Electric current-induced mass flow in very thin infinite metallic films

This paper reports on the mass transport behavior of infinitely extended, continuous, and very thin metallic films under the influence of electric current. Application of direct current of high densities (> 10(8) A/m(2)) results in visible melting of thin film at only one of the electrodes, and the melt then flows towards the other electrode in a circularly symmetric fashion forming a microscale ring pattern. For the two tested thin film systems, namely Cr and Al, of thicknesses ranging from 4 to 20 nm, the above directional flow consistently occurred from cathode to anode and anode to cathode, respectively. Furthermore, application of alternating electric current results in flow of the liquid material from both the electrodes. The dependence of critical flow behavior parameters, such as flow direction, flow velocity, and evolution of the ring diameter, are experimentally determined. Analytical models based on the principles of electromigration in liquid-phase materials are developed to explain the experimental observations.

A general design method for electric machines using magnetic circuit model considering the flux saturation problem

This paper proposes an analytical approach that is generalized for the design of various types of electric machines based on a physical magnetic circuit model. Conventional approaches have been used to predict the behavior of electric machines but have limitations in accurate flux saturation analysis and hence machine dimensioning at the initial design stage. In particular, magnetic saturation is generally ignored or compensated by correction factors in simplified models since it is difficult to determine the flux in each stator tooth for machines with any slot-pole combinations. In this paper, the flux produced by stator winding currents can be calculated accurately and rapidly for each stator tooth using the developed model, taking saturation into account. This aids machine dimensioning without the need for a computationally expensive finite element analysis (FEA). A 48-slot machine operated in induction and doubly-fed modes is used to demonstrate the proposed model. FEA is employed for verification.

Explorations of electric-current system in solar active regions .1. Empirical inferences of the current flows

In this paper we explore techniques to identify sources of electric current systems and their channels of flow in solar active regions. Measured photospheric vector magnetic fields (VMF) together with high-resolution white-light and H filtergrams provide the data base to derive the current systems in the photosphere and chromosphere. Simple mathematical constructions of fields and currents are also adopted to understand these data. As an example, the techniques are then applied to infer current systems in AR 2372 in early April 1980. The main results are: (i) In unipolar sunspots the current density may reach values of 103 CGSE, and the Lorentz force on it can accelerate the Evershed flow, (ii) Spots exhibiting significant spiral pattrn in the penumbral filaments are the sources of vertical major currents at the photospheric surface, (iii) Magnetic neutral lines where the transverse field was strongly sheared were channels along which strong current system flows, (iv) The inferred current systems produced oppositely-flowing currents in the area of the delta configuration that was the site of flaring in AR 2372.

Part I. Electric birefringence studies of deoxyribonucleic acids. Part II. Selective dissociation of nucleohistone complexes

Part I

The electric birefringence of dilute DNA solutions has been studied in considerable detail and on a large number of samples, but no new and reliable information was discovered concerning the tertiary structure of DNA. The large number of variables which effect the birefringence results is discussed and suggestions are made for further work on the subject.

The DNA molecules have been aligned in a rapidly alternating (10 to 20 kc/sec) square wave field confirming that the orientation mechanism is that of counterion polarization. A simple empirical relation between the steady state birefringence, Δn_st, and the square of the electric field, E, has been found: Δn_st = E²/(a E² + b), where a = 1/Δn_s and b = (E²/Δn_st)_E→o. Δn_s is the birefringence extrapolated to infinite field strength.

The molecules show a distribution of relaxation times from 10^-4 to 0.2 sec, which is consistent with expectations for flexible coil molecules. The birefringence and the relaxation times decrease with increasing salt concentrations. They also depend on the field strength and pulse duration in a rather non-reproducible manner, which may be due in part to changes in the composition of the solution or in the molecular structure of the DNA (other than denaturation). Further progress depends on the development of some control over these effects.

Part II

The specificity of the dissociation of reconstituted and native deoxyribonucleohistones (DNH) by monovalent salt solutions has been investigated. A novel zone ultracentrifugation method is used in which the DNH is sedimented as a zone through a preformed salt gradient, superimposed on a stabilizing D₂O (sucrose) density gradient. The results, obtained by scanning the quartz sedimentation tubes in a spectrophotometer, were verified by the conventional, preparative sedimentation technique. Procedures are discussed for the detection of microgram quantities of histones, since low concentrations must be used to prevent excessive aggregation of the DNH.

The data show that major histone fractions are selectively dissociated from DNH by increasing salt concentrations: Lysine rich histone (H I) dissociates gradually between 0.1 and 0.3 F, slightly lysine rich histone (H II) dissociates as a narrow band between 0.35 and 0.5 F, and arginine rich histone (H III, H IV) dissociates gradually above 0.5 F NaClO₄.

The activity of the partially dissociated, native DNH in sustaining RNA synthesis, their mobility and their unusual heat denaturation and renaturation behavior are described. The two-step melting behavior of the material indicates that the histones are non-randomly distributed along the DNA, but the implications are that the uncovered regions are not of gene-size length.

The experiment to evaluate the AC loss of 2G HTS windings in the application of rotating electric machines

This paper presents the design of an AC loss experiment using nitrogen boil-off method. This experiment is aimed at exploring the AC loss of HTS double race-track coils which will be installed on the rotor of a wind turbine generator. The operating environment is simulated by designing a cryostat with rotating magnetic field windings. Apart from the fact that the alternating magnetic field causes most of AC loss on the HTS coils, we also believe that the DC background field would be another important factor causing AC loss if the HTS coil is experiencing by both alternating magnetic field in the perpendicular direction and DC background field in the parallel direction. In order to perform the boil-off measurement, we present the method to estimate the heat leakage in the cryostat which might cause errors to the measurement. © 2011 IEEE.

Superhydrophobic carbon nanotube electrode produces a near-symmetrical alternating current from photosynthetic protein-based photoelectrochemical cells

The construction of protein-based photoelectrochemical cells that produce a variety of alternating currents in response to discontinuous illumination is reported. The photovoltaic component is a protein complex from the purple photosynthetic bacterium Rhodobacter sphaeroides which catalyses photochemical charge separation with a high quantum yield. Photoelectrochemical cells formed from this protein, a mobile redox mediator and a counter electrode formed from cobalt disilicide, titanium nitride, platinum, or multi-walled carbon nanotubes (MWCNT) generate a direct current during continuous illumination and an alternating current with different characteristics during discontinuous illumination. In particular, the use of superhydrophobic MWCNT as the back electrode results in a near symmetrical forward and reverse current upon light on and light off, respectively. The symmetry of the AC output of these cells is correlated with the wettability of the counter electrode. Potential applications of a hybrid biological/synthetic solar cell capable of generating an approximately symmetrical alternating current are discussed. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theory of terahertz-photocurrent resonances in miniband superlattices

The currents of de and ac components and their phase-angle cosines for a superlattice under a direct bias and alternating field are calculated with the balance equations. It is found that the de currents as functions of the direct field show resonance peaks at the fields corresponding to the Bloch frequency equal to n omega. With increasing alternating field intensity the resonance peaks of higher harmonic increase, and simultaneously the first peak caused by the de field decreases. The results are in good agreement with the experimental results, indicating that this resonance can be understood in terms of electron acceleration within the miniband, i.e., it is a bulk superlattice effect, rather than caused by the electric-field localization mechanism (Wannier Stark ladder). The phase-angle cosine for the first harmonic cos phi(1) becomes negative when the Bloch frequency increases to be larger than the frequency of the ac field omega, and it also shows resonance peaks at the resonance frequencies n omega. The negative cos phi(1) may cause the energy transferred to the alternating field, i.e., oscillation of the system.

Polarization switching current of vertical cavity surface-emitting Lasers in an applied electric field

The polarization of vertical-cavity surface-emitting laser (VCSEL) can be controlled by electro-optic birefringence. We calculated the birefringence resulted from external electric field which was imposed on the top DBR of VCSEL by assuming that the two polarization modes were in the same place of the gain spectra in the absence of electric field beginning. By modifying SFM, the affection of the electric field strength on the polarization switching currents between the two polarization modes had been shown.

Higher order response of nonlinear composite in external AC electric field

The fifth-order effective nonlinear responses at fundament frequency and higher-order harmonics are given for nonlinear composites, which obey a current-field relation of the form J = sigmaE + x\E\(2) E, if a sinusoidal alternating current (AC) external field with finite frequency omega is applied. As two examples, we have investigated the cylinder and spherical inclusion embedded in a host and, for larger volume fraction, also derived the formulae of effective nonlinear responses at higher-order harmonics by the aid of the general effective response definition. Furthermore, the relationships between effective nonlinear responses at harmonics are given. (C) 2003 Elsevier Science B.V. All rights reserved.

Effective response of a non-linear composite in external AC electric field

A general effective response is proposed for nonlinear composite media, which obey a current field relation of the form J = sigmaE + chi\E\(2) E when an external alternating current (AC) electrical field is applied. For a sinusoidal applied field with finite frequency omega, the effective constitutive relation between the current density and electric field can be defined as, = sigma(e) + chi(e) <\E(x, omega, t)\(2) E(x, omega, t)> + (. . .), where sigma(e) and chi(e) are the general effective linear and nonlinear conductive responses, respectively. The angled brackets <(. . .)> denotes the ensemble average. As two examples, we have investigated the cylindrical and spherical inclusions embedded in a host and also derived the formulae of the general effective linear and nonlinear conductive responses in dilute limit. For higher volume fraction of inclusions, we have proposed a nonlinear effective medium approximation (EMA) method to estimate the general effective response of nonlinear composites in external AC field. Furthermore, the effective nonlinear responses at harmonics are predicted by using the general effective response. (C) 2002 Elsevier Science B.V. All rights reserved.

Impulsive electric fields driven by high-intensity interactions

The interaction of high-intensity laser pulses with matter releases instantaneously ultra-large currents of highly energetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiments in which such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channeling in underdense plasmas have been studied in this way, as also the processes of Debye sheath formation and MeV ion front expansion at the rear of laser-irradiated thin metallic foils. Laser-driven impulsive fields at the surface of solid targets can be applied for energy-selective ion beam focusing.

Electrode field penetration: A new interpretation of tunneling currents in barium strontium titanate (BST) thin films

This paper shows that penetration of the applied electric field into the electrodes of a ferroelectric thin film capacitor produces both an interfacial capacitance and an effective mechanism for electron tunneling. The model predictions are compared with experimental results on Au-BST-SrRuO3 capacitors of varying thicknesses, and the agreement is excellent.

Polarization retention loss in PbTiO3 ferroelectric films due to leakage currents

The relationship between retention loss in single crystal PbTiO3 ferroelectric thin films and leakage currents is demonstrated by piezoresponse and conductive atomic force microscopy measurements. It was found that the polarization reversal in the absence of an electric field followed a stretched exponential behavior 1-exp[-(t/k)(d)] with exponent d>1, which is distinct from a dispersive random walk process with d <. The latter has been observed in polycrystalline films for which retention loss was associated with grain boundaries. The leakage current indicates power law scaling at short length scales, which strongly depends on the applied electric field. Additional information of the microstructure, which contributes to an explanation of the presence of leakage currents, is presented with high resolution transmission electron microscopy analysis.

Letter - Frederic Nicholls (Canadian General Electric) to W.B. Rankine, 17 December 1897

A letter from 2nd Vice President and General Manager of Canadian General Electric Company, Frederic Nicholls to W. B. Rankine regarding a bid for contract. The letter mentions that the bid for two alternating generators for the Canadian side of Niagara Falls was won by Westinghouse Eletric and Manufacturing Co. Nicholls also mentions that there will be other opportunites to win contracts as more machines are required. Nicholls also implies that Westinghouse may have bid under cost in an effort to secure the first of many contracts with the Canadian Niagara Power Company.

An overview of Earth's global electric circuit and atmospheric conductivity

The Earth’s global atmospheric electric circuit depends on the upper and lower atmospheric boundaries formed by the ionosphere and the planetary surface. Thunderstorms and electrified rain clouds drive a DC current (∼1 kA) around the circuit, with the current carried by molecular cluster ions; lightning phenomena drive the AC global circuit. The Earth’s near-surface conductivity ranges from 10−7 S m−1 (for poorly conducting rocks) to 10−2 S m−1 (for clay or wet limestone), with a mean value of 3.2 S m−1 for the ocean. Air conductivity inside a thundercloud, and in fair weather regions, depends on location (especially geomagnetic latitude), aerosol pollution and height, and varies from ∼10−14 S m−1 just above the surface to 10−7 S m−1 in the ionosphere at ∼80 km altitude. Ionospheric conductivity is a tensor quantity due to the geomagnetic field, and is determined by parameters such as electron density and electron–neutral particle collision frequency. In the current source regions, point discharge (coronal) currents play an important role below electrified clouds; the solar wind-magnetosphere dynamo and the unipolar dynamo due to the terrestrial rotating dipole moment also apply atmospheric potential differences. Detailed measurements made near the Earth’s surface show that Ohm’s law relates the vertical electric field and current density to air conductivity. Stratospheric balloon measurements launched from Antarctica confirm that the downward current density is ∼1 pA m−2 under fair weather conditions. Fortuitously, a Solar Energetic Particle (SEP) event arrived at Earth during one such balloon flight, changing the observed atmospheric conductivity and electric fields markedly. Recent modelling considers lightning discharge effects on the ionosphere’s electric potential (∼+250 kV with respect to the Earth’s surface) and hence on the fair weather potential gradient (typically ∼130 V m−1 close to the Earth’s surface. We conclude that cloud-to-ground (CG) lightning discharges make only a small contribution to the ionospheric potential, and that sprites (namely, upward lightning above energetic thunderstorms) only affect the global circuit in a miniscule way. We also investigate the effects of mesoscale convective systems on the global circuit.