Showing papers on "Electric potential published in 2003"

Pumping of liquids with ac voltages applied to asymmetric pairs of microelectrodes.

Abstract: The net flow of electrolyte induced by an ac electric potential applied to an array of asymmetric pairs of microelectrodes has recently been reported. The interaction between the oscillating electric field and the oscillating induced charge at the diffuse double layer on the electrodes results in a steady electro-osmotic velocity distribution on top of the electrodes. This slip velocity distribution is anisotropic and produces a net flow of fluid. This paper presents a theoretical analysis of the pumping phenomena based upon an electro-osmotic model in ac fields. The electrical equations are solved numerically using the charge simulation method. The bulk flow generated by the electro-osmotic slip velocity is calculated. The dependence of the fluid flow on voltage and frequency is described and compared to experiments.

Electrically charged compact stars and formation of charged black holes

Abstract: We study the effect of electric charge in compact stars assuming that the charge distribution is proportional to the mass density. The pressure and the density of the matter inside the stars are large, and the gravitational field is intense. This indicates that electric charge and a strong electric field can also be present. The relativistic hydrostatic equilibrium equation, i.e., the Tolman-Oppenheimer-Volkoff equation, is modified in order to include electric charge. We perform a detailed numerical study of the effect of electric charge using a polytropic equation of state. We conclude that in order to see any appreciable effect on the phenomenology of the compact stars, the electric fields have to be huge $(\ensuremath{\sim}{10}^{21}$ V/m), which implies that the total charge is $Q\ensuremath{\sim}{10}^{20}$ Coulomb. From the local effect of the forces experienced on a single charged particle, it is expected that each individual charged particle is quickly ejected from the star. This in turn produces a huge force imbalance, and the gravitational force overwhelms the repulsive Coulomb and fluid pressure forces. The star can then collapse to form a charged black hole before all the charge leaves the system.

Effects of charge and electrostatic potential on lightning propagation

Abstract: [1] Three-dimensional lightning mapping observations are compared to cloud charge structures and electric potential profiles inferred from balloon soundings of electric field in New Mexico mountain thunderstorms. For six individual intracloud and cloud-to-ground flashes and for a sequence of 36 flashes in one storm, the comparisons consistently show good agreement between the altitudes of horizontal lightning channels and the altitudes of electric potential extrema or wells. Lightning flashes appear to deposit charge of opposite polarity in relatively localized volumes within the preexisting lower positive, midlevel negative, and upper positive charge regions associated with the potential wells. The net effect of recurring lightning charge deposition at the approximate levels of potential extrema is to increase the complexity in the observed storm charge structure. The midlevel breakdown of both normal intracloud flashes and negative cloud-to-ground flashes is observed to be segregated by flash type into the upper and lower parts of the deep potential well associated with the midlevel negative charge. The segregation is consistent with perturbations observed in the bottom of the negative potential well due to embedded positive charge that was probably deposited by earlier flashes. It is also consistent with an expected tendency for vertical breakdown to begin branching horizontally before reaching the local potential minimum. The joint observations reconcile the apparent dichotomy between the complex charge structures often inferred from balloon soundings through storms and the simpler structures often inferred from lightning measurements.

Influence of Fixed Charge Density Magnitude and Distribution on the Intervertebral Disc: Applications of a Poroelastic and Chemical Electric (PEACE) Model

Abstract: A 3-dimensional formulation for a poroelastic and chemical electric (PEACE) model is presented and applied to an intervertebral disc slice in a 1-dimensional validation problem and a 2-dimensional plane stress problem. The model was used to investigate the influence of fixed charge density magnitude and distribution on this slice of disc material. Results indicated that the mechanical, chemical, and electrical behaviors were all strongly influenced by the amount as well as the distribution of fixed charges in the matrix. Without any other changes in material properties, alterations in the fixed charge density (proteoglycan content) from a healthy to a degenerated distribution will cause an increase in solid matrix stresses and can affect whether the tissue imbibes or exudes fluid under different loading conditions. Disc tissue with a degenerated fixed charge density distribution exhibited greater solid matrix stresses and decreased streaming potential, all of which have implications for disc nutrition, disc biomechanics, and tissue remodeling. It was also seen that application of an electrical potential across the disc can induce fluid transport.

FAST observations of ion solitary waves

Abstract: [1] Measurements from the FAST spacecraft are used to show that ion solitary waves observed at the lower edge of the acceleration region travel at velocities faster than the associated auroral proton beams. The parallel phase velocity is consistent with the acoustic speed in the reference frame of the proton beam, strongly suggesting these waves are an ion acoustic mode. Their high phase velocity places them outside the ion beam population and rules out the ion two-stream instability as their source. These low-altitude structures may arise out of turbulence generated at the lower edge of the acceleration region. Their preferential observation at FAST altitudes may result from their high velocity combined with weak Landau damping that is restricted to the tenuous hot plasma sheet ions near the loss cone. Three different methods for estimating the velocity of these structures are examined. For the FAST antennae configuration it is found that signal delays between Langmuir probes operated in either current mode or voltage mode cannot provide valid estimates of the velocities. Instead, velocities are estimated by measuring the energy shift in the electron distribution within the negative potential well of the solitary wave. Using the measured wave potential and electric field, the scale size and velocity of the structures are calculated. Asymmetric solitary waves, sometime described as weak double layers, are also examined and shown to have no significant net potential. These new velocity estimates contrast sharply with reports based upon Viking observations and differ by about a factor of 2 from recent estimates deduced from Polar observations. These results are discussed in the context of previous estimates along with possible sources of error.

Analytical model of a dual frequency capacitive sheath

Abstract: In recent years, there has been an increased interest in capacitively coupled plasma discharges which are operated with two frequencies. An analytical sheath model for a capacitively coupled radio-frequency plasma discharge operated with two frequencies is proposed and studied under the assumptions of a time-independent, collisionless ion motion. Expressions are obtained for the time-average electric potential within the sheath, nonlinear motion of the electron sheath boundary and nonlinear instantaneous sheath voltage. The derived model is valid under the condition that the low frequency (lf) electric field Elf in the sheath is much higher than the high frequency (hf) electric field Ehf. This condition is fulfilled within typical dual frequency conditions. It is shown, however, that the hf electric field modifies the sheath structure significantly because of the electron response to Ehf. This model has been compared to particle-in-cell plasma simulations, finding good quantitative agreement. We present the dependence of the maximum sheath width and the dc sheath voltage drop on the hf/lf current ratio and on the hf/lf frequency ratio.

Interfacial cracks between piezoelectric and elastic materials under in-plane electric loading

Abstract: A new experimental technique for accelerated fatigue crack growth tests was recently developed (Du et al., 2001). The technique, which uses piezoelectric actuators, enables application of cyclic loading at frequencies several orders higher than that by mechanical loading. However, the validity of this technique relies on the equivalence between piezoelectric and mechanical loading. In this paper, the behavior of an interfacial crack between a piezoelectric material and an elastic material under in-plane electric loading is studied. The displacement mismatch along a bonded interface due to electric potential loading on the piezoelectric material is modeled by inserting an array of uniformly distributed dislocations along the interface. By means of Fourier transformation methods, the governing equations are converted to an integral equation, which is then converted to a standard Hilbert problem. A closed form solution for stresses, electric field, and electric displacements along the bonded interface is obtained. The results agree very well with those obtained from numerical simulations. The results show that the closed form solution is accurate not only for far field distributions of stresses and electric variables, but also for the asymptotic distributions near the crack tip. The solution also suggests the likelihood of domain switching in the piezoelectric material near the crack tip, a process that may influence the interfacial fracture resistance.

Protein Adsorption Kinetics under an Applied Electric Field: An Optical Waveguide Lightmode Spectroscopy Study

Abstract: The controlled surface placement of protein molecules represents a crucial step toward many new biotechnological devices and processes A promising means of directing the structure and formation rate of an adsorbed protein layer is through an applied electric potential difference We present here a method for continuously measuring the protein adsorption under a direct current voltage using optical waveguide lightmode spectroscopy An indium tin oxide-coated waveguiding sensor chip serves as the anode and adsorbing substrate, and a platinum counter electrode serves as the cathode in a parallel plate arrangement For (negatively charged) human serum albumin in either pure water or N-[2-hydroxyethyl]piperazine-N‘-ethanesulfonic acid (HEPES) buffer, we find the transport-limited and initial surface-limited rates of adsorption to significantly increase with the applied potential For (positively charged) horse heart cytochrome c, we observe no influence of the voltage on the transport-limited adsorption rate

Double Layer of a Gold Electrode Probed by AFM Force Measurements.

Abstract: Colloidal probe atomic force microscopy was used to determine the electric double layer interactions between a gold electrode and a spherical silica probe. The double layer properties of the gold/solution interface were varied through the pH and salt concentration of the electrolyte, as well as by externally applying an electric potential. The double layer potentials ψd of the gold surface were obtained by fitting the force−distance curves according to the DLVO (Derjaguin−Landau−Verwey−Overbeek) theory, using earlier obtained values for the double layer potential of the silica probe as input parameter. It was found that the gold electrode combines the features of reversible and polarizable interfaces; i.e., its charge and potential are determined by both the solution pH and the external potential. The pH dependence is attributed to proton adsorption and desorption from oxidic groups on the gold surface. In the potential range studied, ψd varies linearly with the applied potential; the variation in ψd is r...

High-latitude ionospheric electric field variability and electric potential derived from DE-2 plasma drift measurements: Dependence on IMF and dipole tilt

Abstract: [1] In this study the characteristics of electric field variability are investigated by using the sample standard deviations estimated from plasma drift measurements obtained during the Dynamics Explorer 2 (DE-2) mission. The spatial distribution of the standard deviation over the area poleward of 45° magnetic latitude and its climatological behavior with respect to the magnitude and orientation of the interplanetary magnetic field (IMF) and the dipole tilt angle (season) are examined. In comparison with past studies based on ground-based measurements and with results from a data assimilation model, this study quantifies the electric field variability with more complete spatial coverage and with more extensive climatological information and therefore is of importance to the problem of the global Joule heating estimation in thermospheric general circulation modeling. In general, the magnitude of the standard deviation exceeds the strength of the mean electric field in most of the polar area, especially under northward IMF conditions. In contrast to the climatological electric field, whose magnitude tends to be most intense in the polar cap, the standard deviation generally intensifies in the vicinity of the convection reversal and the cusp. Under most IMF clock angles the area of the largest electric field variability lies near the cusp; under the southward BZ condition the area extends toward the potential maximum on the dawn side and toward the region of strong sunward convection in the afternoon, while under the positive BY condition the area extends poleward of the potential maximum on the dawn side. The analysis reveals that electric field variability varies with magnetic latitude, magnetic local time, IMF, and season in a manner distinct from that of the climatological electric field. This indicates that empirical models and data assimilation models designed to reproduce the average electric potential or the average electric fields correctly are not necessarily well-suited to represent the squared electric fields or the electric field variability correctly.

Io‐related Jovian auroral arcs: Modeling parallel electric fields

Abstract: [1] Recent observations of auroral arcs on Jupiter suggest that electrons are being accelerated downstream from Io's magnetic footprint, creating detectable emissions. The downstream electron acceleration is investigated using one-dimensional spatial, two-dimensional velocity static Vlasov solutions under the constraint of quasi-neutrality and an applied potential drop. The code determines self-consistent charged particle distributions and potential structure along a magnetic field flux tube in the upward (with respect to Jupiter) current region of Io's wake. The boundaries of the flux tube are the Io torus on one end and Jupiter's ionosphere on the other. The results indicate that localized electric potential drops tend to form at 1.5-2.5 Rj Jovicentric distance. A sufficiently high secondary electron density causes an auroral cavity to be produced similar to that on Earth. Interestingly, the model results suggest that the proton and the hot electron population in the Io torus control the electron current densities between the Io torus and Jupiter and thus may control the energy flux and the brightness of the aurora downstream from Io's magnetic footprint. The parallel electric fields also are expected to create an unstable horseshoe electron distribution inside the auroral cavity, which may lead to the shell electron cyclotron maser instability. Results from our model suggest that in spite of the differing boundary conditions and the large centrifugal potentials at Jupiter, the auroral cavity formation may be similar to that of the Earth and that parallel electric fields may be the source mechanism of Io-controlled decametric radio emissions.

Charge expulsion and electric field in superconductors

Abstract: The theory of hole superconductivity predicts that when a metal goes superconducting negative charge is expelled from its interior towards the surface. As a consequence the superconductor in its ground state is predicted to have a nonhomogeneous charge distribution and an outward pointing electric field in its interior. Here we propose equations to describe the behavior of the charge density and electric field in superconductors, and solve them for a spherical geometry. The magnitude of the predicted interior electric field depends on superconducting parameters such as the condensation energy and the London penetration depth and is found to be of order ${10}^{6}\mathrm{V}/\mathrm{c}\mathrm{m}.$ A physical interpretation of the result is given. It is predicted that for small superconducting bodies (compared to the penetration depth) an electric field outside the superconductor should result from this physics. This may explain a recent experimental observation in Nb metal clusters.

Complex formation in solutions of oppositely charged polyelectrolytes at different polyion compositions and salt content

Abstract: The formation of complexes in solutions containing positively charged polyions (polycations) and a variable amount of negatively charged polyions (polyanions) has been investigated by Monte Carlo simulations. The polyions were described as flexible chains of charged hard spheres interacting through a screened Coulomb potential. The systems were analyzed in terms of cluster compositions, structure factors, and radial distribution functions. At 50% charge equivalence or less, complexes involving two polycations nd one polyanion were frequent, while closer to charge equivalence, larger clusters were formed. Small and neutral complexes dominated the solution at charge equivalence in a monodisperse system, while larger clusters again dominated the solution when the polyions were made polydisperse. The cluster composition and solution structure were also examined as functions of added salt by varying the electrostatic screening length. The observed formation of clusters could be rationalized by a few simple rules. (Less)

Multi-field variational formulations and related finite elements for piezoelectric shells

Abstract: Smart structures technology characterized by structurally integrated sensors and actuators has recently expanded significantly especially as regards lightweight constructions in aeronautics and robotics, e.g. to allow vibration suppression and noise attenuation. In order to be capable of solving these complex issues the finite element method as a well established design tool has to be extended. This paper focuses on shallow sandwich composite shell structures with thin piezoelectric patches bonded to the surfaces. For the proper design of plate and shell structures with integrated piezoelectric materials, various variational formulations and corresponding finite elements are presented. The starting point is the well known two-field variational formulation where the linear piezoelectric effect is taken into account so that the displacements and the electric potential serve as independent variables. Here, the mostly assumed linear variation of the electric potential through the thickness is assumed. Next, it is shown that a quadratic variation of the electric potential through the thickness can be deduced directly from the charge conservation condition. This quadratic variation of the electric potential in the thickness direction is compared with the linear gradient of the first two-field variational formulation. Moreover, in order to allow the implementation of alternative formulations of the constitutive equations by switching of the independent variables and nonlinear material behaviour, a three-field variational formulation is presented in analogy to the Hu–Washizu principle. Adopting this variational principle a hybrid finite element is derived where the dielectric displacement is formulated as an additional degree of freedom. This independent variable can be condensed on the element level and does not enter the system of equations. For the first time all these different variational formulations are developed for a Reissner–Mindlin shallow shell element formulation and compared with each other.

Measurement of built-in electrical potential in III–V solar cells by scanning Kelvin probe microscopy

Abstract: We report on direct measurements of the built-in electrical potential in III–V semiconductor-based solar cell devices by using scanning Kelvin probe microscopy. Potential profiles on cross sections of the devices were measured quantitatively and spatially resolved in open and short circuits, under and without illuminations, with selective photon energies matching band gaps of the junctions. The measurements provide valuable information about the electrical properties of the devices, and are useful for understanding the performance of solar cells. On a GaInP2-single junction cell, two potential features were measured and were assigned to the p-n junction and the potential barrier at the interface between the GaInP2 base layer and the GaAs substrate. The potential on the p-n junction is photoactive, and that on the GaInP2/GaAs interface is photoinactive. On a GaInP2/GaAs tandem cell, two potential features were measured near the top and the bottom p-n junctions. When the sample was illuminated by light with...

The Electric Field

Abstract: 9. a) Find the electric field at the point A (8,0) due to the charges Q1 (0,-6) = 2 μC and Q2 (0,6) = 2 μC and where the coordinates are measured in meters. b) What is the total force exerted by Q1 and Q2 on a charge Q3 = 6 μC located at A. c) Find the electric potential at A (8,0) and B (0,0). d) How much work is required to carry a 6 μC from A (8,0) to O (0,0). Answer: a) = A E r 216 i r N/C. b) ..... c) VA = 3600 V; VO = 6000 V. d) WA→O = 0.144 J

Donor‐related density of states and polarizability in a GaAs‐(Ga, Al)As quantum‐well under hydrostatic pressure and applied electric field

Abstract: Theoretical calculations have been used to assess the influence of both an external electric field and hydrostatic stress on the binding energy, impurity polarizability, as a function of the impurity position and density of states for shallow-donor impurities in a GaAs–(Ga, Al)As quantum well. The binding energy maximum is shifted toward the wall at z = –L/2 of the quantum well for increasing values of electric field (keeping a constant pressure) and increasing values of pressure (keeping a constant electric field). The polarizability follows closely the behavior of the binding energy so for smaller binding energies the polarizability is large showing a more delocalized electron cloud. Also, it has been observed that the density of states depends strongly on the applied hydrostatic stress and electric field. In the absence of an electric field the energy level is degenerate for symmetrical positions of the impurities with respect to the center of the quantum well. However, this degeneracy is broken when an electric field is applied in the growth direction of the structure. Associated with this, the density of states becomes richer in structure

Modeling the effect of dust on the plasma parameters in a dusty argon discharge under microgravity.

Abstract: A dusty radio-frequency argon discharge is simulated with the use of a two-dimensional fluid model. In the model, discharge quantities, such as the fluxes, densities, and electric field are calculated self-consistently. The charge and density of the dust are calculated with an iterative method. During the transport of the dust, its charge is kept constant in time. The dust influences the electric potential distribution through its charge and the density of the plasma through recombination of positive ions and electrons on its surface. Results are presented for situations in which the dust significantly changes the discharge characteristics, both by a strong reduction of the electron density and by altering the electric potential by its charge. Simulations for dust particles having a radius of 7.5 microm show that a double space charge layer is created around the sharp boundary of the dust crystal. A central dust-free region (void) is created by the ion drag force. Inside this void a strong increase of the production of argon metastables is found. This phenomenon is in agreement with experimental observations, where an enhanced light emission is seen inside the void.

Quasi-steady drift paths in a model magnetosphere with AMIE electric field: Implications for ring current formation

Abstract: [1] Recent measurements show that magnetospheric convection electric fields during the main phases of magnetic storms are much more complicated in spatial structure than the electric fields that have generally been used to model formation of the stormtime ring current. To investigate the transport effects of such more realistic stormtime electric fields on magnetospheric charged particles, we map the Assimilative Model of Ionospheric Electrodynamics (AMIE) electric potential functions analytically with a simple magnetic field model at selected times of interest during several magnetic storms from 1997–1998 and during the extremely large storm of July 2000. We calculated corresponding contours of constant Hamiltonian (kinetic plus potential energy) for first invariant values that range from 0 to 30 MeV/G (representative of equatorially mirroring cold plasma, ring current, and radiation-belt ions and electrons). These equatorial contours would constitute drift paths if the electric field were truly constant in time. We thus calculated how far along such quasi-drift paths the corresponding particles would have drifted after specific amounts of time, and we compare these quasi-drift characteristics with those obtained from a simple semiempirical model of the convection electric field. We find considerable variability among stormtime equatorial quasi-drift paths, reflecting the known variability of AMIE equipotentials. Patterns of equatorial quasi-drift in the simplified electric field model are (by construction) symmetric about the dawn-dusk meridian. During the main phases of storms, the equatorial electric field derived from AMIE tends to be strongest in an MLT sector several hours wide on the night side. This concentration of AMIE equipotentials provides a channel for rapid transport (requiring ∼20–30 min) for ions with first invariant values representative of the ring current population from the nightside neutral line to low L values (∼3–4) near dusk, where the partial ring current forms. During the extremely large “Bastille Day” storm of 15 July 2000 (minimum Dst = −300 nT) the drift patterns derived from AMIE show penetration of ions to as low as L ∼ 2. This deep penetration of ring current ions could help to account for the very strong ring current that was observed during this storm. The quasi-steady state drift properties help us anticipate the implications of a more realistic electric field model for the particle drifts that lead to the formation of the stormtime ring current.

A hydrogen atom in a superstrong magnetic field and the Zeldovich effect

Abstract: We consider the problem of a hydrogen atom in a superstrong magnetic field, B≫ B a =2.35×109 G. The analytical formulas that describe the energy spectrum of this atom are derived for states with various quantum numbers n ρ and m. A comparison with available calculations shows their high accuracy for B≫B a . We note that the derived formulas point to a manifestation of the Zeldovich effect, i.e., a rearrangement of the atomic spectrum under the influence of strong short-range Coulomb potential distortion. We discuss the relativistic corrections to level energies, which increase in importance with magnetic field and become significant for B≳1014 G. We suggest the parameters in terms of which the Zeldovich effect has the simplest form. Analysis of our precision numerical calculations of the energy spectrum for a hydrogen atom in a constant magnetic field indicates that the Zeldovich effect is observed in the spectrum of atomic levels for superstrong fields, B≳5×1011 G. Magnetic fields of such strength exist in neutron stars and, possibly, in magnetic white dwarfs. We set lower limits for the fields B min required for the manifestation of this effect. We discuss some of the properties of atomic states in a superstrong magnetic field, including their mean radii and quadrupole moments. We calculated the probabilities of electric dipole transitions between odd atomic levels and a deep ground level.

Semiconductor memory device

Abstract: A semiconductor memory device of this invention enables high rate readout of stored data without read failure. The semiconductor memory device has a group of memory transistors including a plurality of memory transistors connected in series and a data readout line, through which data stored in the memory transistors is outputted. A sense amplifier is connected to the data readout line. The data readout line is pre-charged to a first electric potential by a transistor for pre-charge. A first transistor for keeping voltage controlled by the sense amplifier is connected to the data readout line, and a second transistor for keeping voltage is connected between the first transistor for keeping voltage and a node at the first electric potential. Furthermore, the semiconductor memory device of this invention has a delay circuit generating a delay signal to turn on the second transistor for keeping voltage, after pre-charging by the transistor for pre-charge is completed.

Electro-optic effect in a semi-parabolic quantum well with an applied electric field

Abstract: By using the compact density matrix approach, the electro-optic effect (EOE) in a semi-parabolic quantum well (QW) with an applied electric field has been theoretically investigated. Via a variant of displacement harmonic oscillation, the exact electronic states in the semi-parabolic QW with an applied electric field are obtained. Numerical results on typical GaAs material reveal that the electro-optic effect nearly linearly increases with the increasing of magnitude of the electric field, but it monotonously decreases with the increasing of confining potential frequency of the semi-parabolic QW. The EOE in the model investigated is 102 times larger than that in the symmetric parabolic QW under the same electric field and the same frequency of parabolic confining potential, which is due to the self-asymmetry of the system and the electric field effect.