Showing papers on "Electric potential published in 1972"

A local exchange-correlation potential for the spin polarized case: I

Abstract: The local density theory is developed by Hohenberg, Kohn and Sham is extended to the spin polarized case. A spin dependent one- electron potential pertinent to ground state properties is obtained from calculations of the total energy per electron made with a 'bubble' (or random phase) type of dielectric function. The potential is found to be well represented by an analytic expression corresponding to a shifted and rescaled spin dependent Slater potential. To test this potential the momentum dependent spin susceptibility of an electron gas is calculated. The results compare favourably with available information from other calculations and from experiment. The potential obtained in this paper should be useful for split band calculations of magnetic materials.

Influence of Microwave Radiation on Current‐Voltage Characteristic of Superconducting Weak Links

Abstract: The current‐voltage characteristics of microwave‐irradiated superconducting weak links have been calculated on the analog computer. Experimental results of several authors can be interpreted correctly by taking into consideration the resistive feedback.

Experimental Observation of Pair-Quasiparticle Potential Difference in Nonequilibrium Superconductors

Abstract: It is shown experimentally that when a quasiparticle current is converted into a pair current in a superconductor, the quasiparticle potential in the nonequilibrium region differs from the pair chemical potential.

High‐Frequency Response of Josephson Point Contacts

Abstract: For a current‐driven Josephson junction shunted by an Ohmic resistance, the dc voltage response and impedance to external high‐frequency currents is calculated with a second‐order perturbation method based on the unperturbed solution for the time evolution of the voltage as given by Aslamazov and Larkin. The response is proportional to signal power and has three characteristic‐frequency regions depending on whether the internal self‐generated Josephson frequency, ω0, is larger than, equal to, or smaller than the signal frequency, ω. For ω0 ω the response could be expressed by easily observable parameters of the dc voltage‐current characteristics. This permits comparison of the predictions with experimental results obtained on point‐contact junctions whose dc characteristics were only approximately represented by the simple model chosen for analysis. For ω0≪ω the response is found to be proportional to (i) the slope of the dc characteristic, (ii) the inverse square of the applied frequency, (iii) the inverse battery current in terms of the critical current, and (iv) the voltage amplitude of the inherent Josephson oscillations. For ω0≫ω ``classical'' detection proportional to curvature is obtained. For ω0∼ω resonance detection occurs, which depends to a considerable degree on fluctuations of the average contact voltage. These predictions are in reasonable agreement with experiments in which point‐contact junctions were illuminated with klystron radiation at 10 and 90 GHz. Evidence is presented that the voltage fluctuations limiting the resonance response are the result of noise generated in the junction. Comparison of the noise‐equivalent power expected from the simple model with measured results suggests that parasitic elements, such as shunt capacity, are not negligible at 90 GHz.

Electric fields in the magnetosphere

Abstract: Two techniques, tracking the motions of Ba(+) clouds and measuring the differences in floating potential between symmetric double probes, were successful in: (1) demonstrating the basic convective nature of magnetospheric electric fields, (2) mapping global patterns of convection at upper ionosphere levels, and (3) revealing the physics of electric currents in the ionosphere and the importance of magnetosphere-ionosphere feedback in altering the imposed convection.

Polaron Bound in a Coulomb Potential

Abstract: We have calculated the shift in ground-state energy of an electron bound in a Coulomb potential in a crystal, to second order in the electron-phonon coupling and for arbitrary values of the electron-impurity coupling.

A selfconsistent calculation of the rigid neutral atom density according to the auxiliary neutral atom model

Abstract: A selfconsistent calculation of the displaced charge density n'(r) around a completely screened ionic potential V0 in a metal has been carried out for the Hartree-Fock-Slater equations. V/sub /0 is the sum of the true ionic core potential Vion and the potential of a given (auxiliary) screening charge density nu (r). The resulting selfconsistent potential V'(r) is used to calculate the rigid neutral atom density n(r) which allows an approximate calculation of the metal selfconsistent potential. The main part of this work deals with the selfconsistent numerical calculation of the density n'(r) displaced by V0. The following approximations are made. The Kohn and Sham one-body formulation of the many-body problem is used. The wave equation is solved numerically inside a sphere of large but finite radius. The Coulomb potential due to the outer displaced charge is approximately calculated from the Friedel asymptotic formula. The continuous integration over the Fermi sea energy levels is replaced by a discrete summation. Selfconsistency is achieved by the use of a modified iterative process, using the linearized Thomas-Fermi equation in order to deal with the long range character of the Coulomb interaction. The method has been applied to metallic lithium and sodium, and results are given for n(r), on-the-Fermi-shell scattering matrix and nonstructural band structure properties.

Ionizing potential waves and high-voltage breakdown streamers.

Abstract: The structure of ionizing potential waves driven by a strong electric field in a dense gas is discussed. Negative breakdown waves are found to propagate with a velocity proportional to the electric field normal to the wavefront. This causes a curved ionizing potential wavefront to focus down into a filamentary structure, and may provide the reason why breakdown in dense gases propagates in the form of a narrow leader streamer instead of a broad wavefront.

Area influences and floating potentials in Langmuir probe measurements

Abstract: Influence of small reference electrode in Langmuir probe measurement of plasma density and temperature

Display device comprising a profusion of naked droplets of cholesteric liquid crystal in a substantially continuous polymeric matrix

Abstract: This disclosure is directed to articles of manufacture, chiefly display devices, containing minute "naked" droplets or inclusions of cholesteric liquid crystal material in a substantially continuous polymeric matrix, said liquid crystal material changing color or shade of color not only upon application of an electric potential but also upon removal of the field. The image produced has a comparable outline to that of the path of the electric field. Three chromatic states are evident, the normal color (before the electric potential is applied), the color given off when the electric field is applied, and the color observed when the electric field is removed. All three chromatic states are readily discernible from one another. The polymer matrix protects the cholesteric liquid crystal droplets from aging and enhances electric field behavior because the third chromatic state (electric potential removed) has a greater longevity with the matrix-bound material versus unprotected material of identical composition but no polymeric matrix. Other advantages are also discussed.

Electric Potentials near a Superconducting-Normal Boundary

Abstract: Measurements have been made within a few micrometers of a current-carrying superconducting-normal boundary, which indicate that an electric potential exists in the superconductor in this region Near the transition temperature the experimental results are consistent in magnitude and temperature dependence with a theory recently proposed by Rieger, Scalapino, and Mercereau

Electric Fields in the Magnetosphere and the Origin of Trapped Radiation

Abstract: According to experimental data there are essential differences in the dynamics of trapped particles with magnetic drift periods more than and less than ≈ 1 h. The behaviour of the particles with fast drift (radiation belt particles) can be well described by the theory of diffusion resulting from sudden impulses. The considerably faster rate of transport of lower-energy particles implies the existence of low-frequency electric fields of large amplitude, the influence of which on energetic particles is reversible. The low-frequency fields are one of many interconnected effects, including particle variations, induction of ionospheric current systems, development of active forms of auroras, formation of D st , etc. A probable cause of these events is the appearance and evolution of a plasma ring asymmetric in longitude in the trapped radiation region. The asymmetry may be brought about both by particle injection into the magnetosphere and by penetration of an external electric field into the trapped radiation region. On the assumption that the ionosphere is connected with the magnetosphere by currents along the lines of force, ensuring quasineutrality, and that an electric potential develops when these currents close in the E-layer, it is possible to show that the electric fields and current systems DP-1 and DP-2 are the lowest modes of the system of eigenfunctions of the problem of relaxation of an asymmetric plasma cloud.

Errors in retarding potential analyzers caused by nonuniformity of the grid-plane potential

Abstract: One aspect of the degradation in performance of retarding potential analyzers caused by potential depressions in the retarding grid is quantitatively estimated from laboratory measurements and theoretical calculations. A simple expression is obtained that permits the use of laboratory measurements of grid properties to make first-order corrections to flight data. Systematic positive errors in ion temperature of approximately 16% for the Ogo 4 instrument and 3% for the Ogo 6 instrument are deduced. The effects of the transverse electric fields arising from the grid potential depressions are not treated.

Mapping of the electric field of the Sq current into the lower atmosphere

Abstract: The electric field of the geomagnetic Sq current is mapped into the lower atmosphere. Equipotential surfaces of this potential field are calculated depending on altitude, latitude, and local time. It is shown that at balloon altitudes the horizontal components of this field have magnitudes about 1/10 of the thunderstorm-generated main geoelectric field. At the ground, the Sq field is about 5% of the main field.

Rotatory Motion of Dipolar Molecules Constrained by a Steady Electric Field

Abstract: In this paper a calculation has been carried out on the rotatory diffusion of dipolar rodlike molecules in the presence of an electric field. The time correlation method is used for calculations of dynamic susceptibilities. This calculation has been shown to be in good agreement with the dynamic dielectric studies of Block and Hayes. In addition, the decay of electric birefringence (Kerr effect) in the presence of an electric field has been shown to be extremely sensitive to the relative magnitudes of the steady state field and the initially applied sensing field.

Coulomb Potential in Ionic Crystals by Direct Summation

Abstract: A method is proposed to determine the shape and size of the finite crystal piece to be used in the calculations of the Coulomb potential at points in the unit cell of ionic crystals. The Coulomb potential at a point is calculated by direct summation of the potentials of all the ions in this finite crystal piece. A theorem was established which helps to make the resulting series in the calculations converge much faster, thus cutting the computing time by a factor of millions or more, depending on the accuracy desired. With the help of this theorem, it was possible to calculate the Coulomb potential at a grid of points in the unit cells of NaCl and CsCl structures to 10 decimal places. The Madelung constant for NaCl structure was calculated to 25 decimal places as an illustration of the power of this theorem.

Über den Fallraum in einer zylindrischen Hohlkathode / On the Cathode Fall in a Cylindrical Hollow Cathode

Abstract: Abstract The electric field distribution in the cathode fall and the current-voltage characteristic of a cylindrical hollow cathode are calculated on a purely radial model. The theoretical characteristic is compared with results measured on a H2-and Ar-discharge. From the experimental data, the current density ratio of electrons and ions on the cathode can be calculated. This ratio appears in the correct order of magnitude only if the carrier generation in the cathode fall is taken into account. Comparisons are made with the results of linear theories.

On the Electric Field of a Moving Test Charge

Abstract: The electric field at large distances from a moving test charge in a collisionless plasma is calculated. Significant differences from the well-known inverse fourth-power dependence of the electric field on the distance between the observer and the charged particle are obtained.

Pictures of Dynamic Electric Fields

Abstract: The electric field of a point charge moving at relativistic velocities along a single plane of motion may be visualized in a physically intuitive way with the aid of pictures of the electric lines of force. A general derivation of exact parametric equations for these lines of force is described and applied to create the pictures presented here of synchrotron radiation, low-angle high-energy Coulomb scattering, abrupt linear acceleration of a charge, and a charge undergoing simple harmonic motion.

Electric Deflection of Molecular Beams of Carbon Suboxide and Carbon Subsulfide

Abstract: The deflection behavior of molecular beams of C3O2 at 200 and 300°K and C3S2 at 300°K has been studied in inhomogeneous electric fields. Both species show net defocusing of the scattered beam with applied field. By comparison with the bent molecule NO2 whose electric dipole moment is known, upper limits of 0.15 D were placed on the electric moments of C3O2 and C3S2. These limits, coupled with extimates of the integrated absorption intensities obtained from published spectra for the ν7 vibration, permit upper limits of 0.15 rad to be placed on the bending angle. The most probable configuration is thus linear.

The Hall Effect in a Flowing Electrolyte

Abstract: This experiment demonstrates that a charged particle moving through a magnetic field experiences a force qv × B. When a saltwater solution flows through a magnetic field, the positive and negative ions are separated by the Lorentz force and establish an electric field. This field is measurable by means of the potential, or Hall voltage, developed across the flow tube.

One dimensional hydrogen atom with a repulsive core.

Abstract: The problem of an electron moving in a one dimensional Coulomb potential e2/ mod x mod is of interest in connection with the energy levels of the hydrogen atom in a strong magnetic field It is shown that the ground state energy of the one dimensional hydrogen atom is profoundly changed if a repulsive core is included in the Coulomb potential The sensitivity of the ground state energy to this repulsive potential is investigated and it is found that if the core is sufficiently 'hard' the ground state energy is very nearly the first Balmer energy The results appear to be relevant to the Yafet-Keyes-Adams theory of a hydrogen atom in a strong magnetic field and suggests that this theory may need modification