Showing papers on "Electric potential published in 2010"

Lithium-Ion Battery State of Charge and Critical Surface Charge Estimation Using an Electrochemical Model-Based Extended Kalman Filter

Abstract: This paper presents a numerical calculation of the evolution of the spatially resolved solid concentration in the two electrodes of a lithium-ion cell. The microscopic solid concentration is driven by the macroscopic Butler–Volmer current density distribution, which is consequently driven by the applied current through the boundary conditions. The resulting, mostly causal, implementation of the algebraic differential equations that describe the battery electrochemical principles, even after assuming fixed electrolyte concentration, is of high order and complexity and is denoted as the full order model. The full order model is compared with the results in the works of Smith and Wang (2006, “Solid-State Diffusion Limitations on Pulse Operation of a Lithium-Ion Cell for Hybrid Electric Vehicles,” J. Power Sources, 161, pp. 628–639) and Wang et al. (2007 “Control oriented 1D Electrochemical Model of Lithium Ion Battery,” Energy Convers. Manage., 48, pp. 2565–2578) and creates our baseline model, which will be further simplified for charge estimation. We then propose a low order extended Kalman filter for the estimation of the average-electrode charge similarly to the single-particle charge estimation in the work of White and Santhanagopalan (2006, “Online Estimation of the State of Charge of a Lithium Ion Cell,” J. Power Sources, 161, pp. 1346–1355) with the following two substantial enhancements. First, we estimate the average-electrode, or single-particle, solid-electrolyte surface concentration, called critical surface charge in addition to the more traditional bulk concentration called state of charge. Moreover, we avoid the weakly observable conditions associated with estimating both electrode concentrations by recognizing that the measured cell voltage depends on the difference, and not the absolute value, of the two electrode open circuit voltages. The estimation results of the reduced, single, averaged electrode model are compared with the full order model simulation. DOI: 10.1115/1.4002475

In Situ Measurements of Stress-Potential Coupling in Lithiated Silicon

Abstract: An analysis of the dependence of electric potential on the state of stress of a lithiated-silicon electrode is presented. Based on the Larche and Cahn chemical potential for a solid solution, a thermodynamic argument is made for the existence of the stresspotential coupling in lithiated silicon; based on the known properties of the material, the magnitude of the coupling is estimated to be 60 mV/GPa in thin-film geometry. An experimental investigation is carried out on silicon thin-film electrodes in which the stress is measured in situ during electrochemical lithiation and delithiation. By progressively varying the stress through incremental delithiation, the relation between stress change and electric-potential change is measured to be 100–120 mV/GPa, which is of the same order of magnitude as the prediction of the analysis. The importance of the coupling is discussed in interpreting the hysteresis observed in the potential vs state-of-charge plots and the role of stress in modifying the maximum charge capacity of a silicon electrode under stress.

Direct Water Splitting Through Vibrating Piezoelectric Microfibers in Water

Abstract: We propose a mechanism, a piezoelectrochemical effect for the direct conversion of mechanical energy to chemical energy. This phenomenon is further applied for generating hydrogen and oxygen via direct water decomposition by means of as-synthesized piezoelectric ZnO microfibers and BaTiO3 microdendrites. Fibers and dendrites are vibrated with ultrasonic waves leading to a strain-induced electric charge development on their surface. With sufficient electric potential, strained piezoelectric fibers (and dendrites) in water triggered the redox reaction of water to produce hydrogen and oxygen gases. ZnO fibers under ultrasonic vibrations showed a stoichiometric ratio of H2/O2 (2:1) initial gas production from pure water. This study provides a simple and cost-effective technology for direct water splitting that may generate hydrogen fuels by scavenging energy wastes such as noise or stray vibrations from the environment. This new discovery may have potential implications in solving the challenging energy and e...

Pseudo-Two-Dimensional Model for Double-Gate Tunnel FETs Considering the Junctions Depletion Regions

Abstract: This paper presents a pseudo-2-D surface potential model for the double-gate tunnel field-effect transistor (DG-TFET). Analytical expressions are derived for the 2-D potential, electric field, and generation rate, and used to numerically extract the tunneling current. The model predicts the device characteristics for a large range of parameters and allows gaining insight on the device physics. The depletion regions induced inside the source and drain are included in the solution, and we show that these regions become critical when scaling the device length. The fringing field effect from the gates on these regions is also included. The validity of the model is tested for devices scaled to 10-nm length with SiO2 and high-? dielectrics by comparison to 2-D finite-element simulations.

Effects of Electroosmotic Flow on Ionic Current Rectification in Conical Nanopores

Abstract: The effects of electroosmotic flow (EOF) on the ionic current rectification (ICR) phenomenon in conical nanopores are studied comprehensively with use of a continuum model, composed of Nernst−Planck equations for the ionic concentrations, the Poisson equation for the electric potential, and Navier−Stokes equations for the flow field. It is found that the preferential current direction of a negatively charged nanopore is toward the base (tip) under a relatively high (low) κRt, the ratio of the tip radius size to the Debye length. The direction also changes with the charge polarity of the nanopore. The EOF effect on the ionic current rectification ratio in a conical nanopore becomes noticeable at an intermediate κRt and surface charge density of the nanopore, meanwhile increasing significantly with the applied voltage.

Semi-classical limit for Schrödinger equations with magnetic field and Hartree-type nonlinearities

Abstract: The semi-classical regime of standing wave solutions of a Schrodinger equation in the presence of non-constant electric and magnetic potentials is studied in the case of non-local nonlinearities of Hartree type. It is shown that there exists a family of solutions having multiple concentration regions which are located around the minimum points of the electric potential.

Broadband Spectral Change: Evidence for a Macroscale Correlate of Population Firing Rate?

Abstract: In [1972, Brindley and Craggs][1] measured the electric potential from the surface of the baboon brain using a 1-mm-diameter electrode. They found that the power in the 80–250 Hz frequency range of the electric potential time series was dynamically increased in motor areas during movement. Sites 2

Inverse spin-Hall effect in palladium at room temperature

Abstract: The inverse spin-Hall effect, conversion of a spin current into electromotive force, has been investigated in a simple Ni81Fe19/Pd film using the spin pumping. In the Ni81Fe19/Pd film, a spin current generated by the spin pumping is converted into an electromotive force using the inverse spin-Hall effect in the Pd layer. From the magnitude of the electromotive force, we estimated the spin-Hall angle for Pd as 0.01. This large spin-Hall angle for Pd is consistent with the prediction from the Gilbert damping enhancement due to the spin pumping. This value will be a crucial piece of information for spintronics device engineering.

Effect of surface stresses on the vibration and buckling of piezoelectric nanowires

Abstract: In this letter, we analyze the influence of surface stresses on the vibration and buckling behavior of piezoelectric nanowires by using the Euler-Bernoulli beam model. The effect of surface stresses is considered by applying a curvature-dependent distributed transverse loading along the beam. It is found that the resonant frequency of piezoelectric nanowires can be tuned by adjusting the applied electric potential, and its elastic constant and residual surface stress could be determined experimentally by measuring the critical electric potential at the occurrence of axial buckling. This study is helpful for design of nanowire-based devices and for characterization of the mechanical properties of nanowires.

Finite element analysis of Cymbal piezoelectric transducers for harvesting energy from asphalt pavement

Abstract: The purpose of this paper is to design a Cymbal for harvesting energy from asphalt pavement. Asphalt pavement is used popular on road. Part of the energies in the pavement caused by vehicle and gravity can be harvested by piezoelectric transducers. Cymbal is selected to harvest energy from asphalt pavement because of its low cost, high reliability and reasonable efficiency. The efficiency and coupling effects with pavement of Cymbals with various sizes are discussed through finite element analysis (FEA). The displacement difference at pavement surface between with and without Cymbal is developed to considering the coupling effects. The results show that the potential electric energy harvested from pavement increases with the diameter of Cymbal. However, the efficiency decreases with the increasing of Cymbal size. The diameter at 32 mm is suggested as the size of Cymbal. The potential electric energy increases near linearly with the diameter of end cap cavity base. Enough bonding area should be left to bond the end steel cap and PZT. There is a maximum electric energy existing when the top diameter of the end steel cap changes. The maximum electric energy is generated when the thickness of cap steel is about 0.3 mm. There is also a maximum electric energy existing when the height of end cap cavity changes. The Cymbals with thicker PZT can generate higher electric potential and storage electric energy. Considering the storage electric energy, cost, bonding between end steel cap and PZT and the pavement surface displacement, the Cymbal with 32 mm of total diameter, 22 mm of cavity base diameter, 10 mm of end cap top diameter, 0.3 mm of cap steel thickness, 2 mm of cavity height and 2 mm of PZT thickness is suggested as the optimum one for harvesting energy from asphalt pavement. The electric potential is about 97.33 V of the design Cymbal. 0.06 J electric energy can be storage in that Cymbal. Its potential maximum output power is about 1.2 mW at 20 Hz vehicle load frequency.

Conformations of end-tethered DNA molecules on gold surfaces: influences of applied electric potential, electrolyte screening, and temperature.

Abstract: We describe the behavior of 72mer oligonucleotides that are end-tethered to gold surfaces under the influence of applied electric fields The DNA extension is measured by fluorescence energy transfer as a function of the DNA hybridization state (single- and double-stranded), the concentration of monovalent salt in solution (100 μM to 1 M NaCl), the applied electrode potential (−06 to +01 V vs Pt), and the temperature (1 to 50 °C) At high ionic strength, the DNA conformations are very robust and independent of the applied electrode potential and temperature variations In solutions of medium ionic strength, the DNA conformation can be manipulated efficiently by applying bias potentials to the Au electrodes The molecules are repelled at negative potentials and attracted to the surface at positive potentials The conformation transition occurs abruptly when the electrode bias is swept by merely 01 V across the transition potential, which shifts negatively when the salinity is decreased The behavior can

Surface contact potential patches and Casimir force measurements

Abstract: We present calculations of contact potential surface patch effects that simplify previous treatments. It is shown that, because of the linearity of Laplace's equation, the presence of patch potentials does not affect an electrostatic calibration of a two-plate Casimir measurement apparatus. Using models that include long-range variations in the contact potential across the plate surfaces, a number of experimental observations can be reproduced and explained. For these models, numerical calculations show that if a voltage is applied between the plates which minimizes the force, a residual electrostatic force persists, and that the minimizing potential varies with distance. The residual force can be described by a fit to a simple two-parameter function involving the minimizing potential and its variation with distance. We show the origin of this residual force by use of a simple parallel capacitor model. Finally, the implications of a residual force that varies in a manner different from $1/d$ on the accuracy of previous Casimir measurements is discussed.

Nonlinear electric transport in graphene: Quantum quench dynamics and the Schwinger mechanism

Abstract: We present a unified view of electric transport in undoped graphene for finite electric field. The weak field results agree with the Kubo approach. For strong electric field, the current increases nonlinearly with the electric field as ${E}^{3/2}$. As the Dirac point is moved around in reciprocal space by the field, excited states are generated. This is analogous to the generation of defects in a finite-rate quench through a quantum-critical point, which we account for in the framework of the Kibble-Zurek mechanism. These results are also recast in terms of Schwinger's pair production and Landau-Zener tunneling. Other systems exhibiting a band structure with Dirac cones, in particular, cold atoms in optical lattices, should exhibit the same dynamics as well.

A phase field model of electromechanical fracture

Abstract: Structural reliability analyses of piezoelectric solids need the modeling of failure under coupled electromechanical actions. However, the numerical simulation of failure due to fracture based on sharp crack discontinuities may suffer in situations with complex crack topologies. This can be overcome by a diffusive crack modeling based on the introduction of a crack phase field. In this work, we develop a framework of diffusive fracture in piezoelectric solids. We start our investigation with the definition of a crack surface functional of the phase field that Γ -converges for vanishing length-scale parameter to a sharp crack topology. This functional provides the basis for the definition of suitable dissipation functions which govern the evolution of the crack phase field. Based on experimental results available in the literature, we suggest a non-associative dissipative framework where the fracture phase field is driven by the mechanical part of the coupled electromechanical driving force. This accounts for a hierarchical view that considers (i) the decrease of stiffness due to mechanical rupture as the primary action that is followed by (ii) the decrease of electric permittivity due to the generated free space. The proposed definition of mechanical and electrical parts of the fracture driving force follows in a natural format from a kinematic assumption, that decomposes the total strains and the total electric field into energy–enthalpy-producing parts and fracture parts, respectively. Such an approach allows the insertion of well-known anisotropic piezoelectric storage functions without change. We end up with a three-field-problem that couples the displacement with the electric potential and the fracture phase field. The latter is governed by a micro-balance equation, which appears in a very transparent form in terms of a history field containing a maximum fracture source obtained in the time history of the electromechanical process. This representation allows the construction of a very robust algorithmic treatment based on a operator split scheme, which successively updates in a typical time step the history field, the crack phase field and finally the two piezoelectric fields. The proposed model is considered to be the canonically simple scheme for the simulation of diffusive electromechanical crack propagation in solids. We demonstrate its modeling capacity by means of representative numerical examples.

High density conics in a magnetically expanding helicon plasma

Abstract: A two-dimensional mapping of ion density and plasma potential in a diverging magnetized low pressure (0.4 mTorr) carbon dioxide helicon plasma containing a double layer reveals the presence of high density conics (∼7×109 cm−3) along the most diverging magnetic field lines exiting the helicon source and connecting with the grounded expansion chamber. The density in the conic is about 30% greater than the density at the double layer and this results from local ionization associated with the presence of a high energy tail in the electron energy probability function. The plasma potential along the conic is constant at about 30 V.

Effect of Conductivity Variations within the Electric Double Layer on the Streaming Potential Estimation in Narrow Fluidic Confinements

Abstract: In this article, we investigate the implications of ionic conductivity variations within the electrical double layer (EDL) on the streaming potential estimation in pressure-driven fluidic transport through narrow confinements. Unlike the traditional considerations, we do not affix the ionic conductivities apriori by employing preset values of dimensionless parameters (such as the Dukhin number) to estimate the streaming potential. Rather, utilizing the Gouy-Chapman-Grahame model for estimating the electric potential and charge density distribution within the Stern layer, we first quantify the Stern layer electrical conductivity as a function of the zeta potential and other pertinent parameters quantifying the interaction of the ionic species with the charged surface. Next, by invoking the Boltzmann model for cationic and anionic distribution within the diffuse layer, we obtain the diffuse layer electrical conductivity. On the basis of these two different conductivities pertaining to the two different portions of the EDL as well as the bulk conductivity, we define two separate Dukhin numbers that turn out to be functions of the dimensionless zeta potential and the channel height to Debye length ratio. We derive analytical expressions for the streaming potential as a function of the fundamental governing parameters, considering the above. The results reveal interesting and significant deviations between the streaming potential predictions from the present considerations against the corresponding predictions from the classical considerations in which electrochemically consistent estimates of variable EDL conductivity are not traditionally accounted for. In particular, it is revealed that the variations of streaming potential with zeta potential are primarily determined by the competing effects of EDL electromigration and ionic advection. Over low and high zeta potential regimes, the Stern layer and diffuse layer conductivities predominantly dictate the streaming potential variations whereas ionic advection governs the streaming potential characteristics over intermediate zeta potential regimes. It is also inferred that traditional considerations may grossly overpredict the magnitude of streaming potential for narrow confinements in which significant conductivity gradients may prevail across the EDL.

High energy electron fluxes in dc-augmented capacitively coupled plasmas. II. Effects on twisting in high aspect ratio etching of dielectrics

Abstract: In high aspect ratio (HAR) plasma etching of holes and trenches in dielectrics, sporadic twisting is often observed. Twisting is the randomly occurring divergence of a hole or trench from the vertical. Many causes have been proposed for twisting, one of which is stochastic charging. As feature sizes shrink, the fluxes of plasma particles, and ions in particular, into the feature become statistical. Randomly deposited charge by ions on the inside of a feature may be sufficient to produce lateral electric fields which divert incoming ions and initiate nonvertical etching or twisting. This is particularly problematic when etching with fluorocarbon gas mixtures where deposition of polymer in the feature may trap charge. dc-augmented capacitively coupled plasmas (dc-CCPs) have been investigated as a remedy for twisting. In these devices, high energy electron (HEE) beams having narrow angular spreads can be generated. HEEs incident onto the wafer which penetrate into HAR features can neutralize the positive cha...

Origin of the Kink in Current-Density Versus Voltage Curves and Efficiency Enhancement of Polymer-C $_{\bf 60}$ Heterojunction Solar Cells

Abstract: Current-voltage (J-V ) curves of photovoltaic devices can reveal important microscopic phenomena when parameterization is properly related to physical processes. Here, we identify a pronounced effect of thermal annealing on the organic-cathode metal interface and show that this interface is related to the origin of the kink often observed in J-V curves close to the open circuit. We propose that isolated metal nanoclusters that form upon cathode evaporation lead to defect states close to the interface and change the electric field distribution in the device. We express this scenario with a modified equivalent circuit and consistently fit J- V curves as a function of the annealing process. The developed model is general in the sense that any physical process that leads to the change in electric potential as described in this paper will possibly lead to a kink in the J- V curves. Knowing the origin of the kink allowed us to largely increase the device efficiency of the archetypal material combination Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) -C. We fabricated solar cells with an efficiency of 1.85% under 100 mW/cm AM1.5 illumination by using a deliberately designed interpenetrating bilayer film morphology, aluminium as cathode and thermal annealing. This is so far the highest reported efficiency for this particular combination of materials.

Space charge effects in field emission: One dimensional theory

Abstract: The current associated with field emission is greatly dependent on the electric field at the emitting electrode. This field is a combination of the electric field in vacuum and the space charge created by the current. The latter becomes more important as the current density increases. Here, a study is performed using a modified classical one dimensional (1D) Child–Langmuir description that allows for exact solutions in order to characterize the contributions due to space charge. Methods to connect the 1D approach to an array of periodic three dimensional structures are considered.

Integrate and fire electronic neurons

Abstract: An integrate and fire electronic neuron is disclosed. Upon receiving an external spike signal, a digital membrane potential of the electronic neuron is updated based on the external spike signal. The electric potential of the membrane is decayed based on a leak rate. Upon the electric potential of the membrane exceeding a threshold, a spike signal is generated.

The Effects of the Span Configurations and Conductor Sag on the Electric-Field Distribution Under Overhead Transmission Lines

Abstract: The precise evaluation and mitigation of the electric field generated by overhead transmission lines has gained great interest due to its impact on health and environmental issues. This paper presents a more generalized technique to calculate the electric field generated by power transmission lines in three dimension coordinates. This technique has been evolved, formulated, and applied to an Egyptian 500-kV single-circuit transmission line to evaluate the effects of line topology and terrain topography on the computed electric field. The results are compared with those produced by a 2-D technique.

Static analysis of anisotropic functionally graded magneto-electro-elastic beams subjected to arbitrary loading

Abstract: This paper considers the analytical and semi-analytical solutions for anisotropic functionally graded magneto-electro-elastic beams subjected to an arbitrary load, which can be expanded in terms of sinusoidal series. For the generalized plane stress problem, the stress function, electric displacement function and magnetic induction function are assumed to consist of two parts, respectively. One is a product of a trigonometric function of the longitudinal coordinate (x) and an undetermined function of the thickness coordinate (z), and the other a linear polynomial of x with unknown coefficients depending on z. The governing equations satisfied by these z-dependent functions are derived. The analytical expressions of stresses, electric displacements, magnetic induction, axial force, bending moment, shear force, average electric displacement, average magnetic induction, displacements, electric potential and magnetic potential are then deduced, with integral constants determinable from the boundary conditions. The analytical solution is derived for beam with material coefficients varying exponentially along the thickness, while the semi-analytical solution is sought by making use of the sub-layer approximation for beam with an arbitrary variation of material parameters along the thickness. The present analysis is applicable to beams with various boundary conditions at the two ends. Two numerical examples are presented for validation of the theory and illustration of the effects of certain parameters.

Output pressure and efficiency of electrokinetic pumping of non-Newtonian fluids

Abstract: Theoretical expressions of the flow rate, output pressure and thermodynamic efficiency of electrokinetic pumping of non-Newtonian fluids through cylindrical and slit microchannels are reported. Calculations are carried out in the framework of continuum fluid mechanics. The constitutive model of Ostwald-de Waele (power law) is used to express the fluid shear stress in terms of the velocity gradient. The resulting equations of flow rate and electric current are nonlinear functions of the electric potential and pressure gradients. The fact that the microstructure of non-Newtonian fluids is altered at solid–liquid interfaces is taken into account. In the case of fluids with wall depletion, both the output pressure and efficiency are found to be several times higher than that obtained with simple electrolytes under the same experimental conditions. Apart from potential applications in electrokinetic pumps, these predictions are of interest for the design of microfluidic devices that manipulate non-Newtonian fluids such as polymer solutions and colloidal suspensions. From a more fundamental point of view, the paper discusses a relevant example of nonlinear electrokinetics.

Combined effect of Debye plasma environment and external electric field on hydrogen atom

Abstract: We consider weakly coupled plasmas, characterized by Debye-Huckel model potential, and an external electric field along z-axis. Due to plasma environment the energy levels of atom are shifted up, bound states are merged to continuum. For external electric field the excited energy levels also split up; degenerate energy eigenvalues become nondegenerate. In the presence of external electric field, energy levels are shifted up and down, except ground state. The ground state energy value is shifted only down. Therefore, it is very interesting to study the combined effect of plasmas and external electric field on a simple atom (hydrogen). To calculate the energy levels and the corresponding states, we expand the wave function in terms of linear combination of the basis functions. The basis is generated by hydrogenic wave functions. Here, we estimate various plasma surroundings and electric field strengths. We observe converged results for the basis size 45, with angular momentum states up to eight.

Modeling of a negative ion source. III. Two-dimensional structure of the extraction region

Abstract: The self-consistent production and transport of H− in the extraction region of a hybrid negative ion source is modeled by means of a two-dimensional particle-in-cell/Monte Carlo simulation. The normal coordinate and one parallel coordinate with respect to the plasma grid are considered to analyze the transport of negative ions. Results show that, in order to establish space charge compensation, the extraction of surface-produced negative ions is limited by the flux of positive ions directed toward the plasma grid surface. An electrostatic barrier appears just in front of the wall, reflecting the majority of surface-produced H− and reducing by this their extraction probability to only 8.5%. Results reproduce the experimentally observed influence of the plasma grid bias voltage on the extraction identifying as a key element the presence of a saddle point in the electric potential distribution.