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Numerical results on the implementation of a computationally efficient algorithm for finding the instantaneous photocurrent across the gap volume in Photoconductive antennas (PCAs) through solution of one-dimensional (1D) drift-diffusion equations along the bias field lines are presented. Excellent agreement with a reference two-dimensional (2D) numerical algorithm is found and the relative error is seen to decrease with the number of lines used in the computation. © 2022 IEEE.

Magnetostriction of ferrogels based on physical and chemical networking with embedded strontium hexaferrite particles was studied in 420 mT uniform magnetic field. Ferrogel with physical networking was based on natural polysaccharide - guar gum, which gelates due to formation of H-bonds. Ferrogel with chemical networking was synthesized by radical polymerization of acrylamide. Magnetostriction of the physical ferrogel resulted in the increase of length of the gel specimen along the field lines and in the proportional decrease of its width in the direction across the field lines. In case of chemical ferrogel, both the length and the width increased in the uniform magnetic field leading to the increase of the ferrogel volume. © Published under licence by IOP Publishing Ltd. Russian Science Foundation, RSF: 18-19-00090 The work was performed under financial support from Russian Science Foundation grant 18-19-00090.

International audience; Determining the partial discharge (PD) inception voltage (PDIV) is a key point when designing electrical coils or busbars. In this paper, a method making it possible to calculate the PDIV as well as to locate PDs in windings of any shape is presented. It is based on a 2-D finite-element computation using both dual-i.e., scalar and vector potential-electrostatic formulations and a comparison of the obtained operating points with Paschen's curve.

We derive a closed-form quasi-static model for the coupling impedance between aligned coplanar rectangular contacts on bulk and epitaxial semiconductor substrates by resolving the 3-D field lines into simpler components (vertical, lateral, fringing, 2-D, etc.). Both insulating and conducting (grounded or floating) backplane conditions are considered. Our model reflects all the geometry and process parameters, and its constants are process independent and universal. The model also gives the capacitive coupling via ambient, i.e., via the region outside the substrate, and specifies conditions under which a given thickness or lateral extension of the substrate can be regarded as infinite. Comparisons with technology computer-aided design simulations and measurements validate the model over a wide range of width/length and width/separation ratios of the contacts. � 2012 IEEE.

Ambient field refers to the field lines outside the semiconductor that are caused by the potential difference between points on the semiconductor. We present a TCAD study of the effects of the ambient field on the IV characteristics of NanoWire (NW) resistors and junctions. The study covers different contact geometries, hilo as well as pn junctions, and practical bias range including the equilibrium condition; effects of varying the wire radius, length, doping and ambient dielectric constant are brought out. The NWs studied have radii?15 nm and length?500 nm for which classical models based on driftdiffusion transport are applicable. Simple qualitative explanations for various non-linear shapes of the IV characteristics are provided using field lines. An appealing analogy is presented for the rise in the carrier concentration of an undoped NW grown on a heavily doped substrate. The study is aimed at improving the understanding of nanoscale devices and proper interpretation of their experimental data. � 2011 Elsevier B.V.

Context. Magnetohydrostatic (MHS) equilibria are often used to model astrophysical plasmas, for example, planetary magnetospheres or coronae of magnetized stars. However, finding realistic three-dimensional solutions to the MHS equations is difficult, with only a few known analytical solutions and even finding numerical solution is far from easy. Aims. We extend the results of a previous paper on three-dimensional solutions of the MHS equations around rigidly rotating massive cylinders to the much more realistic case of rigidly rotating massive spheres. An obvious application is to model the closed field line regions of the coronae of rapidly rotating stars. Methods. We used a number of simplifying assumptions to reduce the MHS equations to a single elliptic partial differential equation for a pseudo-potential U, from which all physical quantities, such as the magnetic field, the plasma pressure, and the density, can be derived by differentiation. The most important assumptions made are stationarity in the co-rotating frame of reference, a particular form for the current density, and neglect of outflows. Results. In this paper we demonstrate that standard methods can be used to find numerical solutions to the fundamental equation of the theory. We present three simple different cases of magnetic field boundary conditions on the surface of the central sphere, corresponding to an aligned dipole field, a non-aligned dipole field, and a displaced dipole field. Our results show that it should be possible in the future to use this method without dramatically increasing the demands on computational resources to improve upon potential field models of rotating magnetospheres and coronae.

Accurately interpreting three dimensional (3D) vector quantities output as solutions to high-resolution computational fluid dynamics (CFD) simulations can be an arduous, time-consuming task. Scientific visualization of these fields can be a powerful aid in their understanding. However, numerous pitfalls present themselves ranging from computational performance to the challenge of generating insightful visual representations of the data. In this paper, we briefly survey current practices for visualizing 3D vector fields, placing particular emphasis on those data arising from CFD simulations of turbulence. We describe the capabilities of a vector field visualization system that we have implemented as part of an open source visual data analysis environment. We also describe a novel algorithm we have developed for illustrating the advection of one vector field by a second flow field. We demonstrate these techniques in the exploration of two sets of runs. The first comprises an ideal and a resistive magnetohydrodynamic (MHD) simulation. This set is used to test the validity of the advection scheme. The second corresponds to a simulation of MHD turbulence. We show the formation of structures in the flows, the evolution of magnetic field lines, and how field line advection can be used effectively to track structures therein. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Fil: Mininni, Pablo Daniel. Universidad de Buenos Aires; Argentina. National Center for Atmospheric Research; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Lee, Ed. National Center for Atmospheric Research; Estados Unidos Fil: Norton, Alan. National Center for Atmospheric Research; Estados Unidos Fil: Clyne, John. National Center for Atmospheric Research; Estados Unidos

International audience; A numerical method is proposed in order to track field lines of three-dimensional divergence free fields. Field lines are computed by a locally valid Hamiltonian mapping, which is computed using a symplectic scheme. The method is theoretically valid everywhere but at points where the field is null or infinite. For any three dimensional flux conservative field for which problematic points are sufficiently sparse, a systematic procedure is proposed and implemented. Construction of field lines is achieved by means of tracers and the introduction of various Hamiltonians adapted to the "geometrical state" each line or tracer is. The states are artificially defined by an a priori given frame of reference and Cartesian coordinates, and refer to a Hamiltonian which is locally valid at the time step to be computed. This procedure ensures the preservation of the volume (flux condition) during the iteration. This method is first tested with an ABC-type flow. Its benefits when compared to typical Runge-Kutta scheme are demonstrated. Potential use of the method to exhibit "coherent" Lagrangian structures in a chaotic setting is shown. An illustration to the computation of magnetic field lines resulting from a three-dimensional MHD simulation is also provided.

We investigate the effects of ambient field from the gate and drain contacts on the current-voltage characteristics of a vertical nanowire field effect transistor having a lightly doped ungated length near the drain. Such a device is suitable for high voltage (tens of volts) applications. It is shown that the ambient field enhances the carrier concentration and divides the ungated region into gate-controlled and drain-controlled sections, controllable by the drain contact size and bias-voltages. These phenomena have a significant impact on the drain breakdown voltage, saturation voltage, saturation current and output resistance. The effects are established with the help of measured data and numerically calculated current-voltage curves and field lines. � 2011 American Institute of Physics.

Context. Magnetohydrostatic (MHS) equilibria are often used to model astrophysical plasmas, for example, planetary magnetospheres or coronae of magnetized stars. However, finding realistic three-dimensional solutions to the MHS equations is difficult, with only a few known analytical solutions and even finding numerical solution is far from easy. Aims. We extend the results of a previous paper on three-dimensional solutions of the MHS equations around rigidly rotating massive cylinders to the much more realistic case of rigidly rotating massive spheres. An obvious application is to model the closed field line regions of the coronae of rapidly rotating stars. Methods. We used a number of simplifying assumptions to reduce the MHS equations to a single elliptic partial differential equation for a pseudo-potential U, from which all physical quantities, such as the magnetic field, the plasma pressure, and the density, can be derived by differentiation. The most important assumptions made are stationarity in the co-rotating frame of reference, a particular form for the current density, and neglect of outflows. Results. In this paper we demonstrate that standard methods can be used to find numerical solutions to the fundamental equation of the theory. We present three simple different cases of magnetic field boundary conditions on the surface of the central sphere, corresponding to an aligned dipole field, a non-aligned dipole field, and a displaced dipole field. Our results show that it should be possible in the future to use this method without dramatically increasing the demands on computational resources to improve upon potential field models of rotating magnetospheres and coronae. Postprint

The aim of this work is to analyze the electromagnetic induction through three different physical models: by the Maxwell and Faraday law related to the rate of change in the magnetic flux trough a closed circuit, by the Lorentz force acting over a free charge and utilizing the transformation of fields proposed by Einstein in his special theory of relativity and, finally, by Weber's electrodynamics. We identify the conceptual differences between these three models and their consequent implications for the interpretation of the physical reality of the utilized magnitudes.