Showing papers on "Electric potential published in 1969"
TL;DR: In this article, the effect of various electromagnetic boundary conditions on the propagation of surface waves in piezo-electrics is considered and an analytic expression for this impedance is found in the case of weak piezoelectric coupling which permits the calculation of the phase velocity for arbitrary values of the impedance.
Abstract: The effect of various electromagnetic boundary conditions on the propagation of surface waves in piezo‐electrics is considered. Basic for the analysis is the introduction of an electric ``surface impedance'' which relates the electric potential to the normal component of electric displacement in the surface. An analytic expression for this impedance is found in the case of weak piezoelectric coupling which permits the calculation of the phase velocity for arbitrary values of the impedance. It is also shown that within the weak coupling approximation the surface impedance contains the information on material parameters necessary for calculating the power transferred to surface waves from an impressed electric current.
269 citations
TL;DR: In this article, the dielectric response of a semi-infinite metal to a point charge a short distance outside its surface is calculated in the linearized Fermi-Thomas approximation.
Abstract: The dielectric response of a semi‐infinite metal to a point charge a short distance outside its surface is calculated in the linearized Fermi–Thomas approximation. The general form of the potential in the metal and vacuum is discussed. A generalization of the classical image theorem is given. The energy change on bringing up the charge to the surface is calculated, and found to be in good agreement with a previous approximation due to Gomer and Swanson.
129 citations
TL;DR: In this paper, a new method of solving the linear Debye-Huckel (D.H.) equation for the electric potential in the overlapping diffuse layers of two identical, spherical, colloidal particles at separation R is described.
110 citations
TL;DR: In this article, the saturation current of a sphere at a large positive potential ϕ can draw from a surrounding collisionless plasma in a magnetic field is investigated, assuming that the ions are excluded from the region of high potential surrounding the sphere, thus presenting an increased cross-sectional area through which electrons can be collected from the plasma along magnetic field lines.
Abstract: The limitation on the current that a sphere at a large positive potential ϕ can draw from a surrounding collisionless plasma in a magnetic field is investigated. The model assumes that for eϕ ≫ kTe the ions are excluded from the region of high potential surrounding the sphere. This region increases in size as ϕ increases, thus presenting an increased cross-sectional area through which electrons can be collected from the plasma along magnetic field lines. We suggest that there is a critical density at which the electron cloud surrounding the positive body is sufficiently turbulent that the electrons are free to diffuse radially across magnetic field lines and thereby reach the sphere. This model yields a saturation current I ∝ ϕ/lnϕ, which scales directly with the density, thermal velocity, and square of the body size. At high background electron concentrations a space-charge-limited flow model that predicts I ∝ ϕ6/7 is more applicable, whereas the more pessimistic limit of I ∝ ϕ1/2, which follows from the conservation of the single particle constants of motion in time invariant electric and magnetic fields, is appropriate when the background electron concentration is low.
101 citations
TL;DR: In this article, the potential distribution between the electrodes at two stages in the spark development has been investigated and it has been shown that the resulting maximum electron density eventually causes a rapid increase in dissociation of molecular hydrogen on the axis of the discharge brought about by a rise in the gas temperature.
Abstract: Streak photography has been used to supplement the earlier shutter photo. graphic investigation of Doran and Meyer (1967) using the same coaxial cable discharge circuit. Additional information has also been obtained from measurement of the potential distribution between the electrodes at two stages in the spark development. Redistribution of space charge is shown to give rise firstly to a transient diffuse glow discharge that has a close similarity with a normal d.c. glow discharge. It has also been shown that, even while the diffuse glow discharge expands, a partial constriction occurs in which most of the current flows along a narrow axial column. The resulting maximum in electron density eventually causes a rapid increase in dissociation of molecular hydrogen on the axis of the discharge brought about by a rise in the gas temperature. Owing to its greater electrical conductivity this axial column soon carries the entire current and the discharge becomes filamentary though still being maintained by a high cathode fall field, which exists until a sudden change in the cathode mechanism gives rise to the low voltage arc channel. Both the filamentary glow and arc columns are observed to expand according to an r cc ti law.
49 citations
49 citations
TL;DR: In this article, the Langmuir type probes on Explorer 31 were used to obtain electron current, space potential and ionic composition for disturbance region dependence on ionic compositions, and the results showed that the current and potential were determined by the ionic properties of the environment.
43 citations
41 citations
TL;DR: In this paper, electric field effects have been detected in the 14N N.M.R. spectra of nitrobenzene and nitromethane and showed that the Lorentz and Onsager local field models are not valid in these liquids at room temperature.
Abstract: Electric field effects have been detected in the 14N N.M.R. spectra of nitrobenzene and nitromethane. Application of an electric field induces molecular alignment in the liquid. The quadrupolar interaction is then not averaged out and line splitting results. The alignments measured in the pure liquids show that the Lorentz and Onsager local field models are not valid in these liquids at room temperature. Comparison of the measured alignments of nitrobenzene with those obtained from the Kerr effect show fair agreement. Double quantum transitions have been detected in the electric field N.M.R. spectrum of nitromethane.
40 citations
Journal Article•
TL;DR: In this article, the authors studied diurnal and seasonal variations of atmospheric electric potential gradient and the effect of wind on them, with the recordings over a period of 1 yr at this station.
Abstract: Diurnal and seasonal variations of atmospheric electric potential gradient and the effect of wind on them, have been studied, with the recordings over a period of 1 yr at this station. Negative potential gradients, observed in high wind speeds, are explained by arguing the dust particles to be negatively charged. Further, reasons are given in favour of free convection as a possible cause of sunrise effect.
33 citations
TL;DR: In this paper, a weakly ionized plasma will go unstable in the presence of a density gradient and parallel electric field, both at right angles to a magnetic field, if the electric field is of the right sign and sufficiently large.
Abstract: A weakly ionized plasma will go unstable in the presence of a density gradient and parallel electric field, both at right angles to a magnetic field, if the electric field is of the right sign and sufficiently large. The nonlinear limit of the first mode to go unstable when E is increased is determined as a function of Δ [Δ ≡ (E ‐ Ec)/Ec]. A general theory of this small amplitude behavior is used. The mode amplitude, frequency shift, density flattening, electric field change, and anomalous plasma transport are obtained as functions of Δ. It is shown that mode coupling corrections are small, and hence that the quasilinear result is sufficient.
TL;DR: In this paper, a theoretical study of the convection near a heated vertical plate in a dc electric field is made, where a set of boundary-layer equations are developed and then integrated over the boundary layer.
Abstract: A theoretical study is made of the convection near a heated vertical plate in a dc electric field. Electrical forces are produced by a bulk charge density in an electric field. This charge density occurs because the temperature gradients produce gradients in conductivity in a fluid with Ohmic electrical properties. To find the effect of the electrical forces, a set of boundary‐layer equations is developed and then integrated over the boundary layer. This integration produces ordinary differential equations when profiles are assumed for the temperature, velocity, and electric field. These profiles each have the same boundary‐layer thickness. Both numerical and analytical solutions are found for these equations. The analytical solutions are for special cases and approximate the numerical solutions. The results are approximate expressions for the temperature, velocity, electric field, and heat transfer from the plate.
TL;DR: In this paper, the authors used a directional sensitive detector to reveal the appearance of'shading' of surface detail, revealing more clearly the nature of shallow undulations, with a three-dimensional effect similar to that obtainable by optical microscopy with side illumination.
Abstract: Directionally sensitive detectors have been used in the scanning electron microscope to reveal additional detail due to deflection or non-uniformity of the spatial emission distribution of the secondaries which form the electron picture of the surface under examination. Deflection may occur as a result of electric or magnetic fields above the surface; also the emission characteristic may be anisotropic, or modified in shape and direction by local surface structure. These effects all occur in addition to the principal source of contrast in the scanning electron microscope, i.e. changes of secondary emission coefficient. The directional content of contrast is normally small, but the system discussed causes considerable enhancement of these effects. Results have the appearance of `shading' of surface detail, revealing more clearly the nature of shallow undulations, with a three-dimensional effect similar to that obtainable by optical microscopy with side illumination. Comparative results are presented which indicate the advantages to be gained for examination of small surface detail. By appropriate adjustment of electrostatic bias on electrodes, the detector system can provide magnetic contrast, potential contrast due to changes in surface electric potential, electric contrast from horizontal electric fields and improved sensitivity to surface topography. To a considerable extent these can be separately identified by observation under several different detector field configurations.
TL;DR: In this article, the electric permittivity of a composite can be expressed in terms of the average of the electric potential on the surface of a filler particle and the expression obtained is developed in powers of the volume fraction c of filler particles.
Abstract: The electric permittivity of a composite can be expressed in terms of the electric permittivity of the components and the average of the electric potential on the surface of a filler particle. The expression obtained is developed in powers of the volume fraction c of filler particles. Both the term linear in c and the term which is quadratic in c . are derived explicitly for two systems: (a) the particles are spheres; (b) the particles are circular cylinders perpendicular to the external field. Two methods are used. The first is an approximate treatment which is based on successive "reflections" of the perturbation caused by one particle off a second particle. The assumption is made that each reflection can be calculated as though the perturbation of the field is seen by the particle as a homogeneous field. This approach is worked out for cylinders and for spheres. The second method is carried through only for cylinders. It is based on the use of bipolar coordinates and is rigorous. The results obtained a...
TL;DR: In this paper, a method for computing the potential and electric field in the gap between unipolar twin-bundle conductors and ground based on a charge simulation technique and the principle of images is described.
Abstract: A knowledge of the electric field is required to estimate the onset voltages of corona breakdown for extra-high voltage lines with bundle conductors. A method is described for computing the potential and electric field in the gap between unipolar twin- bundle conductors and ground based on a charge simulation technique and the principle of images. In this method the charge on the conductors is represented by several lumped charges. Boundary conditions on the conductor's surface allow formulation of simultaneous equations, whose digital solution yields the assumed lumped charges, from which the potential and electric field are directly computed. The digital computer program provided values of the potential and electric field, magnitude, and direction, anywhere in the gap with an accuracy of 0.1 percent. The results of a sample calculation for an actual 345-kV conductor are given for varying parameters.
TL;DR: In this article, a single-particle propagator for a free electron in a uniform electric field is presented, in its time-dependent form, taking simple closed forms in both momentum and configuration space.
Abstract: A calculation is presented of the single-particle propagator for a free electron in a uniform electric field. In its time-dependent form this takes simple closed forms in both momentum and configuration space. Series expansions for the Fourier transform of the configuration-space propagator are given. Using the latter a calculation is made of the electric-field dependence of the (approximate) bound state of the delta-function potential. A variational method which is suitable for general potentials is also given.
TL;DR: In this paper, the retarding potential difference (RPD) technique was used for improving the electron energy resolution. But the RPD data collection was performed automatically by the analyzer, and the tedious labor involved in obtaining RPD signals by conventional means, and its subsequent arithmetic reduction, was all performed automatically.
Abstract: A commercially available multichannel analyzer, used in the multiscaling mode, has been adapted so as to accumulate automatically data from electron beam experiments employing the retarding potential difference (RPD) technique for improving the electron energy resolution. The electron accelerating voltage is generated by digital‐to‐analog conversion of the ``live'' channel address, the lower and upper limits of the sweep being adjustable over a wide range. The analyzer is swept alternately in the add and subtract modes with a period which is short compared to possible drifts in electron current, collision chamber pressure, multiplier sensitivity, etc. The tedious labor involved in obtaining RPD data by conventional means, and its subsequent arithmetic reduction, is all performed automatically by the analyzer. Examples of data obtained by the technique are presented, showing the improvement in signal to noise obtainable by operating for a suitably large number of sweeps.
TL;DR: In this paper, a simplified model for an accelerating electric field is proposed to explain the dependence on angle and energy on the precipitating mechanism of an auroral storm, and the results are applied to cases where the electric potential is small compared with the energy dispersion of trapped particles.
Abstract: Measurements of the distribution of auroral particles with energy and pitch angle have not given much of a clue to the precipitating mechanism, except to indicate that it occurs locally, in the magnetosphere. The available data, including observations of periodicities in auroral bombardment, hint that at least two different mechanisms are operative. With the aid of a simplified model for an accelerating electric field, the kind of dependences on angle and energy to be expected are illustrated. Quantitative discussion is restricted to cases where the electric potential is small compared with the energy dispersion of trapped particles, and the results are thus probably more applicable to instability mechanisms than to the electrostatic precipitation treated by Taylor and Hones. Simultaneous measures of the spectrum at different pitch angles above the atmosphere could be combined to test any given model of electric acceleration. In spite of the wealth of measurements, adequate data do not yet seem to be available.
TL;DR: In this paper, short term variations of electrical potential gradient have been studied during fair and disturbed weather and on days with and without wind, and the magnitude and frequency of the "agitation" are found to depend on the mean value of the potential gradient.
TL;DR: Hydrostatic pressures were applied to human teeth to investigate the development across the dentin of electric potentials which might be involved in excitation of sensory receptors.
Abstract: Hydrostatic pressures were applied to human teeth to investigate the development across the dentin of electric potentials which might be involved in excitation of sensory receptors. Electric potentials were measured, and an attempt was made to explain the phenomenon on the basis of the Helmholtz-Smoluchowski equation.
TL;DR: In this paper, the electric potential of liquid water on an ice surface was investigated both theoretically and experimentally, and it was shown that the electric properties at the ice surface were important in explaining the charge generation in thunderstorms, especially the explanation of positively electrified graupel pellets and hailstones.
Abstract: The existence of the electric potential of liquid water on an ice surface is investigated both theoretically and experimentally. The electric potential produced at the boundary surface between the liquid water and bulk ice is set up by the difference of the proton activation energy between liquid water and ice. Negative charge is developed on the side of liquid water and positive charge on the side of ice. The expected value of the potential of liquid water on ice is confirmed by the experiments on specimens of highly purified single crystals of ice. The electric properties of bulk ice have been considered to explain the electric charge generation of graupel pellets and hailstones. In this paper, it is shown that the electric properties at the ice surface were important in explaining the charge generation in thunderstorms, especially the explanation of positively electrified graupel pellets and hailstones. This idea is extended to explain the positive charge of snow crystals in the process of mel...
TL;DR: In this paper, numerical calculations of the temperature and the pressure profiles and the voltage-current characteristic of a cylindrical arc column with an applied axial magnetic field are presented.
Abstract: Presented are numerical calculations of the temperature and the pressure profiles and the voltage-current characteristic of a cylindrical arc column with an applied axial magnetic field. A radial pressure gradient is established by means of ambipolar diffusion of charged particles across the magnetic field and by means of the Nernst-Ettinghausen effect. Radiation losses are neglected. The dissociation of hydrogen molecules is taken into account, which has a great influence on the temperature profile and on the dissipated power if the axial temperature is not too high (<105 degrees K) Neglecting dissociation, as is often done, can lead to serious errors. The effect of the magnetic field on the dissipated power and the temperature profile is discussed.
TL;DR: In this article, the electric potential of an ice surface rubbed by a single crystal ice piece was investigated both theoretically and experimentally, and the negative electric potential on the rubbed ice surface increased with increasing number of dislocations on the ice surface.
Abstract: The electric potential of an ice surface rubbed by a single crystal ice piece was investigated both theoretically and experimentally. The negative electric potential on the rubbed ice surface increased with increasing number of dislocations on the ice surface. In order to explain this negative electric potential of a rubbed ice surface, it was assumed that negatively electrified dislocations and positively electrified D-defects were produced in pairs by rubbing. In the steady state, a potential difference is set up at the surface such that the surface becomes negative because of the much greater mobility of D-defects than dislocation. On the bases of some theoretical arguments it is predicted that the surface potential is −58 mV when the dislocation density at the ice surface is one order of magnitude larger than that in the interior of the ice. It is thought that these phenomena are of basic importance in the generation of positive electric charge of graupel pellets and hail at colder temperatures.
TL;DR: In this article, the basic physics of the processes producing flux flow resistance in superconductors is reconsidered and it is shown that in the dynamic intermediate state (in which at low fields flux tubes move through the material) there is no potential difference between the contacts; the measured voltage is produced by magnetic flux outside the superconductor which changes as each of the tubes move.
Abstract: The basic physics of the processes producing flux flow resistance in superconductors is reconsidered. It is shown that in the dynamic intermediate state (in which at low fields flux tubes move through the material) there is no potential difference between the contacts; the measured voltage is produced by magnetic flux outside the superconductor which changes as each of the tubes move. On the other hand, in a type 2 superconductor near Hc2 there is a potential difference between the contacts and no effect of changing magnetic flux. We make the conjecture that in general in the mixed state there are contributions of both types to the voltage measured (V), the fraction Vp/V produced by a potential difference in the superconductor decreasing as the field is lowered below Hc2. In all cases the measured voltage V is the same as if there were an electric field (ν × B)/c in the superconductor, where ν is the average velocity of the flux `entities' and B the flux density in the material. The low-frequency noise in superconductors corresponds to fluctuations in the component of voltage Vi produced by magnetic flux changes. This has the consequence that the noise spectrum should depend on the arrangement of the leads of the measuring circuit and also that the decrease in noise observed with increasing field in the mixed state corresponds to the decrease in the ratio Vi/V and does not necessarily represent a decrease in the size of the flux `entities' with increasing field.