External Current Density Research Articles

Stationary and nonstationary models of the global electric circuit: Well-posedness, analytical relations, and numerical implementation

We analyze the formulation of the problem of global atmospheric electric circuit modeling. It was shown that under some relatively simple and widely used simplifying assumptions this problem can be reduced to finding the temporal and spatial dependencies of the electric potential on the specified generators, which are determined by the external electric current density. They correspond to thunderclouds in the real atmosphere. The ionospheric potential (the potential difference between the upper and lower atmospheric boundaries) is not specified explicitly but can be uniquely determined from the solution. The formulations of the stationary and nonstationary problems are given in terms of the potential and their well-posedness is discussed. We obtained a number of analytical relations under some restrictions on the distribution of conductivity. They include the formulas which explicitly express the ionospheric potential in terms of the problem parameters. The examples of numerical calculations using the software developed on the basis of general formulations of the stationary and nonstationary problems are demonstrated.

Kinetic Model for Anode of a Direct Carbon Fuel Cell

The Direct Carbon Fuel Cell (DCFC), which uses solid carbon as fuel and molten carbonate as electrolyte, has had resurgence of interest due to very high electrochemical conversion efficiency (nearly 100%), no requirement of fuel reforming, and potential for CO2 capture and sequestration. At the cathode, carbon dioxide is converted into carbonate ions. The main reaction at the anode is generation of carbon dioxide from carbon and carbonate, viz.,(1) C + 2CO3 2- = 3CO2 + 4e-.The net cell reaction is oxidation of carbon to carbon dioxide. Additional reactions that may occur at the anode are (i) a two-electron reaction resulting in co-generation of carbon dioxide and carbon monoxide, viz.,(2) C + CO3 2- = CO2 + CO + 2e-,and (ii) the Boudouard reaction leading to conversion of carbon and carbon dioxide to carbon monoxide, viz.,(3) C + CO2 = 2CO2,the so-called “carbon corrosion” reaction. The performance of DCFC can be appreciably limited by this reaction.A one-dimensional macro-homogeneous kinetic model for a DCFC anode is developed in this study. We consider steady-state operation of a DCFC with uniform distribution of carbon and molten carbonate in the anode. The potential drop through the anode current collector, placed usually near the anode-electrolyte interface, is considered to be negligible. Given their small size, carbon particles are fully wetted in molten carbonate and the extent of the reverse Boudouard reaction is therefore negligible. For the characteristic pore diameters considered, there is substantial over-pressure in the thick slurry comprised of carbon particles and molten carbonate, permitting the reaction products to remain dissolved in the electrolyte. The reaction products are transported through the anode until they leave via gas channel at one end of the anode. In the thick slurry, the dominant mechanism for this transport is diffusion. The rates of reactions (1) and (2) are described by concentration- and temperature-dependent Butler-Volmer rate expressions. Each reaction is inhibited by its product(s).The conservation equations for electronic and ionic potentials are related to each other due to electro-neutrality. This is also the case with the conservation equations for electronic and ionic currents. The conservation equations for carbon monoxide and carbon dioxide are based on Fick’s law of diffusion. Numerical effort in solution of the four conservation equations can be reduced considerably by recognizing that only two of these are independent, as there are only two independent reactions. One therefore needs to solve only two boundary-value problems to determine the profiles of electronic potential, ionic potential, electronic current, ionic current, and product concentrations. The boundary conditions for the four variables depend on the configuration of a DCFC and location of the current collector in the anode, its distance from the anode-electrolyte interface. The external current density I is specified. The base values of the system parameters were obtained using information available in the published literature.Various microstructure and macrostructure parameters influence design and performance of a DCFC anode and these are considered in the model. Appropriate dimensionless parameters and variables are used to reduce the number of system parameters and variables via lumping. Five of the dimensionless parameters provide binary comparisons of resistances for reactions (1) and (2), ohmic resistance, and resistances for transport of the two reaction products. Various sets of the five dimensionless parameters are considered to examine the distribution of electronic and ionic potentials, electronic and ionic current densities, rates of reactions (1) and (2), and concentrations of carbon monoxide and carbon dioxide. Conditions under which reactions (1) and (2) occur throughout the anode, corresponding to a very effective anode, are identified. Conditions under which this is not the case are also investigated to see if there are specific benefits in constraining the two reactions to portion(s) of the anode. Besides generating spatial profiles of system variables for the anode, the kinetic model enables identification of polarization curves and power density versus current density plots. The optimum current density and the corresponding power density are influenced strongly by the relative importance of the five resistances. The effect of location of the anode current collector with respect to the anode-electrolyte interface is examined via few model simulations.

Effect of copper metalation of tetrabenzoporphyrin donor material on organic solar cell performance

The effects of copper metalation of tetrabenzoporphyrin on the properties and performance of organic solar cells are studied. Tetrabenzoporphyrin (BP) and copper tetrabenzoporphyrin (CuBP) are both solution processed from soluble precursor materials and thermally converted in the thin film. Despite high field-effect hole mobility above 1 cm2 V−1 s−1, the power conversion efficiency (PCE) of solar cell devices with CuBP is severely diminished compared to those with BP. Conducting atomic force microscopy (c-AFM) is used to show that CuBP films are highly conductive in the direction perpendicular to the substrate, relative to those comprising BP. By analyzing the donor absorption characteristics as well as the external quantum efficiency and short-circuit current density of bilayer OPV devices as a function of donor layer thickness, it is determined that the differences in performance are likely due to a prohibitively short effective exciton diffusion length (LD) in the metalated derivative. By modeling the external quantum efficiency of bilayer OPV devices, we are able to approximate this difference in effective LD to be 15 nm for BP and 2 nm for CuBP.

Electrochemical oxygen separation using hydroxide ion conductive layered double hydroxides

Abstract This paper reports a novel electrochemical oxygen separation process using a hydroxide ion conductor as an electrolyte. In this study, we used Ni–Fe layered double hydroxide (LDH) intercalated with CO 3 2 − (Ni–Fe CO 3 2 − LDH) as a hydroxide ion conductive material. Ni–Fe CO 3 2 − LDH was prepared using the co-precipitation method. Electrodes using Pt/C as a catalyst and Ni–Fe CO 3 2 − LDH as an ionomer were prepared and a membrane reactor for oxygen separation using Ni–Fe CO 3 2 − LDH as an electrolyte was fabricated. The electrochemical oxygen product flow was confirmed to be proportional to the external current density, and thus the membrane functioned at 50 °C under 70% of relative humidity and an electrical potential gradient.

Electrical Double Layer Model and Thermodynamic Coupling for Electrochemically Deposited Hydrogenated Amorphous Carbon Films

In this study, the growth mechanism for electrodeposition of hydrogenated amorphous carbon (a-C:H) films was discussed from two novel perspectives. First an electrical double layer is considered to form in the vicinity of the electrodes. The double layer is believed to govern the variation tendency of the external current density. Then by introducing a concept called thermodynamic coupling we have explained the growth mechanism of a-C:H films from liquid phase electrodeposition and pointed out that hydrogen atoms play a crucial role in lowering applied voltage. Related experiments are conducted to corroborate our opinion.

Spin-Torque Effect on Thermally Excited Magnetization Fluctuation Noise in Tunneling Magnetoresistive Read Heads

The spin-torque (ST) effect on the thermally excited magnetization fluctuation noise (thermal mag-noise) in tunneling magnetoresistive (TMR) read heads is investigated in the GHz range using noise spectra. The strong noise spectral peak around 3.1 GHz is attributed to thermal mag-noise originating from the free layer. The peak intensity and linewidth strongly depend on both the external magnetic field and current density. These features demonstrate that the ST effect significantly influences the thermal mag-noise as the current density increases up to the critical current density. Additionally, it is speculated that the non-thermal fluctuation noise originating from ST in the TMR heads as well as in current perpendicular to plane giant magnetoresistive (CPP-GMR) heads is generated above a critical current of approximately 2.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> A/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Improvement in open circuit voltage of organic solar cells by inserting a thin phosphorescent iridium complex layer

The authors develop organic solar cells (OSCs) with a multicharge separation (MCS) interface by inserting ∼4 nm thin layer of phosphorescent bis(2-(4-tertbutylphenyl) benzothiazolato-N,C2,) iridium (acetylacetonate) (t-bt)2Ir(acac) comparing with copper phthalocyanine (CuPc) between pentacene/C60 heterojunction. The result showed that open circuit voltage is remarkably enhanced without obviously changing external quantum efficiency ηEQE and short-circuit current density. As a result, power conversion efficiency is improved from 1.53% for pentacene/C60 device to 1.83% with sandwich layer (t-bt)2Ir(acac) and 1.98% with CuPc. Moreover, a suitable equivalent circuit model is proposed to intuitively reveal the inner photogeneration process of OSC with MCS interface.

Resistance Reduction Induced by Small Electric Current in CoCu Porous Films

The ferromagnetic CoCu porous films were prepared by electrochemical deposition based on the double layered colloidal template on indium tin oxide-coated glass substrates. The investigation of electrics discovered that resistance reduction could be induced by a small electric current in these ferromagnetic porous films. For fixed current density, the resistance decreased: from initial state value to steady state one, it was smaller at high magnetic field than that at low field. For a fixed magnetic field, a smaller current density led to longer relaxation time. The resistance reduction value and relaxation time can be controlled by the external magnetic field and current density. A possible model of the current-driven movement of domain walls in low current density is proposed to explain reduction behaviors in such CoCu porous film and this will have highly valuable applications in magnetic delay switches.

10.1007/s11470-008-2010-6

The initial-boundary value problem of determining the electromagnetic field in an inhomogeneous conducting sample and the surrounding external medium is solved under certain assumptions on the sample, the external medium, and the external current density. The existence of a classical solution to this problem is proved. The electromagnetic field under small variations in the sample’s electric conductivity is computed by applying perturbation theory.

Effects of scan rate on the potentiodynamic polarization curve obtained to determine the Tafel slopes and corrosion current density

Effects of charging current on the potentiodynamic polarization curve that is obtained to determine the Tafel slopes and corrosion current density are reported in this paper. The potentiodynamic polarization curves are obtained at different scan rates for Ti6Al4V in naturally aerated 3.5% NaCl solution. The results show that the potential where the external current density equals to zero does not equal to the open circuit potential. The extent of the distortion of the polarization curve can be reflected the difference between the two potentials. Some significant errors are introduced into the values of the corrosion current density and Tafel slopes due to this distortion. In addition, severe distortion of the polarization curve can lead to misunderstanding of the electrode process. A new method is adopted to eliminate this distortion, and the potential-dependent of charging current density can also be obtained.

Initial-boundary value problem and integrodifferential equations of electrodynamics for an inhomogeneous conductive body

The initial-boundary value problem of determining the electromagnetic field in an inhomogeneous conducting sample and the surrounding external medium is solved under certain assumptions on the sample, the external medium, and the external current density. The existence of a classical solution to this problem is proved. The electromagnetic field under small variations in the sample’s electric conductivity is computed by applying perturbation theory.

Room temperature performance of low threshold 1.34-1.44-/spl mu/m GaInNAs-GaAs quantum-well lasers grown by molecular beam epitaxy

Room temperature lasing emission at 1.338 and 1.435 μm with threshold current densities of 1518 and 1755 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, is obtained in broad area GaInNAs-GaAs laser diodes (LDs) grown by molecular beam epitaxy. The 1.338-μm LDs show a power output per facet up to 0.20 W/A, a characteristic temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) of 78 K, and an external transparency current density (J/sub tr/) of 0.77 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Increasing the lasing wavelength to 1.435 μm results in a larger J/sub tr/ of 1.16 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a lower T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> of 62 K, due to larger nonradiative recombination. However, the 1.435-μm LDs still display a power output per facet up to 0.15 W/A, and a high internal quantum efficiency of 52%. These improved performances are achieved without the need to use strain compensation layers, Sb as a surfactant during the quantum-well growth, or a postgrowth thermal anneal cycle.

Study of enhanced light scattering in microcrystalline silicon solar cells

Effects of an enhanced haze parameter and the angular distribution function of scattered light are analyzed in a single-junction microcrystalline silicon solar cell by means of optical modeling. Hypothetical high haze parameters and different angular distribution functions are introduced to study the role of efficient light trapping. Improvements in external quantum efficiency and short-circuit current density of the solar cell are predicted. Potential thickness reductions of the absorber layer are calculated.

Optical modelling of thin-film silicon solar cells deposited on textured substrates

Optical modelling is used to investigate effects of light scattering in amorphous silicon and microcrystalline silicon solar cells. The role of enhanced haze parameter and different angular distribution function of scattered light is analyzed. Results of optical simulation show that enhanced haze parameter compared to that of Asahi U-type SnO 2:F does not improve external quantum efficiency and short-circuit current density of amorphous silicon solar cell significantly, whereas for microcrystalline silicon solar cell the improvement is larger. Angular distribution function affects the external quantum efficiency and the short-circuit current density significantly.

The force-free case in three-dimensional superconductors: a computational study

Abstract We investigate the formation and motion of vortices in a three-dimensional cylindrical superconductor using a computer simulation which solves the relevant Ginzburg-Landau equations. We look particularly at the case of a cylindrical superconductor with an external current density and magnetic field applied in the direction of the cylinder axis. The magnetic field lines which result from the applied current density are circular and perpendicular to the applied field lines. Two types of competing vortex form which tend to become twisted, causing the vortices to be pinned by each other up to a critical current density. We show snapshot pictures illustrating the vortex behaviour in this case just above and below Jc and also comment on the formation of vortices at very high current densities.

Computation of magnetic fields within source regions of ionospheric and magnetospheric currents

A general method of computing the magnetic effect caused by a predetermined three-dimensional external current density is presented. It takes advantage of the representation of solenoidal vector fields in terms of toroidal and poloidal modes expressed by two independent series of spherical harmonics. In order to test the method, it is applied to two ionospheric–magnetospheric model current densities. The first example assumes a special large-scale current system which has an analytical solution for the magnetic field everywhere. In the second example, the results for a model current distribution that is of small-scale at high latitudes are compared with a direct integration using Biot–Savarts law. It is demonstrated that the method provides a fast and numerically stable determination of the magnetic field both outside and inside the current density.

The electrochemical corrosion of pure magnesium in 1 N NaCl

An electrochemical investigation was carried out to study the corrosion of pure magnesium in l N NaCl at different pH values involving electrochemical polarisation, scanning tunnel microscopy (STM), measurement of hydrogen gas evolution and measurement of the elements dissolved from the magnesium specimen which were determined by inductively coupled plasma atomic emission spectrophotometry (ICPAES). A partially protective surface film was a principal factor controlling corrosion. Film coverage decreased with increasing applied electrode potential. Application of a suitable external cathodic current density was shown to inhibit magnesium dissolution whilst at the same time the hydrogen evolution rate was relatively small. This showed that cathodic protection could be used to significantly reduce magnesium corrosion. A new definition is proposed for the negative difference effect (NDE).

Spatially resolved analysis and minimization of resistive losses in high-efficiency Si solar cells

This paper presents an improved method for measuring the total lumped series resistance (Rs) of high-efficiency solar cells. Since this method greatly minimizes the influence of non-linear recombination processes on the measured Rs values, it is possible to determine Rs as a function of external current density over a wide range of illumination levels with a significantly improved level of accuracy. This paper furthermore explains how resistive losses in the emitter, the base, the metal/silicon contacts and the front metal grid can be separately determined by combining measurements and multidimensional numerical simulations. A novel combination of device simulation and circuit simulation is introduced in order to simulate complete 2 × 2 cm2 PERL (‘passivated emitter and rear locally-diffused’) silicon solar cells. These computer simulations provide improved insight into the dynamics of resistive losses, and thus allow new strategies for the optimization of resistive losses to be developed. The predictions have been experimentally verified with PERL cells, whose resistive losses were reduced to approximately half of their previous values, contributing to a new efficiency world record (24.0%) for silicon solar cells under terrestrial illumination. The measurement techniques and optimization strategies presented here can be applied to most other types of solar cells, and to materials other than silicon.

Magnetization and impedance of an inductively coupled metal sphere

Magnetization and impedance of an electrically conducting sphere, which is inductively coupled with an arbitrary, sinusoidally alternating current density distribution, are calculated analytically. The general results are applied to the special case, where the external current density distribution is concentrated on thin, toroidal rings surrounding the spherical sample. Measurements of the impedance can be used for a contactless determination of the electrical conductivity. This problem is addressed in a final section.

Force and torque of an electromagnetically levitated metal sphere

The Lorentz force and torque exerted on an electrically conducting sphere exposed to an external, time-varying magnetic field are analytically calculated. The external magnetic field is generated by a set of sinusoidally alternating, but otherwise arbitrary, current density fields of different frequencies and phases. Expressions for the force and torque in a laboratory frame of reference, which is more convenient for application, are also given. Finally, the special cases of rotational and mirror-symmetric external current density fields are treated in more detail.