Showing papers on "Electric field published in 1997"
TL;DR: In this paper, first-order changes of wave functions and density with respect to small atomic displacements or infinitesimal homogeneous electric fields within the density-functional theory are studied.
Abstract: Starting from the knowledge of first-order changes of wave functions and density with respect to small atomic displacements or infinitesimal homogeneous electric fields within the density-functional theory, we write the expressions for the diagonal or mixed second-order derivatives of the total energy with respect to these perturbations: dynamical matrices for different wave vectors, Born effective-charge tensors and electronic dielectric permittivity tensors. Interatomic force constants and the phonon-band structure are then obtained by computing the Fourier transform of dynamical matrices on a regular mesh of wave vectors, with an eventual, separate treatment of the long-range dipole-dipole interaction. The same ingredients also allow one to compute the low-frequency response of the crystal to homogeneous electric fields.
2,378 citations
TL;DR: In this article, the authors proposed a method for optical trapping and alignment of dielectric particles in aqueous environments at the nanometer scale based on the highly enhanced electric field close to a laser-illuminated metal tip and the strong mechanical forces and torque associated with these fields.
Abstract: We propose a scheme for optical trapping and alignment of dielectric particles in aqueous environments at the nanometer scale. The scheme is based on the highly enhanced electric field close to a laser-illuminated metal tip and the strong mechanical forces and torque associated with these fields. We obtain a rigorous solution of Maxwell’s equations for the electromagnetic fields near the tip and calculate the trapping potentials for a dielectric particle beyond the Rayleigh approximation. The results indicate the feasibility of the scheme. [S0031-9007(97)03687-9] Optical trapping by highly focused laser beams has been extensively used for the manipulation of submicronsize particles and biological structures [1]. Conventional optical tweezers rely on the field gradients near the focus of a laser beam which give rise to a trapping force towards the focus. The trapping volume of these tweezers is diffraction limited. Near-field optical microscopy enables the optical measurements at dimensions beyond the diffraction limit and makes it possible to optically monitor dynamics of single biomolecules [2]. The potential application of optical near fields to manipulate atoms or nanoparticles has been discussed in Ref. [3]. In this Letter, we present a new methodology for calculating rigorously and self-consistently the trapping forces acting on a nanometric particle in the optical near field and propose a novel high-resolution trapping scheme. The proposed nanometric optical tweezers rely on the strongly enhanced electric field at a sharply pointed metal tip under laser illumination. The near field close to the tip mainly consists of evanescent components which decay rapidly with distance from the tip. The utilization of the metal tip for optical trapping offers the following advantages: (1) The highly confined evanescent fields significantly reduce the trapping volume; (2) the large field gradients result in a larger trapping force; and (3) the field enhancement allows the reduction of illumination power and radiation damages to the sample. High resolution surface modification based on the field enhancement at laser-illuminated metal tips has been recently demonstrated [4]. It is essential to perform a rigorous electromagnetic analysis to understand the underlying mechanism for the field enhancement. Our analysis is therefore relevant not only to optical tweezers, but also to other applications, such as surface modification, nonlinear spectroscopy and near-field optical imaging. To solve Maxwell’s equations in the specific geometry of the tip and its environment, we employ the multiple multipole method (MMP) which recently has been applied to various near-field optical problems [5]. In MMP, electromagnetic fields are represented by a series expansion of known analytical solutions of Maxwell’s equations. To determine the unknown coefficients in the series expansion, boundary conditions are imposed at discrete points on the interfaces between adjacent homogeneous domains. Once the resulting system of equations is solved and the coefficients are determined, the solution is represented by a self-consistent analytical expression. Figure 1 shows our three dimensional MMP simulation of the foremost part of a gold tip (5 nm tip radius) in water for two different monochromatic plane-wave excitations. The wavelength of the illuminating light is l › 810 nm (Ti:sapphire laser), which does not match the surface plasmon resonance. The dielectric constants of tip and water were taken to be « › 224.9 1 1.57i and « › 1.77, respectively [6]. In Fig. 1(a), a plane wave is incident from the bottom with the polarization perpendicular to the tip axis, whereas in Fig. 1( b) the tip is illuminated from the side with the polarization parallel to the tip axis. A striking difference is seen for the two different polarizations: in Fig. 1( b), the intensity
984 citations
TL;DR: In this paper, it was shown that the switching of resistive states in manganites can be achieved not only by a magnetic field, but also by an electric field for manganite oxides of the form Pr1−xCaxMnO3.
Abstract: Magnetoresistive devices (based on, for example, magnetic multilayers1) exhibit large changes in electrical resistance in response to a magnetic field, which has led to dramatic improvements in the data density and reading speed of magnetic recording systems Manganese oxides having a perovskite structure (the so-called manganites) can exhibit a magnetoresistive response that is many orders of magnitude larger than that found for other materials, and there is therefore hope that these compounds might similarly be exploited for recording applications2,3,4,5,6,7,8,9,10,11 Here we show that the switching of resistive states in the manganites can be achieved not only by a magnetic field, but also by an electric field For manganites of the form Pr1−xCaxMnO3, we find that an electrical current (and by implication a static electric field) triggers the collapse of the low-temperature, electrically insulating charge-ordered state to a metallic ferromagnetic state We suggest that such a phenomenon could be exploited to pattern conducting ferromagnetic domains within an insulating antiferromagnetic matrix, and so provide a route for fabricating micrometre- or nanometre-scale electromagnets
930 citations
TL;DR: In this article, the changes in density, wave functions, and self-consistent potentials of solids, in response to small atomic displacements or infinitesimal homogeneous electric fields, are considered in the framework of the density-functional theory.
Abstract: The changes in density, wave functions, and self-consistent potentials of solids, in response to small atomic displacements or infinitesimal homogeneous electric fields, are considered in the framework of the density-functional theory. A variational: principle for second-order derivatives of the energy provides a basis for efficient algorithmic approaches to these linear responses, such as the state-by-state conjugate-gradient algorithm presented here in detail. The phase of incommensurate perturbations of periodic systems, that are, like phonons, characterized by some wave vector, can be factorized: the incommensurate problem is mapped on an equivalent one presenting the periodicity of the unperturbed ground state. The singularity of the potential change associated with an homogeneous field is treated by the long-wave method. The efficient implementation of these theoretical ideas using plane waves, separable pseudopotentials, and a nonlinear exchange-correlation core correction is described in detail, as well as other technical issues.
860 citations
TL;DR: In this paper, the quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied, and the electric field dependence of the single-dot spectrum is characterized by a highly polarizable excited state (∼10 5 cubic angstroms, compared to typical molecular values of order 10 to 100 cubic angramss), in the presence of randomly oriented local electric fields that change over time.
Abstract: The quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied. The electric field dependence of the single-dot spectrum is characterized by a highly polarizable excited state (∼10 5 cubic angstroms, compared to typical molecular values of order 10 to 100 cubic angstroms), in the presence of randomly oriented local electric fields that change over time. These local fields result in spontaneous spectral diffusion and contribute to ensemble inhomogeneous broadening. Stark shifts of the lowest excited state more than two orders of magnitude larger than the linewidth were observed, suggesting the potential use of these dots in electro-optic modulation devices.
795 citations
TL;DR: In this article, the authors review the phenonomena which occur in multiphoton physics when the electric field of the applied laser radiation becomes comparable with the Coulomb field strength seen by an electron in the ground state of atomic hydrogen.
Abstract: We review the phenonomena which occur in multiphoton physics when the electric field of the applied laser radiation becomes comparable with the Coulomb field strength seen by an electron in the ground state of atomic hydrogen. This field is reached at an irradiance of approximately . The normal perturbative photon-by-photon based picture of the interaction of individual electrons with the field is replaced by a tunnelling picture in which, in a time of the order of, or less than one optical cycle, atomic wavepackets are generated which escape the confining Coulomb potential. These wavepackets are strongly influenced by the laser, `quiver' and may be accelerated back to the parent ion in a recollision process. Phase-coherent effects locked to the laser field become important: high harmonics are generated from these recollisions. We discuss the theory of such effects, and review progress in understanding how this quiver motion can be coherently controlled. We discuss ionization dynamics and review mechanisms by which atoms may be stabilized in very strong fields. Finally, we discuss relativistic effects which occur at very high-intensities.
643 citations
TL;DR: In this article, a theory for the development of the first streamer when a positive voltage is abruptly applied to a point in air at atmospheric pressure is presented, where the continuity equations for electrons, positive ions and negative ions including the effects of ionization, attachment, recombination, electron diffusion, and photoionization are solved simultaneously with Poisson's equation.
Abstract: A theory is presented for the development of the first streamer when a positive voltage is abruptly applied to a point in air at atmospheric pressure. The continuity equations for electrons, positive ions and negative ions, including the effects of ionization, attachment, recombination, electron diffusion, and photoionization, are solved simultaneously with Poisson's equation. With an applied voltage of 20 kV across a 50 mm gap, the streamer does not reach the cathode. An intense electric field front propagates away from the point into the gap to a distance of 35 mm in 200 ns. During the next the streamer only moves a further 2 mm into the gap, and the electric field at the head of the streamer collapses. Finally, only positive space charge remains which moves away from the point, allowing the field near the point to recover after ; free electrons can thus give rise to a secondary discharge near the anode. The electric field distribution is shown to be quite different from that found previously for in that the electric field in the column of the streamer is generally only a fraction of the critical field for which ionization equals attachment. Streamers for a given applied voltage have a far greater range in air than in . The results presented for air also apply to flue gas mixtures, since the important material properties of both gases are very similar.
528 citations
TL;DR: It is demonstrated that controlled electric fields can be used to regulate transport, concentration, hybridization, and denaturation of single- and double-stranded oligonucleotides and single base pair mismatch discrimination is carried out rapidly and with high resolution.
Abstract: We have demonstrated that controlled electric fields can be used to regulate transport, concentration, hybridization, and denaturation of single- and double-stranded oligonucleotides. Discrimination among oligonucleotide hybrids with widely varying binding strengths may be attained by simple adjustment of the electric field strength. When this approach is used, electric field denaturation control allows single base pair mismatch discrimination to be carried out rapidly (<15 sec) and with high resolution. Electric field denaturation takes place at temperatures well below the melting point of the hybrids, and it may constitute a novel mechanism of DNA denaturation.
523 citations
TL;DR: In this article, the authors examined the kinetics and mechanism of local oxidation of silicon and how factors such as the strength of the electric field, ambient humidity, and thickness of the oxide affect its rate and resolution.
Abstract: Atomic force microscope induced local oxidation of silicon is a process with a strong potential for use in proximal probe nanofabrication. Here we examine its kinetics and mechanism and how such factors as the strength of the electric field, ambient humidity, and thickness of the oxide affect its rate and resolution. Detection of electrochemical currents proves the anodization character of the process. Initial very fast oxidation rates are shown to slow down dramatically as a result of a self-limiting behavior resulting from the build up of stress and a reduction of the electric field strength. The lateral resolution is determined by the defocusing of the electric field in a condensed water film whose extent is a function of ambient humidity.
441 citations
TL;DR: In this article, a hole to electron ionization coefficient ratio of up to 50 was observed for 4H SiC. This was attributed to the discontinuity of the conduction band for the direction along the c axis.
Abstract: Epitaxial p-n diodes in 4H SiC are fabricated showing a good uniformity of avalanche multiplication and breakdown. Peripheral breakdown is overcome using the positive angle beveling technique. Photomultiplication measurements were performed to determine electron and hole ionization rates. For the electric field parallel to the c-axis impact ionization is strongly dominated by holes. A hole to electron ionization coefficient ratio of up to 50 is observed. It is attributed to the discontinuity of the conduction band of 4H SiC for the direction along the c axis. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained.
394 citations
TL;DR: In this paper, the authors studied the attributes of electron field emission from disordered matrix arrays of carbon nanotubes and found that the emission characteristics are quite reproducible in spite of the disorder, density, and quality variations from sample to sample.
Abstract: The attributes of electron field emission from disordered matrix arrays of carbon nanotubes are studied and found to be quite reproducible in spite of the disorder, density, and quality variations from sample to sample. At low applied electric fields, the electron field emission current-voltage characteristics qualitatively follow conventional Fowler-Nordheim behavior up to a critical current density. However, the current rise at low applied fields is anomalously steep, suggesting that the Fowler-Nordheim model is not sufficient to quantitatively characterize the emission. In the high-field region, the emission characteristics have a more complex behavior. In that regime, the instantaneous field emission is reminiscent of the low-field behavior, but discrete switching events lead to an overall current suppression. We attribute the sudden and well-defined onset of the switching events to interactions between neighboring nanotube tips. By correlating the switching behavior to the current-voltage characteristics, we rule out other physical processes that cause similar effects.
TL;DR: In this article, the authors present a unified device model for single layer organic light emitting diodes (LEDs) which includes charge injection, transport, and space charge effects in the organic material.
Abstract: We present a unified device model for single layer organic light emitting diodes (LEDs) which includes charge injection, transport, and space charge effects in the organic material The model can describe both injection limited and space charge limited current flow and the transition between them We specifically considered cases in which the energy barrier to injection of electrons is much larger than that for holes so that holes dominate the current flow in the device Charge injection into the organic material occurs by thermionic emission and by tunneling For Schottky energy barriers less than about 03–04 eV, for typical organic LED device parameters, the current flow is space charge limited and the electric field in the structure is highly nonuniform For larger energy barriers the current flow is injection limited In the injection limited regime, the net injected charge is relatively small, the electric field is nearly uniform, and space charge effects are not important At smaller bias in the injection limited regime, thermionic emission is the dominant injection mechanism For this case the thermionic emissioninjection current and a backward flowing interface recombination current, which is the time reversed process of thermionic emission, combine to establish a quasi-equilibrium carrier density The quasi-equilibrium density is bias dependent because of image force lowering of the injection barrier The net device current is determined by the drift of these carriers in the nearly constant electric field The net device current is much smaller than either the thermionic emission or interface recombination current which nearly cancel At higher bias, injection is dominated by tunneling The bias at which tunneling exceeds thermionic emission depends on the size of the Schottky energy barrier When tunneling is the dominant injection mechanism, a combination of tunnelinginjection current and the backflowing interface recombination current combine to establish the carrier density We compare the model results with experimental measurements on devices fabricated using the electroluminescent conjugated polymer poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] which by changing the contacts can show either injection limited behavior or space charge limited behavior
TL;DR: In this article, a field electron emitter from hollow, open-ended carbon nanotubes has been made, which can emit electrons by tunnelling effects in electric fields, with their small size, small energy spread, high current density and no requirement for heat.
Abstract: Electron guns are indispensable devices that are widely used in household and industrial appliances. Field electron-emitting sources (which emit electrons by tunnelling effects in electric fields), with their small size, small energy spread, high current density and no requirement for heat, have distinct advantages over thermionic emitters. We have made a field electron emitter from hollow, open-ended carbon nanotubes.
TL;DR: Evidence suggests that the long-ranged attraction between particles which causes aggregation is mediated by electric-field-induced fluid flow, and an axially symmetric flow field is imaged around individual particles on a uniform electrode surface.
Abstract: Suspensions of colloidal particles form a variety of ordered planar structures at an interface in response to an a.c. or d.c. electric field applied normal to the interface1–3. This field-induced pattern formation can be useful, for example, in the processing of materials. Here we explore the origin of the ordering phenomenon. We present evidence suggesting that the long-ranged attraction between particles which causes aggregation is mediated by electric-field-induced fluid flow. We have imaged an axially symmetric flow field around individual particles on a uniform electrode surface. The flow is induced by distortions in the applied electric field owing to inhomogeneities in the 'double layer' of ions and counterions at the electrode surface. The beads themselves can create these inhomogeneities, or alternatively, we can modify the electrode surfaces by lithographic patterning so as to introduce specified patterns into the aggregated structures.
TL;DR: In this paper, the shape of the liquid cone and jet, the electric fields in and outside the cone, and the surface charge density at the liquid surface were calculated and compared to the droplet size scaling laws.
TL;DR: The SETSE has been used to image and measure depleted regions, local capacitance, band bending, and contact potentials at submicrometer length scales on the surface of this semiconductor sample.
Abstract: A single-electron transistor scanning electrometer (SETSE)—a scanned probe microscope capable of mapping static electric fields and charges with 100-nanometer spatial resolution and a charge sensitivity of a small fraction of an electron—has been developed. The active sensing element of the SETSE, a single-electron transistor fabricated at the end of a sharp glass tip, is scanned in close proximity across the sample surface. Images of the surface electric fields of a GaAs/AlxGa1−xAs heterostructure sample show individual photo-ionized charge sites and fluctuations in the dopant and surface-charge distribution on a length scale of 100 nanometers. The SETSE has been used to image and measure depleted regions, local capacitance, band bending, and contact potentials at submicrometer length scales on the surface of this semiconductor sample.
TL;DR: The study showed that variations of membrane conductivity, cytoplasmic conductivity and cell radius within the ranges of their physiological values do not influence induced transmembrane voltage substantially, provided that extracellular conductivity also corresponds to the physiological conditions, and duration of the electric pulse is in range of 10μ s or longer.
TL;DR: In this article, it was shown that both reversible and irreversible components of the permittivity decrease linearly with the logarithm of the frequency of the ac field, and that the models describing the interaction of domain walls and randomly distributed pinning centers in magnetic materials can be extended to the displacement of domain wall in ferroelectric thin films.
Abstract: Through the use of relations analogous to that of the Rayleigh law, it is demonstrated that the ac electric field dependence of the permittivity of ferroelectric thin films can be described. It is further shown that both reversible and irreversible components of the permittivity decrease linearly with the logarithm of the frequency of the ac field. The results demonstrate that the models describing the interaction of domain walls and randomly distributed pinning centers in magnetic materials can be extended to the displacement of domain walls in ferroelectric thin films.
TL;DR: In this article, a new approach to self-potential (SP) data interpretation for the recognition of a buried causative SP source system is presented, which is characterized by the presence of primary electric sources or sinks, located within any complex resistivity structure with a flat air-earth boundary.
Abstract: A new approach to self-potential (SP) data interpretation for the recognition of a buried causative SP source system is presented. The general model considered is characterized by the presence of primary electric sources or sinks, located within any complex resistivity structure with a flat air-earth boundary. First, using physical considerations of the nature of the electric potential generated by any arbitrary distribution of primary source charges and the related secondary induced charges over the buried resistivity discontinuity planes, a general formula is derived for the potential and the electric field component along any fixed direction on the ground surface. The total effect is written as a sum of elementary contributions, all of the same simple mathematical form. It is then demonstrated that the total electric power associated with the standing natural electric field component can be written in the space domain as a sum of cross-correlation integrals between the observed component of the total electric field and the component of the field due to each single constitutive elementary charge. By means of the cross-correlation bounding inequality, the concept of a scanning function is introduced as the key to the new interpretation procedure. In the space domain, the scanning function is the unit strength electric field component generated by an elementary positive charge. Next, the concept of charge occurrence probability is introduced as a suitable function for the tomographic imaging of the charge distribution geometry underground. This function is defined as the cross-correlation product of the total observed electric field component and the scanning function, divided by the square root of the product of the respective variances. Using this physical scheme, the tomographic procedure is described. It consists of scanning the section, through any SP survey profile, by the unit strength elementary charge, which is given a regular grid of space coordinates within the section, at each point of which the charge occurrence probability function is calculated. The complete set of calculated grid values can be used to draw contour lines in order to single out the zones of highest probability of concentrations of polarized, primary and secondary electric charges. An extension to the wavenumber domain and to three-dimensional tomography is also presented and discussed. A few simple synthetic examples are given to demonstrate the resolution power of the new SP inversion procedure.
TL;DR: The Polar Satellite carries the first three-axis electric field detector flown in the magnetosphere as mentioned in this paper, which has revealed new classes and features of electric field structures associated with the plasma acceleration that produces discrete auroras and that populates the magnetic field with plasma of ionospheric origin.
Abstract: The Polar Satellite carries the first three-axis electric field detector flown in the magnetosphere. Its direct measurement of electric field components perpendicular and parallel to the local magnetic field has revealed new classes and features of electric field structures associated with the plasma acceleration that produces discrete auroras and that populates the magnetosphere with plasma of ionospheric origin. These structures, associated with the hydrogen ion cyclotron mode, include very large solitary waves, spiky field structures, wave envelopes of parallel electric fields, and very large amplitude, nonlinear, coherent ion cyclotron waves. {copyright} {ital 1997} {ital The American Physical Society}
Patent•
12 Mar 1997TL;DR: The electric field steering assembly as mentioned in this paper is used to control the size and/or location of an electric field in a living organism by adjusting the current and voltage at each anode in response to changes in electrode impedance.
Abstract: The electric field steering assembly is used to control the size and/or location of, and/or steer the position of, an electric field in a living creature. The assembly comprises a pulse generator or stimulator, at least one implanted lead coupled to the stimulator and having, at a distal end thereof, at least three spaced apart electrodes, and electrical circuitry for adjusting the current and/or voltage at each electrode. The electrical circuitry is programmed to: 1) electronically change the size and/or location of an electric field established between the electrodes by independently programming the current flowing through of one or more anode (+) electrode(s) from one or more cathode (-) electrode(s), thereby steering the size and location of the electric field to recruit only target certain tissue and exclude unwanted tissue; and, 2) automatically change the voltage amplitude at each anode in response to changes in electrode impedance in order to maintain a constant anodic current, thereby preserving, for the duration of the therapy, the original electric field found to be effective at implant time.
TL;DR: In this article, two sets of basis functions in spherical coordinates are presented, in terms of which any given ionospheric current system, consisting of horizontal sheet currents and their accompanying field-aligned currents, can be expanded, regardless of any considerations on the ionosphere conductances or the electric field.
Abstract: Two sets of basis functions in spherical coordinates are presented, in terms of which any given ionospheric current system, consisting of horizontal sheet currents and their accompanying field-aligned currents, can be expanded, regardless of any considerations on the ionospheric conductances or the electric field. The single basis functions are called elementary current systems. One basis function set is curl-free and poloidal, and causes a toroidal magnetic field that is restricted to the area above the ionosphere. The other one is divergence-free and toroidal, and causes a poloidal magnetic field which is solely responsible for the magnetic effect of ionospheric currents below the ionosphere. The field-aligned currents are assumed to flow radially. The expansion presented is used on a model of a Cowling channel to decompose its Hall and Pedersen currents into their total divergence-free and curl-free parts. This application example shows how the analysis technique based on the elementary current expansion resolves the physically relevant primary and secondary currents inside the Cowling channel.
TL;DR: In this article, a detailed kinetic model is used to investigate the mechanisms for ionization, dissociation and atomic reassociation in a low-pressure positive column, based on the selfconsistent solutions to the electron Boltzmann equation coupled to a system of rate balance equations for the levels, the electronically excited states of and the and ions.
Abstract: A detailed kinetic model is used to investigate the mechanisms for ionization, dissociation and atomic re-association in a low-pressure positive column. The approach is based on the self-consistent solutions to the electron Boltzmann equation coupled to a system of rate balance equations for the levels, the electronically excited states of and the and ions. The maintenance electric field is self-consistently determined from the continuity equations for electrons and ions. The model provides a satisfactory explanation of measurements conducted in these conditions, in the range p = 0.6 - 2.5 Torr and I = 10 - 100 mA, for the reduced electric field and the concentrations of N atoms and and states. The rate coefficients and are derived here for the two reactions leading to associative ionization by collisions between electronic metastables and , respectively. The dissociation due to the vibration - vibration (V - V) and vibration - translation (V - T) energy exchanges is shown to represent only a minor contribution for the total rate of dissociation, in opposition to previous studies, due to the effects of fast V - T exchanges associated with - N collisions. Finally, it is shown that the reaction does not constitute an effective depopulating mechanism of N atoms as most of the N atoms so created are reconverted to the N by collisions on the wall and quenching.
TL;DR: In contrast to traditional theories, PNP computes the electric field in the open channel from all of the charges in the system, by a rapid and accurate numerical procedure, and is a theory of the shielding of fixed charge of the channel by mobile charge and by the ionic atmosphere in and near the channel's pore.
TL;DR: In this paper, a physically-based, semi-empirical, local model for transverse-field dependent electron and hole mobility in MOS transistors is presented to accurately predict the measured relationship between the effective mobility and effective electric field over a wide range of substrate doping and bias.
Abstract: A new, comprehensive, physically-based, semiempirical, local model for transverse-field dependent electron and hole mobility in MOS transistors is presented. In order to accurately predict the measured relationship between the effective mobility and effective electric field over a wide range of substrate doping and bias, we account for the dependence of surface roughness limited mobility on the inversion charge density, in addition to including the effect of coulomb screening of impurities by charge carriers in the bulk mobility term. The result is a single mobility model applicable throughout a generalized device structure that gives good agreement with measured mobility data and measured MOS I-V characteristics over a wide range of substrate doping, channel length, transverse electric field, substrate bias, and temperature.
TL;DR: In this article, the authors derived exact expressions for remote electric and magnetic fields as a function of the time and height-varying charge density on the lightning channel for both leader and return-stroke processes.
Abstract: We derive exact expressions for remote electric and magnetic fields as a function of the time- and height-varying charge density on the lightning channel for both leader and return-stroke processes. Further, we determine the charge density distributions for six return-stroke models. The charge density during the return-stroke process is expressed as the sum of two components, one component being associated with the return-stroke charge transferred through a given channel section and the other component with the charge deposited by the return stroke on this channel section. After the return-stroke process has been completed, the total charge density on the channel is equal to the deposited charge density component. The charge density distribution along the channel corresponding to the original transmission line (TL) model has only a transferred charge density component so that the charge density is everywhere zero after the wave has traversed the channel. For the Bruce-Golde (BG) model there is no transferred, only a deposited, charge density component. The total charge density distribution for the version of the modified transmission line model that is characterized by an exponential current decay with height (MTLE) is unrealistically skewed toward the bottom of the channel, as evidenced by field calculations using this distribution that yield (1) a large electric field ramp at ranges of the order of some tens of meters not observed in the measured electric fields from triggered-lightning return strokes and (2) a ratio of leader-to-return-stroke electric field at far distances that is about 3 times larger than typically observed. The BG model, the traveling current source (TCS) model, the version of the modified transmission line model that is characterized by a linear current decay with height (MTLL), and the Diendorfer-Uman (DU) model appear to be consistent with the available experimental data on very close electric fields from triggered-lightning return strokes and predict a distant leader-to-return-stroke electric field ratio not far from unity, in keeping with the observations. In the TCS and DU models the distribution of total charge density along the channel during the return-stroke process is influenced by the inherent assumption that the current reflection coefficient at ground is equal to zero, the latter condition being invalid for the case of a lightning strike to a well-grounded object where an appreciable reflection is expected from ground.
TL;DR: In this article, the Vickers indentation technique was used to detect cracks in a piezoelectric lead-zirconium-titanate (PZT) material under simultaneous mechanical loading and applied electric fields.
Abstract: Crack propagation in a piezoelectric lead–zirconium–titanate (PZT) material under simultaneous mechanical loading and applied electric fields is studied using the Vickers indentation technique. It is demonstrated experimentally that electric fields can inhibit or enhance crack propagation in piezoelectric materials. Cracks introduced by indentation are observed to propagate less under a positive applied electric field (the polarity of the field was the same as that for poling), whereas under a negative applied electric field, crack propagation is enhanced. Such an effect is observed to be more profound with increasing electric-field strength and decreasing mechanical loading. Attempts are made to compare these experimental observations with the results of various theoretical analyses. A mechanism for the change in crack propagation behavior of the piezoelectric PZT material under applied electric fields is presented.
TL;DR: In this paper, the authors investigated the nonlinear development of collisionless driven reconnection and the consequent energy conversion process between the field and particles in a sheared magnetic field by means of a two-and-one-half-dimensional particle simulation.
Abstract: Nonlinear development of collisionless driven reconnection and the consequent energy conversion process between the field and particles in a sheared magnetic field are investigated by means of a two-and-one-half-dimensional particle simulation. Magnetic reconnection takes place in two steps irrespective of a longitudinal magnetic field, but the growth rate of the reconnection field varies in proportion to the E×B drift velocity at an input boundary. It is clearly observed that the triggering mechanism of collisionless driven reconnection for the fast growing phase changes from an electron meandering dominance in a weak longitudinal field to an electron inertia dominance in a strong field. The electron acceleration and heating take place in the reconnection area under the influence of reconnection electric field, while the electron energy is converted to the ion energy through the action of an electrostatic (ambipolar) field excited by magnetic compression in the downstream. It is also found that, in the presence of a longitudinal magnetic field, the electron acceleration by the reconnection field takes place effectively and the generated force-free current is maintained for a long period while forming an asymmetric spatial profile of current layer.
TL;DR: In this paper, a theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday.
Abstract: A theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday. Results are obtained, in concentric sphere geometry, for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions, negative ions and metastable oxygen molecules, coupled with Poisson's equation. A series of `saw-toothed' current pulses of period about is predicted with a DC current level. Accompanying the current peaks are discrete pulses of light 30 ns wide. Successive `shells' of positive ions, from successive current pulses, carry 96% of the mean current. The mean current - voltage relationship has the classic square-law form. The seed electrons required for successive pulses are detached from negative ions by metastable oxygen molecules. Photo-ionization is crucial for the discharge at the anode and for the formation of negative ions throughout the gap. The pulse frequency varies with applied voltage and is found to be approximately proportional to the positive-ion mobility. The surface electric field at the central electrode remains close to Peek's onset field. The origin of onset streamers is explained and sub-microsecond voltage pulses are found to produce streamers. The results for concentric-cylinder electrodes are described briefly.
TL;DR: In this article, the electric field induced phase transition behavior of lead lanthanum zirconate titanate stannate (PLZTS) ceramics was investigated.
Abstract: The electric field induced phase transition behavior of lead lanthanum zirconate titanate stannate (PLZTS) ceramics was investigated. PLZTS undergoes a tetragonal antiferroelectric (AFETet) to rhombohedral ferroelectric (FERh) phase transition with the application of an electric field. The volume increase associated with this antiferroelectric (AFE)–ferroelectric (FE) phase transition plays an important role with respect to actuator applications. This volume increase involves an increase in both transverse and longitudinal strains. The E field at which the transverse strain increases is accompanied by an abrupt jump in polarization. The longitudinal strain, however, lags behind this polarization jump exhibiting a slight decrease at the onset of phase switching. This decoupling was related to the preferentially oriented AFE domain configuration, with its tetragonal c-axis perpendicular to the applied electric field. It is suggested that phase switching involves multiple steps involving both structural tran...