Showing papers on "Electric potential published in 2001"

An improved model of ionospheric electric potentials including substorm perturbations and application to the Geospace Environment Modeling November 24, 1996, event

Abstract: An improved model of ionospheric electric potentials/convection patterns is presented here. This model will produce potentials for any desired level of interplanetary magnetic field (IMF), solar wind velocity, number density, and dipole tilt angle, as well as an optional value for the AL index. The following improvements have been made: (1) Terms for solar wind electric field and dynamics pressure have been added. (2) Nonlinear changes in the potentials as the magnitude of the IMF increases, owing to the decreasing effective width of the solar wind coupling region, are now allowed. (3) The lower boundary of the potential patterns is now variable according to the conditions, rather than fixed at an arbitrary location, resulting in fewer coefficients in the spherical harmonic expansion and smoother patterns. (4) The influence of magnetospheric substorms, or nightside processes, on the potential patterns is now included as a perturbation using the AL index as an optional controlling parameter. The utility of the new substorm component is demonstrated with the event on November 24, 1996, which had been chosen for the “Geospace Environment Modeling (GEM) Substorm Challenge.” By an examination of the potential patterns over the International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer chain, it is shown that the IMF alone is not sufficient to predict the electric potential patterns when there are substorms present, demonstrating the influence of the substorm “unloading” component. This model can reproduce the very complex changes that occur in the potential patterns as the IMF orientation rotates in the GSM Y-Z plane, and it is useful for scientific studies as input for other models or validation of computer simulation results. There is also a practical application of predicting “space weather” in the magnetosphere, on the basis of upstream solar wind/IMF measurements. The later application will become more effective when accurate methods become available for predicting the AL indices.

Electrochemical methods and devices for use in the determination of hematocrit corrected analyte concentrations

Abstract: Methods and devices for determining the concentration of an analyte in a physiological sample are provided. In the subject methods, the physiological sample is introduced into an electrochemical cell having a working and reference electrode. A first electric potential is applied to the cell and the resultant cell current over a period of time is measured to determine a first time-current transient. A second electric potential of opposite polarity is then applied and a second a time-current transient is determined. The preliminary concentration of the analyte is then calculated from the first and/or second time-current transient. This preliminary analyte concentration less a background value is then multiplied by a hematocrit correction factor to obtain the analyte concentration in the sample, where the hematocrit correction factor is a function of the preliminary analyte concentration and the variable γ of the electrochemical cell. The subject methods and devices are suited for use in the determination of a wide variety of analytes in a wide variety of samples, and are particularly suited for the determination of analytes in whole blood or derivatives thereof, where an analyte of particular interest is glucose.

Derivation of Poisson and Nernst-Planck equations in a bath and channel from a molecular model

Abstract: Permeation of ions from one electrolytic solution to another, through a protein channel, is a biological process of considerable importance. Permeation occurs on a time scale of micro- to milliseconds, far longer than the femtosecond time scales of atomic motion. Direct simulations of atomic dynamics are not yet possible for such long-time scales; thus, averaging is unavoidable. The question is what and how to average. In this paper, we average a Langevin model of ionic motion in a bulk solution and protein channel. The main result is a coupled system of averaged Poisson and Nernst-Planck equations (CPNP) involving conditional and unconditional charge densities and conditional potentials. The resulting NP equations contain the averaged force on a single ion, which is the sum of two components. The first component is the gradient of a conditional electric potential that is the solution of Poisson's equation with conditional and permanent charge densities and boundary conditions of the applied voltage. The second component is the self-induced force on an ion due to surface charges induced only by that ion at dielectric interfaces. The ion induces surface polarization charge that exerts a significant force on the ion itself, not present in earlier PNP equations. The proposed CPNP system is not complete, however, because the electric potential satisfies Poisson's equation with conditional charge densities, conditioned on the location of an ion, while the NP equations contain unconditional densities. The conditional densities are closely related to the well-studied pair-correlation functions of equilibrium statistical mechanics. We examine a specific closure relation, which on the one hand replaces the conditional charge densities by the unconditional ones in the Poisson equation, and on the other hand replaces the self-induced force in the NP equation by an effective self-induced force. This effective self-induced force is nearly zero in the baths but is approximately equal to the self-induced force in and near the channel. The charge densities in the NP equations are interpreted as time averages over long times of the motion of a quasiparticle that diffuses with the same diffusion coefficient as that of a real ion, but is driven by the averaged force. In this way, continuum equations with averaged charge densities and mean-fields can be used to describe permeation through a protein channel.

Analysis of piezoelectric coupled circular plate

Abstract: This paper deals with the vibration analysis of a circular plate surface bonded by two piezoelectric layers, based on the Kirchhoff plate model. The form of the electric potential field in the piezoelectric layer is assumed such that the Maxwell static electricity equation is satisfied. The validation of the theoretical model is done by comparing the resonant frequencies of the piezoelectric coupled circular plate obtained by the theoretical model and those obtained by finite-element analysis. The mode shape of the electric potential obtained from free vibration analysis is generally shown to be non-uniform in the radial direction in contrast to what is commonly assumed. The piezoelectric layer is shown to have an effect on the frequencies of the host structure. The proposed model for the analysis of a coupled piezoelectric circular plate provides a means to obtain the distribution of electric potential in the piezoelectric layer. The model provides design reference for piezoelectric material application, such as an ultrasonic motor.

Maps of ionospheric field‐aligned currents as a function of the interplanetary magnetic field derived from Dynamics Explorer 2 data

Abstract: A new technique for mapping field-aligned currents (FAC) with satellite magnetometer data has been used with Dynamics Explorer 2 measurements to produce an empirical model which maps the currents above the high-latitude ionosphere as a function of the interplanetary magnetic field (IMF), solar wind velocity, solar wind density, and dipole tilt angle. This technique uses scalar magnetic Euler potentials, derived from integrating the measured magnetic deviations in much the same way as electric potentials are derived from integrating electric fields. This method works with any configuration of two-dimensional distribution of the field-aligned current, rather than assuming that the currents are in the form of infinite sheets or belts. The radial current density is found by a surface Laplacian operator on the scalar field. The maps of the FAC produced with this new technique are more quantitative and detailed than most of the preceding statistical diagrams, and they yield much insight into how the currents vary as the IMF clock angle changes, and how the field-aligned current maps overlap the associated electric potential patterns. An optional component of the model shows changes in the currents associated with substorms, using the AL index as the controlling parameter. The most notable aspect of the substorm patterns is an increased region 0 current, which in addition to the region 2 current closes the majority of the current on the dusk side of the auroral surge. The results do not seem to agree with the traditional paradigm of the substorm current wedge closing through the ionosphere from dawn to dusk.

Direct Observation of Localized Parallel Electric Fields in a Space Plasma

Abstract: We report direct measurements of parallel electric fields related to particle acceleration in a collisionless space plasma The electric field is that of a monotonic potential ramp localized to $\ensuremath{\sim}10\mathrm{debye}$ lengths along the magnetic field Electrons accelerated by the parallel electric field are accompanied by intense electrostatic waves and nonlinear structures interpreted as electron phase-space holes

Electro-optical device

Abstract: An object of the present invention is to realize a numerical aperture higher than that of a pixel having a conventional construction by using a pixel circuit having a novel construction in an electro-optical device. Therefore, it is utilized that the electric potential of a gate signal line in a row except for an i-th row is set to a constant electric potential in a period except for when a gate signal line ( 106 ) in the i-th row is selected. A gate signal line 111 in an (i−1)-th row is also used as an electric current supply line for an EL element ( 103 ) controlled by the gate signal line ( 106 ) in the i-th row. Thus, wiring number is reduced and high numerical aperture is realized.

Modeling of Photovoltage and Photocurrent in Dye-Sensitized Titanium Dioxide Solar Cells

Abstract: By means of two-dimensional simulation calculations, a detailed analysis of the nanocrystalline TiO2 dye-sensitized solar cell (DSC) has been performed. A simplified scheme of the nanoporous structure, which is treated as if the TiO2 film is a continuous medium, is used for modeling. On the basis of material parameters, the model permits the determination of steady-state charge-carrier distributions, the calculation of I−V curves under illumination, dark characteristics, and the spectral response of a DSC. The spatial resolution of the model allows for the answer to the question of the spatial distribution of both the electric and the electrochemical potential in the cell. Thus, a deeper insight into the operation mechanism of a DSC is obtained. Nonnegligible drift currents are found. It is shown quantitatively that the electric potential drops mainly at the TCO/TiO2 interface and not at a Helmholtz layer. The role of the dark interfacial electrical potential difference (built-in potential) for the functi...

Ground State Energy of the One-Component Charged Bose Gas

Abstract: The model considered here is the “jellium” model in which there is a uniform, fixed background with charge density − eρ in a large volume V and in which N = ρV particles of electric charge +e and mass m move — the whole system being neutral. In 1961 Foldy used Bogolubov’s 1947 method to investigate the ground state energy of this system for bosonic particles in the large ρ limit. He found that the energy per particle is −0.402r s −3/4 me 4/ħ2 in this limit, where r s = (3/4πρ)1/3 e 2 m/ħ2. Here we prove that this formula is correct, thereby validating, for the first time, at least one aspect of Bogolubov’s pairing theory of the Bose gas.

Theoretical/numerical study of electrohydrodynamic pumping through pure conduction phenomenon

Abstract: In an isothermal liquid, only the Coulomb force which is the force acting on the free charges, can contribute to the net electrohydrodynamic (EHD) motion. In the absence of a direct charge injection or induction, the charges can be generated through the dissociation process of the fluid. The generated charges by dissociation are redistributed by the applied electric field, resulting in the heterocharge layers around the electrodes. The pumping of an isothermal liquid without ion injection is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes. This type of pumping is referred to as the conduction pumping. This paper investigates the pressure head generated by the conduction pumping mechanism theoretically through the numerical solutions. For this purpose, a theoretical model for the static case (i.e., without a fluid motion) is established and a numerical code using finite volume method is developed. Electric potential, electric field, charge density, and electric body force distributions for the selected electrode configuration are presented. The generated pressure as a function of the applied voltage is also presented. The numerical results confirm the EHD conduction pumping concept theoretically.

Screening of a point charge by an anisotropic medium: Anamorphoses in the method of images

Abstract: We extend the classical dielectric image problem for an external point charge interacting with a semi-infinite medium to the case of an anisotropic dielectric. We show that the exterior potential is a solution to an unconventional image problem. By contrast the interior potential is not a solution to any simple image system; instead it can be obtained through an anamorphic transformation of an image solution. We calculate the volume bound charge density that is induced within the anisotropic dielectric and distinguishes it from an isotropic medium where the volume density vanishes. This solution provides a very simple and physically relevant example in which the physics of the surface and volume bound charge densities in a polarized dielectric can be analyzed.

On the correction of the Bernoulli-Euler beam theory for smart piezoelectric beams

Abstract: The present paper is devoted to the development of a simple Bernoulli-Euler type beam theory for smart piezoelectric composite beams. It is the scope of this paper to formulate a formally purely mechanical beam theory taking into account the coupling to the electric field by means of the direct piezoelectric effect. Different electric boundary conditions, electroded layers with either the electric potential or the total charge being prescribed, or non-electroded layers, are considered. Approximations for the electric field depending on the actually realized electric boundary conditions are then utilized in the present formulation. Finally a beam model is obtained taking into account the electromechanical coupling by means of effective stiffness parameters. Results obtained by using this simple model are compared to two-dimensional electromechanically coupled finite element calculations. A very good agreement for both the mechanical and the electrical response is found, showing that the accuracy of the present one-dimensional theory is comparable to that of the two-dimensional finite element calculations.

Love waves in piezoelectric coupled solid media

Abstract: The propagation of Love waves in a piezoelectric lamina bonded onto a semi-infinite solid medium is investigated in this paper. The dispersive characteristics and the mode shapes of the deflection and the electric potential in the thickness direction of the piezoelectric layer are theoretically derived. Numerical simulations show that the phase velocities initiate at the shear wave velocity of the host medium and tend towards the Bleustein-Gulyayev surface wave velocity for the piezoelectric layer at high wavenumbers for the first mode. The first two mode shapes of the electric potential correspond to a half-cosine and a full-cycle sinusoidal distribution, respectively, and become distorted as the wavenumber increases. These findings are significant in the application of inter-digital transducers for surface wave excitation in structural health monitoring.

The dynamical response of a hydrogel fiber to electrochemical stimulation

Abstract: The preparation of a smart hydrogel fiber based on chitosan/poly(ethylene glycol) is presented. The dynamics of this hydrogel fiber in response to electric stimulation is reported. The effects of a number of factors have been systematically studied, including the fiber diameter, concentration of the crosslinking agent, electric potential imposed across the fiber, pH, and ionic strength of the bath solution. Fiber deformation is expressed in terms of the curvature at the midlength of the fiber for various times. The number of bending to a given extent within a given time period is used to describe the rate of cyclic deformation. Our experimental results show a stable reversibility of bending behavior under the applied electric field. The bending curvature is proportional to the intensity of the applied electric potential. Although adequate mechanical properties are maintained, the rate of deformation can be improved via the adjustment of a number of the aforementioned extrinsic factors. These observations are interpreted in terms of fiber stiffness, fixed charge density, and swelling pressure, which depend on the hydrogel equilibrium states in different pH and ionic environments along with the electrochemical reactions under the electric field. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 236–246, 2001

On different approaches to calculating lightning electric fields

Abstract: Three different approaches to the computation of lightning electric fields are compared. These approaches are the traditional dipole (Lorentz condition) technique and two versions of the monopole (continuity equation) technique. The latter two techniques are based on two different formulations of the continuity equation, one used by Thottappillil et al. [1997] and the other by Thomson [1999], the difference between the formulations being related to different treatments of retardation effects. The three approaches involve the same expression for the vector potential but different expressions for the scalar potential. It is analytically shown that the three different expressions for the scalar potential are equivalent and satisfy the Lorentz condition. Further, the three approaches yield the same total fields and the same Poynting vectors. However, expressions in the three approaches for the individual electric field components in the time domain, traditionally identified by their distance dependence as electrostatic, induction, and radiation terms, are different, suggesting that explicit distance dependence is not an adequate identifier. It is shown that the so identified individual field components in the electric field equation in terms of charge density derived by Thottappillil et al. [1997] are equivalent to the corresponding field components in the traditional equation for electric field in terms of current based on the dipole technique. However, the individual field components in the electric field equation based on Thomson's [1999] approach are not equivalent to their counterparts in the traditional dipole technique equation. Further, in Thottappillil et al.'s [1997] technique and in the traditional dipole technique, the gradient of scalar potential contributes to all three electric field components, while in Thomson's [1999] technique it contributes only to the electrostatic and induction components. Calculations of electric fields at different distances from the lightning channel show that the differences between the corresponding field components identified by their distance dependence in different techniques are considerable at close ranges but become negligible at far ranges.

Calculating the influence of external changes on the photoluminescence of a CdS quantum dot

Abstract: The influence of external charges on the radiative recombination rate of an electron−hole pair in a CdSe quantum dot is investigated via atomistic empirical pseudopotential calculations. It is found that, when a negative external charge is near the surface of a CdSe quantum dot, its Coulomb potential could be strong enough to pull the hole away from the electron and results in a reduction of the radiative recombination rate by a factor of 70. Distance, direction, charge number, and charge type dependences of this effect are investigated.

Method and apparatus for simulating physical fields

Abstract: In order to design on-chip interconnect structures in a flexible way, a CAD approach is advocated in three dimensions, describing high frequency effects such as current redistribution due to the skin-effect or eddy currents and the occurrence of slow-wave modes. The electromagnetic environment is described by a scalar electric potential and a magnetic vector potential. These potentials are not uniquely defined, and in order to obtain a consistent discretization scheme, a gauge-transformation field is introduced. The displacement current is taken into account to describe current redistribution and a small-signal analysis solution scheme is proposed based upon existing techniques for static fields in semiconductors. In addition methods and apparatus for refining the mesh used for numerical analysis is described.

Control of the electric-field profile in the Hall thruster

Abstract: Control of the electric-field profile in the Hall thruster through the positioning of an additional electrode along the channel is shown theoretically to enhance the efficiency. The reduction of the potential drop near the anode by use of the additional electrode increases the plasma density there, through the increase of the electron and ion transit times, causing the ionization in the vicinity of the anode to increase. The resulting separation of the ionization and acceleration regions increases the propellant and energy utilizations. An abrupt sonic transition is forced to occur at the axial location of the additional electrode, accompanied by the generation of a large (theoretically infinite) electric field. This ability to generate a large electric field at a specific location along the channel, in addition to the ability to specify the electric potential there, allows us further control of the electric-field profile in the thruster. In particular, when the electron temperature is high, a large abrupt voltage drop is induced at the vicinity of the additional electrode, a voltage drop that can comprise a significant part of the applied voltage.

Volume conductor effects on the spatial resolution of magnetic fields and electric potentials from gastrointestinal electrical activity.

Abstract: An analysis of the relative capabilities of methods for magnetic and electric detection of gastrointestinal electrical activity is presented. The model employed is the first volume conductor model for magnetic fields from GEA to appear in the literature. A mathematical model is introduced for the electric potential and magnetic field from intestinal electrical activity in terms of the spatial filters that relate the bioelectric sources with the external magnetic fields and potentials. The forward spatial filters are low-pass functions of spatial frequency, so more superficial external fields and potentials contain less spatial information than fields and potentials near the source. Inverse spatial filters, which are reciprocals of the forward filters, are high-pass functions and must be regularised by windowing. Because of the conductivity discontinuities introduced by low-conductivity fat layers in the abdomen, the electric potentials recorded outside these layers required more regularisation than the magnetic fields, and thus, the spatial resolution of the magnetic fields from intestinal electrical activity is higher than the spatial resolution of the external potentials. In this study, two smooth muscle sources separated by 5cm were adequately resolved magnetically, but not resolved electrically. Thus, sources are more accurately localized and imaged using magnetic measurements than using measurements of electric potential.

Field-effect flow control in a polydimethylsiloxane-based microfluidic system.

Abstract: The application of the field-effect for direct control of electroosmosis in a polydimethylsiloxane (PDMS)-based microfluidic system, constructed on a silicon wafer with a 2.0 microm electrically insulating layer of silicon dioxide, is demonstrated. This microfluidic system consists of a 2.0 cm open microchannel fabricated on a PDMS slab, which can reversibly adhere to the silicon wafer to form a hybrid microfluidic device. Aside from mechanically serving as a robust bottom substrate to seal the channel and support the microfluidic system, the silicon wafer is exploited to achieve field-effect flow control by grounding the semiconductive silicon medium. When an electric field is applied through the channel, a radial electric potential gradient is created across the silicon dioxide layer that allows for direct control of the zeta potential and the resulting electroosmotic flow (EOF). By configuring this microfluidic system with two power supplies at both ends of the microchannel, the applied electric potentials can be varied for manipulating the polarity and the magnitude of the radial electric potential gradient across the silicon dioxide layer. At the same time, the longitudinal potential gradient through the microchannel, which is used to induce EOF, is held constant. The results of EOF control in this hybrid microfluidic system are presented for phosphate buffer at pH 3 and pH 5. It is also demonstrated that EOF control can be performed at higher solution pH of 6 and 7.4 by modifying the silicon wafer surface with cetyltrimethylammonium bromide (CTAB) prior to assembly of the hybrid microfluidic system. Results of EOF control from this study are compared with those reported in the literature involving the use of other microfluidic devices under comparable solution conditions.

Ion fluxes considered in terms of membrane-surface electrical potentials

Abstract: Ions transported through plasma membranes encounter electrical charges, and associated electrical potentials, at the membrane surfaces. The ionic composition of the tissue-bathing medium influences both the surface charge density and the surface electrical potential. Changes in surface electrical potential may affect ion transport by altering two components of the chemical potential difference (Δµj ) of an ion through the membrane. First, the surface activity of the transported ion will change because of electrostatic attraction or repulsion. Second, the surface-to-surface transmembrane potential difference will change. (This is different from the bulk-phase-to-bulk-phase transmembrane potential difference measured with microelectrodes.) These changes in the components of the chemical potential may change the flux of an ion through the membrane even if the surface-to-surface Δµj (equal to the bulk-phase-to-bulk-phase Δµj ) remains constant. The Goldman-Hodgkin-Katz (GHK) flux equation does not take into account these surface-potential effects. The equation has been modified to incorporate surface potentials computed by a Gouy-Chapman-Stern model and surface ion activities computed by Nernst equations. The modified equation (despite several additional deficiencies of the GHK model) successfully predicts many transport phenomena not predicted by the standard GHK equation. Thus electrostatic effects may account for saturation, cis- and trans-inhibition, rectification, voltage gating, shifts in voltage optima, and other phenomena also attributable to other mechanisms.

Strategy for electromagnetic interconnect modeling

Abstract: In order to design on-chip interconnect structures in a flexible way, a computer-aided design approach is advocated in three dimensions, describing high-frequency effects such as current redistribution due to the skin effect or eddy currents and the occurrence of slow-wave modes. The electromagnetic environment is described by a scalar electric potential and a magnetic vector potential. These potentials are not uniquely defined and in order to obtain a consistent discretization scheme, a gauge transformation field is introduced. The displacement current is taken into account to describe current redistribution and a small-signal analysis solution scheme is proposed based upon existing techniques for fields in semiconductors.

Particle acceleration at an X‐type reconnection site with a parallel magnetic field

Abstract: The acceleration of charged particles at a two-dimensional magnetic reconnection site is investigated. The magnetic field has an X-type neutral point, while reconnection is driven by a uniform transverse electric field; the effect of including a uniform magnetic field component parallel to the driving electric field and transverse to the plane of the X point is studied. We focus on the adiabatic motion of strongly magnetized particles, a valid assumption everywhere for sufficiently strong parallel magnetic fields but one which excludes a region around the neutral point for weaker fields. The regime of interest is fast driven reconnection, in which the electric drift is strong. The trajectories of particles and their dependence on the magnitude of the parallel magnetic field component are investigated. Particles can be accelerated along the magnetic field lines both because of the coupling of the perpendicular electric drift with the parallel motion, which occurs in an inhomogeneous magnetic field, and the direct acceleration by the electric field. The energy spectra of particles leaving the reconnection site are also calculated.