Showing papers on "Electric field published in 1975"

Electron and hole drift velocity measurements in silicon and their empirical relation to electric field and temperature

Abstract: The drift velocity of electrons and holes in silicon has been measured in a large range of the electric fields (from 3 . 102to 6 . 104V/cm) at temperatures up to 430 K. The experimental data have been fitted with a simple formula for the temperatures of interest. The mean square deviation was in all cases less than 3.8 percent. A more general formula has also been derived which allows to obtain by extrapolation drift velocity data at any temperature and electric field.

Three-Dimensional Induced Polarization and Electromagnetic Modeling

Abstract: The induced polarization (IP) and electromagnetic (EM) responses of a three‐dimensional body in the earth can be calculated using an integral equation solution. The problem is formulated by replacing the body by a volume of polarization or scattering current. The integral equation is reduced to a matrix equation, which is solved numerically for the electric field in the body. Then the electric and magnetic fields outside the inhomogeneity can be found by integrating the appropriate dyadic Green’s functions over the scattering current. Because half‐space Green’s functions are used, it is only necessary to solve for scattering currents in the body—not throughout the earth. Numerical results for a number of practical cases show, for example, that for moderate conductivity contrasts the dipole‐dipole IP response of a body five units in strike length approximates that of a two‐dimensional body. Moving an IP line off the center of a body produces an effect similar to that of increasing the depth. IP response va...

The motion of a proton in the equatorial magnetosphere

Abstract: A proton of low energy moving in the equatorial plane of the earth will experience drift motions due to both the magnetic field (magnetic gradient drift only, if the field is assumed to be that of a dipole) and the electric field The electric drift again separates into two parts - the drift due to the main electric field (or convection electric field) existing in the frame of the earth, and that due to the earth's rotation One result indicated by this work is that at distances of 4 - 6 earth radii, a transition from trapped proton orbits to open trajectories leading to the tail occurs at about 10 kev, the precise value depending upon local time Such a transition also seems to be indicated by particle observations using Explorer 45 The energy spectrum (at magnetically quiet times) of equatorial protons above this energy can be explained by charge exchange but increased flux observed below it seems to be related to the influx of particles on open orbits from the tail

Onsager mechanism of photogeneration in amorphous selenium

Abstract: The Onsager theory of dissociation has been used to explain the electric field, excitation wavelength, and temperature dependence of photogeneration in amorphous selenium. The Onsager theory was formulated to explain the departure from Ohmic behavior in either weak electrolytes or solid dielectrics, and the analysis of charge separation was carried out using the theory of Brownian motion of one particle under the action of Coulomb attraction and the collecting field. Both the absolute magnitude and functional dependence on electric field of the photogeneration efficiency in amorphous selenium at any excitation wavelength can be unambiguously explained using a single parameter which is the initial separation between thermalized electron-hole pairs. This initial separation varies from 7.0 nm at 400-nm excitation to 0.84 nm at 620-nm excitation. The application of the theory to the measured photogeneration data also leads to the important conclusion that each absorbed photon creates a pair of thermalized carriers bound by their mutual Coulomb attraction. The low quantum efficiency measured for long-wavelength excitation is due to the smaller initial separation between oppositely charged thermalized pairs of carriers resulting in smaller dissociation efficiency. Good agreement is also obtained between the measured temperature dependence of the photogeneration efficiency and that predicted by the theory.

Effect of electric fields on the daytime high-latitude E and F regions

Abstract: We have obtained solutions of the coupled continuity, momentum, and energy equations for NO(+), O(+), and O2(+) ions for conditions appropriate to the daytime high-latitude E and F regions. Owing to the rapid increase of the reaction O(+) + N2 yielding NO(+) + N with ion energy, high-latitude electric fields and consequent perpendicular-E x B drifts deplete O(+) in favor of NO(+). For electric field strengths less than about 10 mV/m the depletion of O(+) is small, and the altitude profiles of ion density are similar to those found at mid-latitudes. However, for moderate electric field strengths (50 mV/m), NO(+) is substantially increased in relation to O(+) and becomes an important ion throughout the F region. For large electric fields (200 mV/m), NO(+) completely dominates the ion composition to at least 600 km, decreasing at high altitudes with a diffusive equilibrium scale height. Since the overall F region electron density decreases markedly with increasing electric field strength, it appears that high-latitude, daytime electron density troughs are directly related to the presence of ionospheric electric fields.

Relativistic limitations on runaway electrons

Abstract: The non-relativistic theory of a plasma in an electric field E predicts that there will always be runaway electrons, although their number will be exponentially small for fields less than the Dreicer field ED. However, when E/ED ~ kT/mec2, the ratio of the electron thermal energy to the rest mass energy, relativistic effects become important. After comparing earlier non-relativistic calculations we extend the approach of Kruskal and Bernstein to take account of relativistic effects and also to investigate the influence of impurities. It is found that below the critical electric field ER = ED (kT/mec2) absolutely no runaways are generated. In addition, the number of runaway electrons produced by electric fields in excess of ER is calculated and we find significant modifications to the non-relativistic estimates when (ED/E)2 (kT/mec2) > 1.

High-field transport in wide-band-gap semiconductors

Abstract: The drift velocity in high electric fields is calculated for several wide-band-gap semiconductors. Saturated velocities above ${10}^{7}$ cm/sec are found for several and SiC, diamond, and GaN hold promise for values above 2\ifmmode\times\else\texttimes\fi{}${10}^{7}$ cm/sec.

Computation of the Electromagnetic Fields and Induced Temperatures Within a Model of the Microwave-Irradiated Human Eye

Abstract: The electromagnetic fields within a detailed model of the human eye and its surrounding bony orbit are calculated for two different frequencies of plane-wave irradiation: 750 MHz and 1.5 GHz. The computation is performed with a finite-difference algorithm for the time-dependent Maxwell's equations, carried out to the sinusoidal steady state. The heating potential, derived from the square of the electric field, is used to calculate the temperatures induced within the eyeball of the model. This computation is performed with the implicit alternating-direction (IAD) algorithm for the heat conduction equation. Using an order-of-magnitude estimate of the heat-sinking capacity of the retinal blood supply, it is determined that a hot spot exceeding 40.4/spl deg/C occurs at the center of the model eyeball at an incident power level of 100 mW/cm/sup 2/ at 1.5 GHz.

Threshold energy effect on avalanche breakdown voltage in semiconductor junctions

Abstract: The band bending for avalanche breakdown in semiconductor junctions and its temperature dependence are predicted taking account of threshold energy effects on the ionization process in semiconductors. Where experimental results exist, the theoretical predictions and experimental results are in excellent agreement. In the high electric field region inclusion of both bulk and boundary threshold energy effects is essential. The predictions were based on exact solutions in the nonlocalized ionization coefficient formulation developed by Okuto and Crowell who showed that ionization coefficients as usually understood are functions of both electric field and position in a device. Predictions for abrupt and p - i - n junctions in Ge, Si, GaAs and GaP are presented.

Magnetic merging in a collisionless plasma

Abstract: This paper examines the problem of magnetic merging in a fully collisionless plasma, i.e., a plasma of noninteracting charged particles, explicitly avoiding the fluid (MHD) approximation. The Alfven self-consistency criterion that relates the plasma density to the electric and magnetic fields is shown to be equivalent, when suitably generalized, to the stress-balance requirement discussed by Rich, Vasyliunas, and Wolf. From this criterion the self-consistent electric field and the magnetic merging speed are obtained as functions of the magnetic field configuration and of the incident plasma parameters. The merging speed obtained for equal antiparallel fields is within a factor of 2 of the result of fluid theory if the incident plasma pressure is initially isotropic. The merging speed is respectively reduced or enhanced when the incident parallel plasma pressure P∥ is greater than or less than the incident transverse pressure P⊥. When P∥ - P⊥ = B²/µ0 (the marginal fire hose stability condition), merging ceases. For the more general field configuration wherein the opposing magnetic fields B1 and B2 have arbitrary magnitudes and directions the merging electric field is shown to have a maximum value when the fields are antiparallel and to decrease monotonically to zero as the angular separation of the fields decreases to arccos (B1/B2). The expected merging electric field at the day side magnetopause as a function of the strength and direction of the interplanetary magnetic field is presented in a form that can be compared directly with observations. Although a detailed comparison is not feasible, the general results of the analysis are compatible with available observations in the magnetosphere and solar wind.

Audio-frequency magnetotellurics with a grounded electric dipole source

Abstract: The conventional audio‐frequency magnetotelluric method has been useful in problems of shallow exploration to depths of a few kilometers. Because the natural sources are unpredictable in strength and direction, we have examined the possibility of doing magnetotelluric sounding utilizing the ratio of horizontal electric field to horizontal magnetic field from a controlled source. The source chosen for this study was a grounded electric dipole. The equations for the electric and magnetic fields around this antenna as a function of range and azimuth have been calculated for a half‐space and for a one‐layered earth. These calculations were checked for the half‐space case with an analog model and in the field at the Bonneville Salt Flats. In addition, layered cases were calculated, and a field example near Timmins, Ont., studied. Provided the distance of the observation point from the source is three skin depths (relative to the greatest resistivity in the section) or more, the conventional magnetotelluric int...

Model for the bleaching of WO3 electrochromic films by an electric field

Abstract: Measurements have been made of the current flow in amorphous WO3 films containing electrons and mobile cations. In a configuration in which electrons are extracted at one contact and cations at the other, the current decays as t−3/4 over many decades of time. By using space‐charge current flow ideas, we develop a theory that gives the correct time dependence and magnitude of the current for this double‐extraction phenomenon.

Electrostatic and electromagnetic turbulence associated with the earth's bow shock

Abstract: Simultaneous measurements were made of the electric and magnetic field spectral densities in the earth's bow shock by a plasma wave experiment on the Imp 6 spacecraft. The frequency range of the plasma wave detector was 20 Hz to 200 kHz. Electric fields were measured with high-sensitivity 100-m long dipole antennas and magnetic fields were measured with single-turn loop antennas. Two components are distinguished in the electric field spectrum in the bow shock: one component has a broad peak centered in the region 200-800 Hz, while the other component increases monotonically with decreasing frequency. The magnetic field spectrum has only one component that increases monotonically with decreasing frequency and has an upper cutoff frequency near the local electron gyrofrequency. This magnetic field turbulence is judged to be caused by whistler mode waves. The monotonic component of the electric field spectrum is thought to be the electric field spectrum of these whistler mode waves.

Parity violation induced by weak neutral currents in atomic physics. part II

Abstract: The first part of this paper gives a detailed account of the evaluation of the electric dipole amplitude induced in alkali one-photon S-S transitions, by the parity violating electron-nucleus short range potential Vp.v. associated with the weak neutral currents. Two methods are presented : the first involves an explicit sum over the contributions of the P-states admixed with the S-states and incorporates the best information available on S-P electric dipole amplitudes. The second method, mathematically more elegant, avoids with the help of Green's function techniques any explicit sum over the P states, and, provided that some spin-orbit corrections are neglected, leads to a fairly simple formula involving Coulomb integrals tabulated in the literature and the interpolated quantum defects for S and P waves. The second part is devoted to a description of possible ways to detect parity violation induced in radiative S-S transitions, with a brief discussion of physical processes which could be a source of experimental difficulty. The last section of the paper deals with a theoretical analysis of the influence of a static electric field on the radiative S-S transitions. An evaluation of the induced electric dipole amplitude in the case of cesium indicates that it will compete with the magnetic dipole amplitude for electric fields larger than 10 V/cm. An interference effect between these two amplitudes gives rise to an electronic polarization in the final atomic state proportional to the vector product of the static electric field by the photon momentum which, in a typical case, could be as large as 64 %; the measurement of this interesting and rather peculiar effect will lead to a determination of the sign of the magnetic dipole amplitude. Moreover parity violation could manifest itself by a dependence of this electron polarization on the state of circular polarization of the incident photon.

Spatial aspects of the electric fields generated by weakly electric fish

Abstract: 1. The electric fields of four species of wave type, gymnotid fishes were measured and mapped using a technique that allowed accurate assessment of small electric fields, free of unknown field compression and distortion artifacts. 2. Dipole moment values were calculated for each fish's electric field from measurements made at a sufficient distance (Table 1). A dipole moment is an absolute evaluation of the electric fish's field strength that can be used for quantitative, intraspecific and interspecific comparisons. 3. The electric fish, as a field source, represents a distributed rostral pole and a point-like caudal pole (Fig. 2). Deviations of a fish's electric field from that of a dipole field increase with fish size, decreasing water resistivity, and decreasing distance from the fish. 4. Apteronotid species maintain a constant current electric organ output (dropping less than 5%) in water of resistivity up to 15 kOhm · cm, whereas rhamphichthyid species maintain a constant current output only in water up to 10 kOhm · cm (Fig. 6). Within each family, the larger fish maintained their current output level in higher water resistivities than did smaller fish. 5. Electrocommunication distances for the individual fishes are predicted based upon their measured electric field magnitudes and the known electrosensitivities of these species (Table 2); consequences of the geometry of the fishes' electric fields on object detection and object resolution are discussed.

Hole mobility and transport in thin SiO2 films

Abstract: The first measurement of the hole mobility and its temperature dependence in thermally grown SiO2 on Si is reported and found to follow μ≃20 exp(−0.6eV/kT) cm2/V sec. In agreement with previous studies, the energy required to form an electron−hole pair with ionizing radiation is found to be field dependent and at very high fields is in the range of 18 eV/electron−hole pair, and is nearly temperature independent from 77 to 370 °K.

Chapter 5 – constant electromagnetic fields

Abstract: Publisher Summary This chapter discusses constant electromagnetic fields. For a constant electric field, the Coulomb law states that field produced by a point charge is inversely proportional to the square of the distance from the charge. If there is a system of charges, then the held produced by this system is equal, according to the principle of superposition, to the sum of the fields produced by each of the particles individually. In determining the energy of a system of charges, it is started from the energy of the field, that is, from the expression for the energy density. From the Larmor's theorem, the derivative of average angular momentum (M) of the system is equal to the moment (K) of the forces acting on the system. If the e/m ratio is the same for all particles of the system, the angular momentum and magnetic moment are proportional to one another. The vector M¯ (and with it the magnetic moment m¯) rotates with angular velocity –Ω around the direction of the field, while its absolute magnitude and the angle that it makes with this direction remain fixed.

Electrostatic noise bands associated with the electron gyrofrequency and plasma frequency in the outer magnetosphere

Abstract: Naturally occurring noise bands near the electron plasma frequency are frequently detected by the University of Iowa plasma wave experiment on the Imp 6 satellite in the region from just inside the plasmapause to radial distances of about 10 earth radii in the outer magnetosphere. The electric field strength of these noise bands is usually small with typical broad band electric field strengths of about 2 microvolts per m. A magnetic field has been detected only in a few unusually intense cases, and in these cases the magnetic field energy density is several orders of magnitude smaller than the electric field energy density. The bands are observed at all magnetic latitudes covered by the Imp 6 orbit and appear to be a permanent feature of the outer magnetosphere. They are found at all local times and occur least frequently in the quadrant from 18 to 24 hours. The bands appear to consist of two distinct spectral types called diffuse and narrow band. In both types the center frequency of the noise band is bounded by consecutive harmonics of the electron gyrofrequency, and these noise bands occur most often between harmonics that are near the local electron plasma frequency.

The Dielectric Properties of Nematic 44′ n-pentylcyanobiphenyI

Abstract: The electric permittivity of nematic 44′ n-pentylcyanobiphenyl has been measured in the presence of electric and magnetic fields. Values of the permittivity components for the aligned state have been obtained and analysed in terms of the statistical theory of Maier and Meier. The behaviour of bulk samples of the material in electric and magnetic fields has been investigated, and yielded a mean permittivity for the non-aligned state. The macroscopic behaviour is discussed in terms of the continuum theory. Variable frequency measurements have shown the presence of a dispersion region in e∥ at about 5 MHz.

Lunar electric fields, surface potential and associated plasma sheaths

Abstract: A review is given of studies of the electric-field environment of the moon. Surface electric potentials are reported for the dayside and terminator regions, electron and ion densities in the plasma sheath adjacent to each surface-potential regime are evaluated, and the corresponding Debye lengths are estimated. The electric fields, which are approximated by the surface potential over the Debye length, are shown to be at least three orders of magnitude higher than the pervasive solar-wind electric field and to be confined to within a few tens of meters of the lunar surface.

The local electric field. I. The effect on isotropic and anisotropic Rayleigh scattering

Abstract: Isotropic and anisotropic Rayleigh light scattering intensities are reported for seven liquids. Anisotropic intensities as a function of refractive index for four molecules are also reported. We have used spectral analysis to separate the single molecule scattering from the complicating effects of collisional scattering and static pair correlations. Several macroscopic continuum models for the local electric field at a molecule in a liquid phase are summarized and these theoretical models are compared with our experimental results for scattering from single molecules. We have established the equivalence of the local field correction calculated from a fourth‐power local field with that calculated from the dielectric fluctuation method for all models. We further show that of these local field corrections, only that calculated by the ellipsoidal Onsager–Scholte model is consistent with all our experimental data. The size and shape parameters of these models are related to molecular parameters.

Potential-Dependent Conductances in Lipid Membranes Containing Alamethicin

Abstract: This article is concerned primarily with the mechanism of the potential-dependent conductance induced in artificial lipid membranes by the cyclic polypeptide antibiotic alamethicin. It has already been shown from studies of the fluctuations that can be detected in very small membrane currents, that alamethicin forms transient pores of some 0.6 nm in diameter and that, for small inorganic ions, these are poorly selective. The origin of these pores, their spatial distribution and interaction are discussed. It is demonstrated that the sensitivity of the membrane conductance to the applied potential arises only to a slight extent from the current-voltage relations for the individual pores, and that the main effect stems from the influence of the potential on the frequency of opening of the pores. From the properties of lipid membranes containing alamethicin in a wide variety of electrolytes, and from other evidence, it is concluded that the polypeptide reacts to the electric field more probably because it has a large dipole moment than because it binds ions. It is proposed that the conducting complex is capable of functioning in either of two orientations, and that it is these two possibilities that give rise to certain differences in the single channel characteristics for the two directions of the field.

Charge Carrier Transport Properties of Semiconductor Materials Suitable for Nuclear Radiation Detectors

Abstract: Charge carrier drift velocities in semiconductor materials suitable for solid state detectors has been reviewed. Si, Ge, CdTe and GaAs are considered. New data for HgI2 recently obtained are also reported. The data cover a large range of temperatures (6-430 K) and electric fields up to 50 KV/cm. An anisotropy effect in the drift velocity obtained by applying the electric field parallel to different crystallographic axis is also discussed for the case of Si and Ge.

Is there an electrostatic field tangential to the dayside magnetopause and neutral line

Abstract: Energy considerations are put forward which lead to the conclusion that the magnetopause current does not flow through the magnetospheric potential difference (of 60,000 V), and that the magnetopause is roughly an equipotential surface. Because of the necessary continuity of the tangential component of the electric field, this conclusion implies that no steady-state electric field exists along the neutral line located near the dayside magnetopause (in an open magnetospheric model). Since such an electric field is an essential part of the theory of merging of magnetic lines of force, it is concluded that the merging model does not hold for the electric field.

Observations of an intense field‐aligned thermal ion flow and associated intense narrow band electric field oscillations

Abstract: An investigation is conducted concerning the conditions encountered during a Javelin sounding rocket experiment conducted on Apr. 3, 1970 at Fort Churchill, Canada. Evidence is presented that near the equatorward edge of the auroral arc an intense beam of cold plasma ions was flowing parallel to the earth's magnetic field. The beam was associated with intense narrow band electric field oscillations near the local ion gyrofrequency. The data support the hypothesis that intense electrostatic ion cyclotron waves were driven unstable by field-aligned currents.