of Nonlinear Dielectricity in Ferroelectric Polymers

Abstract: Experimental procedures and exemplifying results are described in relation to a nonlinear dielectric investigation of ferroelectric polymers. The apparatus developed here was used to apply a sinusoidal electric field and to detect fundamental and higher harmonic electric displacements with a 0.01% accuracy by means of digital sampling and Fourier transform techniques. Three types of experiments were made for PVDF. Measurements at relatively low fields determined the nonlinear dielectric constants in that the second-order constant was shown to reflect the polarity of the sample and the third order one was positive being consistent with cooperative dipoles. The ferroelectric hysteresis loops obtained at very high fields were analyzed in terms of the higher-order Fourier coefficients. The use of a double frequency wave determined the field-dependent linear dielectric constants which showed a maximum during polarization reversal.

The Current-Voltage Relationship in Auroral Current Sheets.

Abstract: The current-voltage relation within narrow auroral current sheets is examined through the use of high-resolution data from the high-altitude Dynamics Explorer 1 satellite. The north-south perpendicular electric field and the east-west magnetic field are shown for three cases in which there are large amplitude, oppositely directed paired electric fields which are confined to a region less than 20 km wide. The magnetic field variations are found to be proportional to the second integral of the high-altitude perpendicular electric field. It is shown that at the small-scale limit, this relationship between ΔB and E is consistent with a linear “Ohm's law” relationship between the current density and the parallel potential drop along the magnetic field line. This linear relationship had previously been verified for large-scale auroral formations greater than 20 km wide at the ionosphere. The evidence shown here extends our knowledge down to the scale size of discrete auroral arcs.

An Isotropic Electric-Field Probe with Tapered Resistive Dipoles for Broad-Band Use, 100 kHz to 18 GHz

Abstract: A new broad-band electric-field probe, capable of accurately characterizing and quantifying electromagnetic (EM) fields, has been developed at the National Bureau of Standards (NBS). The probe's 8-mm resistively tapered dipole elements allow measurement of eleetric fields between 1 and 1600 V/m from 1 MHz to 15 GHz, with a flatness of +-2 dB. A mutually orthogonal dipole configuration provides an overall standard deviation in isotropic response, with respect to angle, that is within +-0.3 dB. Both the theoretical and developmental aspects of this prototype electric-field probe are discussed in this paper.

Nonsteady boundary layer flow including ionospheric drag and parallel electric fields

Abstract: A simple two-dimensional model is developed for the perpendicular flow dynamics of boundary layers located on closed magnetic field lines in the equatorial magnetosphere. In addition to viscous damping in the equatorial region, nonlocal dissipation associated with the closure of field-aligned currents in the ionosphere and field-aligned potential drops is included and is shown to have two consequences: (1) coupling to the ionosphere causes large-scale disturbances to decay anisotropically and (2) field-aligned potential drops promote long-lived fluctuations at scale lengths that can be comparable to the inverted V scale but which vary with the local Hartmann number (a measure of the ratio of ionospheric resistive friction to magnetospheric viscous friction). Depending on the degree of anisotropy, the combined effect is a tendency for the two-dimensional flow to organize into either relatively isotropic eddies or essentially one-dimensional flow to organize into either relatively isotropic eddies or essentially one-dimensional striations. The limiting case of a one-dimensional flow is considered with applications to the low-latitude boundary layer and internal magnetospheric shear layers. A particular boundary layer equilibrium state is compared with observations of an ionospheric boundary layer region and is found to be in fair agreement with the observed properties for reasonable valuesmore » of the model parameters. It is also shown, under certain conditions, that a monotonically varying internal shear layer can form paired oscillations in the electric field, which are characteristic of the so-called V shocks that occur in and above the auroral acceleration region.« less

A Very Stable Calculation Method for Ion Flow Field of HVDC Transmission Lines

Abstract: This paper describes a new, stable method of calculating ion flow fields in the presence of wind. The principle of the new method is to use the integral form of the current continuity equation instead of Poisson's equation for computing space potential. It has been demonstrated that this new method can give consistent results for any high boundary value. The calculated profiles of electric field and ion current density on the ground have been compared and discussed with the measured ones for the artificial wind conditions under very high current density and the UHV DC test transmission line.

Electrical conduction of purified cyclohexane in a divergent electric field

Abstract: The mechanisms of field emission and field ionisation are indeed operative but with very drastic conditions i.e., highly purified liquid and very sharp tips.

Lipid swelling and liposome formation on solid surfaces in external electric fields

Abstract: External electric fields can induce or prevent lipid swelling and liposome forma- tion on solid surfaces. These effects depend on the type of the lipid and the surface, the medium parameters (temperature, osmolarity, ionic strength), the dried lipidlayer thick- ness, the type and parameters of the electric field (direct current (DC) or alternating cur- rent (AC), amplitude, frequency, current), the place of the lipid (on the electrode surface itself or on another surface) and the time of exposure. This paper reviews experimental results and theoretical estimates for these effects and presents new data and estimates for the effects of lipid charge and frequency of the field. The basic conclusion is that the electr- ic fields can affect lipid swelling and liposome formation by at least four mechnisms: (1) direct electrostatic interaction, (2) redistribution of the double layer counter-ions, (3) membrane surface and line tension changes and (4) electroosmotic effects.

Method for remotely detecting an electric field using a liquid crystal device

Abstract: A method for detecting an electric field surrounding an electrical component with a device having a liquid crystal display element, the device being positioned at a distance from the component and being unconnected ohmically to either the component or ground.

Magnetic elliptical polarization of Schumann resonances

Abstract: Measurements of orthogonal, horizontal components of the magnetic field in the ELF range obtained during September 1985 show that the Schumann resonance eigenfrequencies determined separately for the north-south and east-west magnetic components differ by as much as 0.5 Hz, suggesting that the underlying magnetic signal is not linearly polarized at such times. The high degree of magnetic ellipticity found suggests that the side multiplets of the Schumann resonances corresponding to azimuthally inhomogeneous normal modes are strongly excited in the highly asymmetric earth-ionosphere cavity. The dominant sense of polarization over the measurement passband is found to be right-handed during local daylight hours, and to be left-handed during local nighttime hours.

Modeling of corona characteristics in a wire-duct precipitator using the charge simulation technique

Abstract: The charge simulation technique has been adapted to model the electrostatic and the corona characteristics in clean air of a duct-type electrostatic precipitator. The study involves the evaluation of the electric potential, electric field, and charge density in the interelectrode space as a function of corona current. The results show good agreement with published experimental data. The method developed can be applied to other geometries in the presence of space charge. The commonly used assumption that the space charge affects the magnitude but not the direction of the electric field is shown to be inadequate for large values of corona current. Also, the effect of using different values for the mobility of negative ions is presented.

Transient orientation of linear DNA molecules during pulsed-field gel electrophoresis

Abstract: The transient orientation of lambda DNA and lambda-DNA oligomers has been measured during pulsed field gel electrophoresis. The DNA becomes substantially aligned parallel to the electric field E. In response to a single rectangular pulse, orientation shows an overshoot with a peak at 1 second, then a small undershoot, and finally a plateau. When the field is turned off, the orientation dissipates in two distinct exponential phases. Field inversion leads to periods of orientation with intervening periods of reduced orientation as the chains reverse direction. Field inversion pulses applied to linear oligomers of lambda-DNA show that orientation responses slow down but increase in amplitude as molecular weight increases, for a given field. Because DNA stretching and alignment parallel to E are expected to correlate with DNA velocity, the velocity in response to a pulsed field is also expected to exhibit an overshoot.

Spectral studies of the sources of ionospheric electric fields

Abstract: Spectral analyses (applying the Fourier analysis methods) were performed on three incoherent scatter radar data sets (obtained at Jicamarca, Peru; Chatanika, Alaska; and Arecibo, Puerto Rico) with the aim of investigating the origin of ionospheric electric fields in the frequency range of 0.01-2 cycles/h. In quiet times, atmospheric gravity waves appeared to be the most likely source of the ionospheric electric field. This hypothesis was tested by a direct simultaneous comparison of measurements of gravity waves in the mesosphere and of electric fields in the thermosphere during very quiet conditions. The results indicated that a gravity wave source is a plausible candidate for the electric field fluctuations.

Nanometer scale structure fabrication with the scanning tunneling microscope

Abstract: Nanometer scale structures have been produced on atomically flat surfaces of metallic glasses using the scanning tunneling microscope in the tunneling mode with enhanced local current densities and strong electric fields. Depending on the current and the electric field enhanced diffusion, local crystallization of the glassy state or Taylor cone formation of the locally molten surface can occur. These structures provide a potential means of studying the behavior of matter at nanometer dimensions.