Surface Current Density Research Articles

Long QT2 Mutation on the Kv11.1 Ion Channel Inhibits Current Activity by Ablating a Protein Kinase Cα Consensus Site

Mutations that inhibit Kv11.1 ion channel activity contribute to abnormalities of cardiac repolarization that can lead to long QT2 (LQT2) cardiac arrhythmias and sudden death. However, for most of these mutations, nothing is known about the molecular mechanism linking Kv11.1 malfunction to cardiac death. We have previously demonstrated that disease-related mutations that create consensus sites for kinases on ion channels can dramatically change ion channel activity. Here, we show that a LQT2-associated mutation can inhibit Kv11.1 ion channel activity by perturbing a consensus site for the Ser/Thr protein kinase C α (PKCα). We first reveal by mass spectrometry analysis that Ser890 of the Kv11.1 ion channel is phosphorylated. Then, we demonstrate by a phospho-detection immunoassay combined with genetic manipulation that PKCα phosphorylates Ser890. Furthermore, we show that Ser890 phosphorylation is associated with an increase in Kv11.1 membrane density with alteration of recovery from inactivation. In addition, a newly discovered and as yet uncharacterized LQT2-associated nonsynonymous single nucleotide polymorphism 2660 G→A within the human ether-á-go-go-related gene 1 coding sequence, which replaces arginine 887 with a histidine residue (R887H), strongly inhibits PKCα-dependent phosphorylation of residue Ser890 on Kv11.1, and ultimately inhibits surface expression and current density. Taken together, our data provide a functional link between this channel mutation and LQT2.

A Three-Dimensional Adaptive Integral Method for Scattering From Structures Embedded in Layered Media

A 3-D extension of the adaptive integral method (AIM) is presented for fast analysis of scattering from electrically large perfect electrically conducting structures embedded inside a single layer of a planar layered medium. The proposed scheme accelerates the iterative method-of-moments (MOM) solution of the combined-field integral equation by employing a 3-D auxiliary regular grid. It uses the auxiliary grid to execute the standard four-stage AIM procedure; unlike the procedure for free space, two different sets of matrices are obtained for the AIM propagation stage by decomposing the Green functions to terms that are in convolution or correlation form in the stratification direction. These matrices are in (three level) block-Toeplitz and Hankel-(two level)-block-Toeplitz forms and can be multiplied by using 3-D FFTs. The dominant computational costs of the scheme are the evaluation of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$O(N)$</tex></formula> different layered-medium Green functions, which is accelerated by extracting asymptotic terms and using interpolation tables, and the matrix multiplications in the propagation stage, which require only <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$O(N_{\rm C}\log N_{\rm C})$</tex></formula> per iteration; these should be contrasted to the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$O(N^{2})$</tex></formula> Green function evaluations and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$O(N^{2})$</tex></formula> operations per iteration required by the classical MOM. Here, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$N_{\rm C}$</tex></formula> denotes the number of nodes on the auxiliary grid, and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$N$</tex></formula> denotes the number of degrees of freedom of the surface current density. Numerical results validate the proposed method's complexity, demonstrate its accuracy for several large-scale structures in layered media, and compare its computational costs to those of its counterpart for free space.

Influence of body parameters on gastric bioelectric and biomagnetic fields in a realistic volume conductor

Electrogastrograms (EGG) and magnetogastrograms (MGG) provide two complementary methods for non-invasively recording electric or magnetic fields resulting from gastric electrical slow wave activity. It is known that EGG signals are relatively weak and difficult to reliably record while magnetic fields are, in theory, less attenuated by the low-conductivity fat layers present in the body. In this paper, we quantified the effects of fat thickness and conductivity values on resultant magnetic and electric fields using anatomically realistic torso models and trains of dipole sources reflecting recent experimental results. The results showed that when the fat conductivity was increased, there was minimal change in both potential and magnetic fields. However, when the fat conductivity was reduced, the magnetic fields were largely unchanged, but electric potentials had a significant change in patterns and amplitudes. When the thickness of the fat layer was increased by 30 mm, the amplitude of the magnetic fields decreased 10% more than potentials but magnetic field patterns were changed about four times less than potentials. The ability to localize the underlying sources from the magnetic fields using a surface current density measure was altered by less than 2 mm when the fat layer was increased by 30 mm. In summary, results confirm that MGG provides a favorable method over EGG when there are uncertain levels of fat thickness or conductivity.

Optimization MRI Cylindrical Coils Using Discretized Stream Function With High Order Smoothness

The design of coil for magnetic resonance image (MRI) application is an optimization problem, in which a specified distribution of the magnetic field inside a region of interest is generated by choosing the optimal distribution of current density on a specified non-intersecting design surface. This paper proposes an iterative optimization method for designing MRI coils on a cylindrical surface by using a piecewise discretized scalar stream function as design variable. The surface current density is accurately calculated using piecewise interpolation with smoothness based on the developable property for a cylindrical surface. MRI coils are designed by choosing bi-objective functions and pseudo-Newton sensitivity analysis. The smoothness of the coil are maintained by adjusting the value of derivative degrees of freedom of design variables which are used to interpolate the stream function. Pareto points provide more flexible choices between the two complementary objectives.

Study on tribological and electrochemistry properties of metal materials in H2O2 solutions

Hydrogen peroxide (H2O2) is a kind of ideal green propellant. It is crucial to study the wear behavior and failure modes of the metal materials under the strong oxidizing environment of H2O2. This study aims to investigate the wear of rubbing pairs of 2Cr13 stainless steel against 1045 metal in H2O2 solutions, which has a great effect on wear, the decomposition and damage mechanism of materials. The comparison analysis of the friction coefficients, wear mass loss, worn surface topographies and current densities was conducted under different concentrations of H2O2 solutions. There were significant differences in the tribological and electrochemistry properties of the rubbing pairs in different H2O2 solutions.

An analytical technique to fast evaluate mutual coupling integrals in spectral domain analysis of multilayered coplanar coupled striplines

The analysis of propagation in multilayered coplanar coupled striplines by means of Galerkin's method in the spectral domain with expansion functions factorizing the edge behavior of the surface current density on each strip leads to the evaluation of slowly converging integrals. In this work a new analytical technique to express the mutual coupling integrals as rapidly converging series is presented. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1035–1039, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26674

Correction to “Radio Frequency Interference and Lightning Studies of a Square Kilometer Array Demonstrator Structure” [May 2011

We studied computational electromagnetic and scale models of a Square Kilometer Array demonstrator structure in our paper listed above (ibid., vol. 53, no. 2, pp. 543-547, May 2011). During the final publication process, one of our figures was inadvertently duplicated and the pivotal point of the paper was lost. The omitted numerical simulation would have illustrated the value of the optimized lightning down conductor (LDC). Fig. 1 here (intended [Fig. 10 in the above paper]) should be compared to Fig. 2 ([above paper, Fig. 11]). The considerably lower surface current density acheived due to the LDC reconfiguration was the purpose of the above listed work.

Mixed discretization schemes for electromagnetic surface integral equations

In developing accurate and stable discretization schemes for integral equations, important steps are the choices of the basis and testing functions. In the electromagnetic surface integral equations, the unknown quantities, the equivalent electric and magnetic surface current densities, are by default divergence conforming and therefore should be expanded with the divergence‐conforming basis functions. The choice of the testing functions however is less obvious and depends on the choice of the basis functions and the properties of the integral operators. We develop stable and well‐defined discretization procedures where the operators are tested either their range or on the dual of their range. This requires the use of non‐conventional finite‐elements spaces, called ‘dual spaces’, and non‐traditional testing procedures. We show with numerical examples that in most cases, testing the operators on the dual of their range leads to improved solution accuracy compared with testing the operators on their range. For the integral equations of the first kind, this agrees with the conventional Galerkin's scheme, but for the integral equations of the second kind, this requires the use of Petrov–Galerkin type discretization schemes with appropriate curl‐conforming (dual) testing functions. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Radar Cross-Section Formulation of a Shell-Shaped Projectile Using Modified PO Analysis

A physical optics based method is presented for calculation of monostatic Radar Cross-Section (RCS) of a shell-shaped projectile. The projectile is modeled using differential geometry. The paper presents a detailed analysis procedure for RCS formulation using physical optics (PO) method. The shortcomings of the PO method in predicting accurate surface current density near the shadow boundaries are highlighted. A Fourier transform-based filtering method is proposed to remove the discontinuities in the approximated surface current density. The modified current density is used to formulate the scattered field and RCS. Numerical results are presented comparing the proposed method with conventional PO method. The results are also compared with published results of similar objects and found to be in good agreement.

TM Scattering by Perfectly Conducting Polygonal Cross-Section Cylinders: A New Surface Current Density Expansion Retaining up to the Second-Order Edge Behavior

In the analysis of scattering by perfectly conducting cylinders with polygonal cross-section by means of surface integral operator formulations, fast convergence can be achieved by expanding the surface current density on each side with basis functions factorizing the correct behavior of the fields on the wedges. Usually, the factorized edge behavior is chosen to be coincident with the first order behavior prescribed by Meixner's theory. However, it could not be the correct one and, consequently, the convergence of the method becomes increasingly slow as the theoretical behavior differs from the real one. This phenomenon is particularly notable when one or more of the predicted singularities unexpectedly disappear. To overcome this problem, in this work the analysis of TM scattering is made by introducing a new expansion devised so that only the first two terms are responsible for the reconstruction of the singularities while the remaining part of the expansion factorizes the second order edge behavior. Actually, the proposed expansion outperforms the one introduced by the authors in a previous work factorizing the first order edge behavior even when this is the correct one.

Can Radiators Be Really Isotropic?

In search for isotropic radiators with reasonable quality Factor (Q), bandwidth, and efficiency, one looks for practical radiators with a typical resonant length of . We present here a Green's function analysis in Fourier of a microstrip element and a far-field integral method in configuration (real) space of single and dual U-shaped elements. Both solutions analytically prove that the power radiation patterns are isotropic in nature (while the thickness and the width tend to zero), although the polarizations are not symmetrical in all cuts. It is also shown that the power isotropic U-shaped radiator, for which the surface current density is infinite, can be replaced by another finite-size radiator, having finite-surface current density, such that its far-field is exactly the same as the far-field of the U-shaped isotropic radiator.

Disruption of Kv1.3 Channel Forward Vesicular Trafficking by Hypoxia in Human T Lymphocytes

Hypoxia in solid tumors contributes to decreased immunosurveillance via down-regulation of Kv1.3 channels in T lymphocytes and associated T cell function inhibition. However, the mechanisms responsible for Kv1.3 down-regulation are not understood. We hypothesized that chronic hypoxia reduces Kv1.3 surface expression via alterations in membrane trafficking. Chronic hypoxia decreased Kv1.3 surface expression and current density in Jurkat T cells. Inhibition of either protein synthesis or degradation and endocytosis did not prevent this effect. Instead, blockade of clathrin-coated vesicle formation and forward trafficking prevented the Kv1.3 surface expression decrease in hypoxia. Confocal microscopy revealed an increased retention of Kv1.3 in the trans-Golgi during hypoxia. Expression of adaptor protein-1 (AP1), responsible for clathrin-coated vesicle formation at the trans-Golgi, was selectively down-regulated by hypoxia. Furthermore, AP1 down-regulation increased Kv1.3 retention in the trans-Golgi and reduced Kv1.3 currents. Our results indicate that hypoxia disrupts AP1/clathrin-mediated forward trafficking of Kv1.3 from the trans-Golgi to the plasma membrane thus contributing to decreased Kv1.3 surface expression in T lymphocytes.

A Selective Ink Deposition Method for the Cost-Performance Optimization of Inkjet-Printed UHF RFID Tag Antennas

A selective ink deposition method is proposed for fabricating inkjet-printed passive UHF RFID tag antennas with optimized cost-performance ratios. The deposition method is based on identifying areas with high surface current densities on a given tag antenna and applying additional silver nanoparticle ink onto such areas to increase tag read range. In this paper, the proposed method is experimentally verified by utilizing the method on a small dipole tag antenna. Several ink deposition schemes are created, and their read range performances and ink consumptions are presented.

An Active Electromagnetic Cloak Using the Equivalence Principle

Electromagnetic cloaking refers to the ability to prevent an object from scattering an incident electromagnetic field. This has been accomplished in recent works by specially designed materials. Another way of cloaking using sources has been known in the acoustics community. In this letter, we introduce a prescription for canceling the electromagnetic scattering of an object by using an array of sources. By using the equivalence principle, we show that by superimposing magnetic and electric surface current densities at the boundary of an object, the scattered fields from that object can be canceled. These magnetic and electric surface currents can be discretized into electric and magnetic dipoles that are physically implementable by straight and loop wire antennas. Finally, we confirm our results using numerical simulations.

Pole discontinuity removal using artificial neural networks for microstrip antenna design

This article presents the use of artificial neural networks for the evaluation of integrals with finite number of pole singularities while formulating the integral equation for the electric surface current density. A feed-forward single-layer back-propagated artificial neural network (ANN) model has been trained to approximate the discontinuous integrand function. Generation of a soft continuous function obtained from the ANN model and closed-loop expressions for the evaluation of the integrals are presented. The proposed technique is applied to compute the input impedance of microstrip antenna and results have been compared with IE3D. Integration has been performed using n-point Gaussian quadrature rule for evaluating the reaction matrix.

A singular integral representation of the electromagnetic field: Physical regularization of the ill-posedness of the near-field zones of antennas

A classification of ill-posedness in the antenna theory is presented in the case when the basic principles of electromagnetics are not fulfilled, which is observed in the near-field radiation zones. The Tikhonov regularization of Fredholm integral equations of the first kind is compared with the physical regularization (a self-consistent method). The ill-posedness arising in the analysis of the electromagnetic field (EMF) of an electric dipole, an equidistant array on its basis, frame antennas, and a cylindrical helical antenna is considered. In particular, for the EMF of an electric dipole, the gap between the field and surface current density is removed and the limits of applicability of the method of induced electromotive forces of coupled dipoles are established. It is shown that unidirectional radiation in the azimuthal plane is typical of a ring frame antenna with a certain dimension of the ring. For a cylindrical helical antenna, the calculation of the surface current density is reduced to a hypersingular integral equation with a quadratic Cauchy singularity. The analysis of the behavior of the current flowing along the helix made it possible to explain the peculiarities of the antenna pattern for various helical turns.

Wave scattering from random sets of closely spaced objects through linear embedding via Green's operators

In this paper we present the application of linear embedding via Green's operators (LEGO) to the solution of the electromagnetic scattering from clusters of arbitrary (both conducting and penetrable) bodies randomly placed in a homogeneous background medium. In the LEGO method the objects are enclosed within simple-shaped bricks described in turn via scattering operators of equivalent surface current densities. Such operators have to be computed only once for a given frequency, and hence they can be re-used to perform the study of many distributions comprising the same objects located in different positions. The surface integral equations of LEGO are solved via the Moments Method combined with Adaptive Cross Approximation (to save memory) and Arnoldi basis functions (to compress the system). By means of purposefully selected numerical experiments we discuss the time requirements with respect to the geometry of a given distribution. Besides, we derive an approximate relationship between the (near-field) accuracy of the computed solution and the number of Arnoldi basis functions used to obtain it. This result endows LEGO with a handy practical criterion for both estimating the error and keeping it in check.

Localization of endocardial ectopic activity by means of noninvasive endocardial surface current density reconstruction

Localization of the source of cardiac ectopic activity has direct clinical benefits for determining the location of the corresponding ectopic focus. In this study, a recently developed current-density (CD)-based localization approach was experimentally evaluated in noninvasively localizing the origin of the cardiac ectopic activity from body-surface potential maps (BSPMs) in a well-controlled experimental setting. The cardiac ectopic activities were induced in four well-controlled intact pigs by single-site pacing at various sites within the left ventricle (LV). In each pacing study, the origin of the induced ectopic activity was localized by reconstructing the CD distribution on the endocardial surface of the LV from the measured BSPMs and compared with the estimated single moving dipole (SMD) solution and precise pacing site (PS). Over the 60 analyzed beats corresponding to ten pacing sites (six for each), the mean and standard deviation of the distance between the locations of maximum CD value and the corresponding PSs were 16.9 mm and 4.6 mm, respectively. In comparison, the averaged distance between the SMD locations and the corresponding PSs was slightly larger (18.4 ± 3.4 mm). The obtained CD distribution of activated sources extending from the stimulus site also showed high consistency with the endocardial potential maps estimated by a minimally invasive endocardial mapping system. The present experimental results suggest that the CD method is able to locate the approximate site of the origin of a cardiac ectopic activity, and that the distribution of the CD can portray the propagation of early activation of an ectopic beat.

Model for corrosion of metals covered with thin electrolyte layers: Pseudo-steady state diffusion of oxygen

A one-dimensional mathematical model is presented for the free corrosion of a bare metal surface (devoid of any oxide film) under a thin electrolyte layer using mixed potential theory where anodic metal dissolution is controlled by oxygen diffusion through the electrolyte layer and by the oxygen reduction at the metal surface. A pseudo-steady state is considered wherein the oxygen diffusion is at steady state while the metal and hydroxyl ions keep accumulating in the thin electrolyte layer due to a decoupling arising from the assumed Tafel laws for corrosion kinetics. Under free corrosion the oxygen diffusion is shown to depend on a non-linear boundary condition with a non-integer power on oxygen concentration at the metal surface which makes the model non-trivial. Analytical and numerical results for the oxygen concentration at the metal surface, corrosion potential, and corrosion current density are reported which depend on several kinetic, thermodynamic and transport parameters in the system. The model is applied to iron and zinc systems with input data taken from the literature. The experimental utility of the model for gathering thin-film corrosion parameters from a study of the corrosion current and potential as a function of the thickness of the electrolyte layer is discussed. Precipitation and passivity, though not the main object of study in this work, are briefly discussed.

Single-Feed Dual-Band Dual-Linearly-Polarized Proximity-Coupled Patch Antenna

In this paper, two novel single-feed dual-band dual-polarized microstrip antennas, fed by proximity coupling, are presented. The first approach begins with a new patch antenna that provides dual-band dual-polarized operation by means of an open-circuit stub, added at the open end of the feed line. By adding a stub to the end of the feed line, one can make an antenna with two resonant frequencies. The first resonant frequency is approximately the same as that in the initial design, but the second frequency depends on the stub's length, the stub's location, and the location of the feed point across the patch's width. Moreover, the variation of the feed-line location with respect to the patch's length has no significant effect on the first resonance frequency, while the second frequency changes. The second approach that is studied to realize a dual-band dual-polarized design utilizes a microstrip-gap proximity-coupled feed mechanism. Further insight is sought through the investigation of the surface-current densities on the proposed patch antennas at their resonant frequencies. The radiation performance - including radiation pattern, cross polarization, and gain - is satisfactory within two bands. The CST simulation results and measurement results showed good agreement with each other.