Showing papers on "Electric field published in 1974"

Precipitating electron fluxes formed by a magnetic field aligned potential difference

Abstract: A model is developed in which a magnetic field aligned potential difference is assumed to accelerate electrons downward into the atmosphere. It is pointed out that the upgoing backscattered electrons produced by this electron beam may process insufficient kinetic energy to overcome the hypothetical potential difference. These electrons will be reflected downward to appear as members of a precipitating electron population. A numerical model was constructed in order to describe the total precipitating electron flux in terms of a primary accelerated beam and backscatter from the atmosphere. It is pointed out that many features that appear in the model beam are observed in the auroral electron beam as well. An example of an auroral beam, measured by Frank and Ackerson (1971), is compared favorably with a model electron beam formed by a parallel potential.

Kinetics and steady-state properties of the charged system controlling sodium conductance in the squid giant axon.

Abstract: 1. Asymmetries in the early time course of the displacement current passing across the membrane after application of equal voltage-clamp pulses in the two directions have been investigated in the squid giant axon. Before making the measurements, Na current was blocked by removal of external Na and treatment with tetrodotoxin. Potassium current was usually blocked by perfusion with CsF, but some experiments were done with intact axons. A signal averaging technique was used to eliminate the symmetrical components of the membrane current.2. The asymmetrical current had a contribution of appreciable size attributed to the movement of mobile charges or dipoles in the membrane. This was manifested as an outward current rising rapidly to a peak on depolarization of the membrane and then declining exponentially to zero, followed at the end of the pulse by an inward surge of current with a similar time course. There was also a sustained flow of current outwards during the pulse, arising from ionic leakage with a rectifying characteristic.3. The identification of the exponentially changing current component with the displacement of charged particles forming an integral part of the membrane was supported by the demonstration that the total transfer of charge was equal and opposite at the beginning and end of the pulse, that it reached saturation when the internal potential was taken to a sufficient positive value, and that its size was unaffected by temperature, although its time constant had a large temperature coefficient.4. The disposition of the mobile charges in the steady state was shown to obey a Boltzmann distribution. At the midpoint of the distribution curve, the proportion of the charge displaced underwent an e-fold change for a 19 mV change in potential. The effective valency of the particles, that is their actual charge multiplied by the fraction of the electric field acting on them, was therefore 1.3.5. The total quantity of mobile charge was estimated as about 1500 x 10(-12) C for 0.05 cm(2) of membrane, corresponding to some 1900 charges/mum(2).6. The identification of these mobile charges with the gating particles responsible for controlling Na conductance was supported by the findings that (a) their time constants were the same as those of Hodgkin & Huxley's ;m' system, both in absolute magnitude and in their dependence on potential and temperature, (b) the transition potential at which the charges were evenly distributed on the two sides of the membrane also agreed with that for the ;m' system in intact axons, and its value was similarly shifted in a positive direction by a reduction in internal ionic strength or by raising the external Ca concentration, (c) comparison of the steepness of the curves governing on the one hand the steady-state distribution of the mobile charges and on the other the Na conductance, suggested that an effective cooperation of the charges in groups of three was involved, again in excellent agreement with the ;m' system.7. Displacement of the mobile charges was unaffected by external pH over the range 5-8, but preliminary observations showed that 1% procaine reduced the total charge transfer to somewhat less than 40% of the initial value, and roughly halved the time constant.

Incoherent scatter measurements of E region conductivities and currents in the auroral zone

Abstract: Data taken by incoherent scatter radar have been used to investigate ionospheric conductivities and electrical currents. During quiet days, the conductivities appear to vary in a way consistent with ionization arising from solar EUV radiation. In the evening hours, enhancements in the northward electric field are found to precede small increases in the conductivities. Strong enhancements of the Hall conductivity relative to the Pedersen conductivity occur during negative bays when the electric field is in a southwestward direction. The ionospheric currents calculated in the geomagnetic east-west direction are in good agreement with the H component measured by a nearby magnetometer; this result indicates that the current causing the ground level magnetic fluctuations is a broad horizontal sheet current. The north-south ionospheric current, however, consistently disagrees with the observed D component in a manner that cannot easily be explained unless currents parallel to the earth's magnetic field are present.

Perturbation analysis for gravitational and electromagnetic radiation in a Reissner-Nordström geometry

Abstract: We consider the gravitational and electromagnetic fields produced by a charged (or uncharged) test particle moving in a Reissner-Nordstr\"om geometry as perturbations on the background Reissner-Nordstr\"om geometry and its associated electric field, respectively. The gravitational perturbations are expanded in tensor harmonics in the manner of Regge and Wheeler, while the electromagnetic field is expanded in vector harmonics. Following a previously proposed convention, we find that in the Einstein-Maxwell system of equations, electric gravitational multipoles couple only to electric (TM) electromagnetic multipoles and similarly for magnetic multipoles. It is possible to reduce the entire Einstein-Maxwell system for each type of multipole to two second-order Schr\"odinger-type equations.

Temperature- and field-dependence of hopping conduction in disordered systems, II

Abstract: A model is presented which allows the conductivity due to hopping between randomly distributed localized states to be calculated for any form of density of states This model has been applied analytically to the case of a flat density of states, and produces the Mott 1/T 1/4 relation at low temperatures, if the applied electric field is sufficiently low. The field-dependence of the conductivity is found to be log [sgrave] ∼ F 2 at low fields, and log [sgrave] ∼ 1/F 1/4 at very high fields.

Ionosphere-Magnetosphere Coupling

Abstract: A review is given of some aspects of the electric coupling between the ionosphere and magnetosphere. Topics discussed are the mapping of time-dependent electric fields, the effects of Birkeland currents on the magnetospheric plasma convection, the relation of Birkeland currents to ionospheric electric field structures such as field reversals, secondary Birkeland currents of ionospheric origin and triggering of auroral particle precipitation, double-layers causing voltage drops along the magnetic field lines, and an equivalent electric circuit for the substorm currents in the coupled ionosphere-magnetosphere system.

Theory of surface polaritons in anisotropic dielectric media with application to surface magnetoplasmons in semiconductors

Abstract: A theory is presented for surface polaritons associated with the planar surface of a semi-infinite anisotropic dielectric medium. Retardation is included. In general, two attenuating components with different attenuation constants must be superposed within the medium in order to satisfy the boundary conditions, and the macroscopic electric field vector does not lie in the sagittal plane. For special cases, however, only one attenuating component is required, and the electric vector does lie in the sagittal plane. The theory is applied to the specific case of surface magnetoplasmons in a semiconductor for magnetic fields either perpendicular or parallel to the surface. In the latter case, propagation directions parallel and perpendicular to the magnetic field are considered. Possibilities for the experimental observation of the effects predicted are discussed.

Apparatus for promoting healing processes

Abstract: An apparatus for promoting healing of body tissue composed of a coil arranged to be applied to the affected body part and to be connected to a low frequency a.c. source to produce a magnetic field within the region to be treated, and at least two sheetlike electrodes associated with the coil and spaced from one another, the electrodes being arranged to be located at respectively opposite sides of the region to be treated and to be connected to a source of a low frequency voltage to produce an electric field within the region to be treated at the same time as the magnetic field.

The average auroral zone electric field

Abstract: Four hundred and seventy-eight hours of electric field data obtained by the flight of 32 balloons between L = 5.4 and L = 8.2 have been averaged to determine mean properties of the auroral zone electric field. The results are understood in terms of a model in which the two-cell convection pattern is rotated about the sun-earth line by an amount that depends on the sign and magnitude of the y component of the interplanetary magnetic field. This model and the data suggest either that important parallel potential drops exist along auroral zone magnetic field lines or that simple conjugacy between the two hemispheres does not exist along such field lines.

High-latitude electric fields and the three-dimensional interaction between the interplanetary and terrestrial magnetic fields

Abstract: More than 200 hours of ionospheric electric field measurements taken on balloons flown from three polar cap sites have been analyzed to determine average properties of the large-scale polar cap electric field and its dependencies on the interplanetary magnetic field. The major component of this electric field was directed from dawn to dusk and produced an average polar cap potential drop of about 55 kV. The magnitude of this potential provides an upper limit of about 700 RE for the length of the magnetospheric tail and implies an energy input from the solar wind to the magnetosphere of about 5 × 1019 ergs/sec. The dawn to dusk component of the high-latitude polar cap electric field responds to Bz, the northward component of the interplanetary magnetic field, on a time scale ≲1 hour and with an average increase of about 3 mV/m for each 1 γ decrease of Bz. The hourly averages of the electric field data at each of the three sites are well described by a two-cell convection pattern whose location depends on the y component of the interplanetary magnetic field. When By is positive (negative), the two-cell convection pattern shifts toward dawn (dusk) in the northern hemisphere with the following consequences: the maximum intensity of the northern polar cap dawn to dusk electric field component occurs at local morning (evening), and the auroral zone return flow reaches higher latitudes in the evening (morning). Evidence of the vector nature of the interaction between interplanetary and terrestrial magnetic fields is provided by the observation that the above By dependent signatures are most evident when Bz is most negative.

Finite-Element Solution of the Eddy-Current Problem in Magnetic Structures

Abstract: Analysis of the eddy-currentproblem in magnetic structures by the method of Finite-elements is presented. The linear diffusion equation representing the appropriate energy functional is described. The field region is discretised by triangular Finite-elements and the solution to the field problem is obtained by minimizing the energy functional with respect to each of the vertex values of the vector potential. Expressions for the magnetic field, electric field and eddy-current losses are presented. The method is applied to a few cases of engineering interest and compared with results of classical analysis and tests.

Effect of an external electric field on the yield of free ions. I. General results from the Onsager theory

Abstract: Onsager's equation for the effect of an external electric field on the probability of an isolated ion pair escaping neutralization in a dielectric medium has been rearranged for evaluation in a consistent way. The present treatment allows the escape probability to be written as a single series valid for arbitrary field strengths and initial separations. In a given case, procedure is outlined for calculating this probability in the most systematic manner. Although expansion of the escape probability in powers of the external field is not advisable at high field strengths because of the slowness of convergence, the field coefficients are provided for evaluation and comparison at relatively low fields. At high fields possibility of a temperature inversion effect is indicated; that is, the field‐dependent escape probability may actually decrease with temperature.

The Detection of Electric Fields from Electric Organs

Abstract: In the preceding chapter some aspects of the biological role of electroreception are discussed that depend on signals arising from other organisms and from inanimate sources. In the present chapter we consider the reception of signals from electric organs, both from the same individual and from others.

Measurements of electric fields in thunderclouds

Abstract: A series of measurements of electric fields inside active thunderclouds in central New Mexico with instrumented rockets shows that very intense fields (up to 4×105 V/m) do exist, although they are rare. In a tabulation of the peak values of the electric field along each trajectory, 4.3×104 V/m is the median value. Peak values greater than 105 V/m were encountered only 6 times out of a total of 61 cases. Two examples of very intense fields are presented as case studies.

Effect of localized electric fields on the evolution of the velocity distribution function

Abstract: The interaction between charged particles and sharply localized fields is investigated. The random particle scattering is described by a Fokker-Planck equation whose time-dependent solution exhibits the formation of a highly populated superthermal tail.

Electric field dependence of the dielectric constant of PZT ferroelectric ceramics

Abstract: Bias (dc electric field) dependence of the dielectric constant of ferroelectric ceramics of the Pb(Zr,Ti)O3 type has been investigated. Measurements were carried out at various temperatures in the ferroelectric phase and at several frequencies between 1 kHz and 1 MHz. The bias characteristics of the dielectric constant show a temperature‐dependent asymmetry in the electric field direction. A model in which the coercive fields of the 180° and 90° domains are distributed around some average value is considered. The total dielectric constant of the material is calculated by considering the contributions of each type of domain, taking into account the difference between the differential and incremental dielectric constants. This model explains the dependence of dielectric constant on electric field. A comparison of the calculated and experimental results is presented.

Energetic particle distribution in a toroidal plasma with neutral injection heating

Abstract: The energetic ion distribution resulting from the injection of high‐energy neutrals into a toroidal plasma has been derived. An appropriate kinetic equation which contains the angular scattering, friction, and diffusion of the energetic ions by the background particles, charge exchange on the background neutrals, and acceleration of the ions by the electric field has been solved analytically by use of the WKBJ method. Collisions of the energetic ions with the faster moving electrons results in some of the ions increasing their energy above the injection energy. The width of this ``high‐energy tail'' is shown to depend upon the electron temperature and the electric field. An estimate of the effect upon the width of this tail of collisions between the energetic ions themselves is also given. Finally, illustrated examples of the various significant physical processes are presented.

Ponderomotive-Force Effects in a Nonuniform Plasma

Abstract: The effect of the ponderomotive force in the interaction of a capacitor rf field with a nonuniform plasma is investigated.

Application of the molecular dynamics method to a liquid system with long range forces (Molten NaCl)

Abstract: A significant and characteristic difficulty arising in the use of statistical mechanics to describe the properties of fused salts is due to the extreme range of the electrostatic field; an accurate representation of the Coulomb energy and Coulomb forces may be obtained using Ewald's expansion. Such calculations are tested here on the model case of liquid NaCl at different temperatures. In addition, this method is applied to the description of ionic media by molecular dynamics computations. (A Born-Huggins-Mayer pair potential is used with constants derived from the solid at 298 K.) This treatment introduces cut-off distances and periodic boundary conditions. The influence of these constraints on the conservation of energy and momenta is investigated. Thermodynamic properties of molten NaCl at 1164·5, 1224·5 and 1340·5 K are calculated. The motions of individual ions, anions and cations are described in terms of a velocity self-correlation function and their diffusion coefficients are determined.

Long journey into tunneling

Abstract: N 1923, during the infancy of the quantum theory, de Broglie [ 11 introducted a new fundamental hypothesis that matter may be endowed with a dualistic natureparticles may also have the characteristics of waves. This hypothesis, in the hands of Schrodinger [2] found expression in the definite form now known as the Schrodinger wave equation, whereby an electron or a particle is assumed to be represented by a solution to this equation. The continuous nonzero nature of such solutions, even in classically forbidden regions of negative kinetic energy, implies an ability to penetrate such forbidden regions and a probability of tunneling from one classically allowed region to another. The concept of tunneling, indeed, arises from this quantum-mechanical result. The subsequent experimental manifestations of this concept can be regarded as one of the early triumphs of the quantum theory. In 1928, theoretical physicists believed that tunneling could occur by the distortion, lowering or thinning, of a potential barrier under an externally applied high electric field. Oppenheimer [3] attributed the autoionization of excited states of atomic hydrogen to the tunnel effect: The coulombic potential well which binds an atomic electron could be distorted by a strong electric field so that the electron would see a finite potential barrier through which it could tunnel. Fowler and Nordheim [4] explained, on the basis of electron tunneling, the main features of the phenomenon of electron emission from cold metals by high external electric fields, which had been unexplained since its observation by Lilienfeld [SI in 1922. They proposed a one-dimensional model. Metal electrons are confined by a potential wall whose height is determined by the work function 9 plus the Fermi energy E/, and the wall thickness is substantially decreased with an externally applied high electric field, allowing electrons to tunnel through the potential wall, as shown in Fig. 1. They successfully derived the well-known Fowler-Nordheim formula for the current as a function of electric field F: J = AF* exp [-4(2nr)1'*t$a'*/3kF]. An application of these ideas which followed almost immediately came in the model for a decay as a tunneling process put forth by Gamow [6] and Gurney and Condon [7]. Subsequently, Rice [8] extended this theory to the description of molecular dissociation. The next important development was an attempt to invoke tunneling in order to understand transport properties of electrical contacts between two solid conductors. The problems of metal-to-metal and semiconductor-to-metal contacts are important technically, because they are directly related to electrical switches and rectifiers or detectors.