Electric Induction Fields Research Articles

Influence of the geometrical shape of a prominence and the structure of the coronal magnetic field on the probability of eruption, flare and coronal mass ejection development

The equilibrium conditions of the magnetic flux rope containing the prominence depend on the properties of the surrounding magnetic field in the corona and the geometry of the flux rope itself. The eruption of a prominence is usually associated with a loss of stability in the external magnetic field upon reaching a height above which the decay index of the field exceeds the critical value for the development of eruptive instability. For flux ropes with an axis in the form of a straight line or a circle, the critical value of the decay index of the field lies in the range of 1.0—1.5. Based on extrapolation of the magnetic field into the corona from field measurements in the photosphere, it would be possible to predict the probability of eruption of a particular prominence. However, taking into account the fact that the ends of the magnetic flux rope are rooted in the photosphere and remain fixed due to being frozen into the photospheric plasma significantly affects the critical value of the index and complicates the forecast problem. If the magnetic flux rope retains the shape a segment of a torus in the process of evolution, then the critical value of the decay index for its apex depends on what part of the torus it constitutes, being minimal for approximately half of the torus and having a value significantly less than unity. How the eruption of the flux rope will develop after the loss of equilibrium also depends on what part of the complete torus it constitutes at the moment of the onset of the eruption. Shorter flux ropes accelerate very vigorously, but only for a short time, generating stronger electric induction fields that initiate flare processes. However, the final speed that a short flux rope can achieve during acceleration is less than that of longer flux ropes that accelerate less intensely but for a longer time. The induction effects of the latter are less pronounced, so that they are capable of producing only weak flare-like manifestations. Thus, the eruption of a short prominence, which has gained a relatively low speed, can be stopped at a certain height in the corona without generating a coronal mass ejection. But such a “failed eruption” contributes to the development of flare phenomena. On the contrary, eruptions of longer prominences more often lead to the formation of coronal mass ejections and weak flare manifestations.

Computer homogenization of porous piezoceramics of different ferrohardness with random porous structure and inhomogeneous polarization field

The article is concerned with the homogenization problems, in which the effective moduli of porous piezoceramic composites are determined taking into account the inhomogeneity of the polarization field. The homogenization problems are solved by the finite element method in the framework of the theory of effective moduli and the Hill energy principle using the ANSYS package. To this end, in static problems of electroelasticity, the displacements and electric potential, which are linear in spatial variables, are specified on the boundary of a representative volume to provide constant stress and electric induction fields for a homogeneous reference medium. After solving a set of boundary value problems under different boundary conditions and determining the volume-averaged stress components and the electric induction vector, a complete set of effective moduli for the piezoelectric composite is calculated. A representative volume of the piezocomposite is created in the form of a regular finite element mesh consisting of cubic elements. Pores in the representative volume are assumed to be filled with a piezoelectric material with extremely small moduli. Finite elements with pore properties are selected according to a simple random algorithm. The inhomogeneous polarization field is found by solving an electrostatic problem, in which the polarization process in the representative volume is modeled based on a simplified linear formulation. The local coordinate systems for individual finite elements of the composite matrix are specified by the directions of the polarization vectors. In the following, when solving the problems of electroelasticity, these local coordinate systems associated with the elements of the piezoelectric matrix allow recalculating the material properties according to the formulas of transformation of the tensor components as the coordinate systems rotate. In addition, consideration is given to different models describing the change in the moduli of the material from an unpolarized state to a polarized one as a function of the polarization vector. Computational experiments were carried out for three types of piezoceramics: soft ferroelectric piezoceramics PZT-5H, piezoceramics PZT-4 of medium ferrohardness, and piezoceramics PZT-8 with higher degree of ferrohardness. The dependences of the effective moduli on porosity are compared for different laws of polarization inhomogeneity and different kinds of piezoceramic material of the composite matrix.

Comprehensive numerical characterization of a piezoelectric composite with hollow metallic inclusions using an adaptable random representative volume

This paper investigates a piezoelectric composite made up of a piezoceramic matrix with irregularly scattered random-sized hollow metal inclusions. This composite can be produced using a combination of porous ceramic fabrication methods and microcapsule transfer techniques that were previously utilized to deliver nanoparticle medicines in biomedical applications. The effective material characteristics were computed using a numerical homogenization methodology that included finite element analysis, random representative volume element, perfect contact between distinct phases, special linear boundary conditions, and the Hill–Mandel principle. To imitate the random distribution of inclusions inside a particle-filled composite, the relationship describing the inclusion’s volume fraction was adjusted by adding a regularity coefficient. Thus, a new representative volume was designed to study the effect of the non-uniform distribution of randomly sized inclusions on the effective coefficients of the composite. An analysis of the effective properties of this new composite system with metalized pores surfaces (SMPS) revealed the following features. Due to the presence of metallic impurities, the resulting electric induction field or mechanical stress field inside the piezoelectric phase is scattered, which raises the transverse piezoelectric moduli with the increase of the inclusion’s volume fraction. Also, the electrical permittivity coefficients increase steadily with the increase in the portion of the metallic impurities. According to the findings, the volume fraction of the inclusion can be considered the most critical parameter to modify the electromechanical characteristics of the SMPS. The effects of the regularity coefficient on the equivalent properties increase as the inclusion’s volume fraction increases. The effective dielectric constants decrease as the degree of regularity of the composite structure grows, increasing the effectiveness of the piezoelectric transducer in transverse energy harvesting and motor applications. The findings of the newly constructed representative volume were verified using a basic periodic unit-cell and a random representative volume based on the random sequential adsorption (RSA) method. The developed structure of the representative volume can be applied to simulate a wide range of composites in the form of solid particles. Piezoelectric transducers constructed from the proposed piezocomposite are predicted to function well in piezoelectric motors and transverse piezoelectric sensors.

Electro-magnetostriction under large deformation : Modeling with experimental validation

Electro-magneto-elasticity plays a vital role in the advancement of material science. In line with that in the present paper, we model an electro-magnetostriction phenomenon of smart material based on the theory of electro-magneto-elasticity. We adopt a unified classical continuum mechanics approach to model the electro-magnetostriction phenomenon under large deformation. We drive the constitutive relations followed by the second law of thermodynamics with an amended energy density function. The stress field, electric induction field, and the magnetic induction field are obtained through an amended energy density function. We develop the theoretical models of electrostriction and magnetostriction phenomena including the electrostrictive and magnetostrictive effects, which are generally neglected in the existing literature. Additionally, we propose a new amended energy density function for a class of an incompressible isotropic smart material. Finally, we compare and validate the accuracy of the developed theoretical models with their corresponding experimental data.

Cosmic supercollider

This paper presents a model in which a supermassive black hole surrounded by a superstrong magnetic field of up to~ c4G–1.5M–1 ≈ 2 × 1010M9–1G appears as a result of the evolution of galactic nuclei (M9 = M/109 M⊙). In this model, an electric induction field can accelerate particles with positive and negative charges Z up to an energy of ~ec2G–0.5 Z≈1018 Z GeV. Comparison with observational data is discussed.

Nonexistence of smooth electromagnetic fields in nonlinear dielectrics. I. Infinite cylindrical dielectrics

Coupled nonlinear wave equations are derived for the evolution of the components of the electric induction field D in a class of rigid nonlinear dielectrics governed by the nonlinear constitutive relation E = λ( D) D, where E is the electric field and λ [gt] 0 is a scalar-valued vector function. For the special case of an infinite one-dimensional dielectric rod, it is shown that, under relatively mild conditions on λ, solutions of the corresponding initial value problem for the electric induction field cannot exist globally in time in the L 2 sense if it is assumed that the electric field in the rod is perpendicular to the axis of the rod and varies with the coordinate along that axis. The results hold when the electromagnetic field in the rod has compact support. Growth estimates for solutions, which are valid on the maximal time-interval of existence are also derived; these are valid in the simple but physically important case where λ( D) = λ 1 + λ 0 ∥ D ∥ 2. Relations with recent work on the phenomena of self-focusing and self-trapping for high intensity laser beams in a dielectric medium are also discussed.

Asymptotic bounds for solutions to a system of damped integrodifferential equations of electromagnetic theory

Abstract : For the system of damped integrodifferential equations which govern the evolution of the electric induction field in a class of rigid holohedral isotropic dielectrics of the type introduced by Toupin and Rivlin, conditions on the memory functions are deduced which imply that the L2 norms of such induction fields are bounded away from zero even as the damping grows in an unbounded manner; explicit lower bounds for the L2 norms of the induction fields in such dielectrics are derived as t increases without limit. (Author)

Radio-Noise Elimination in Military Aircrart

RADIO noise may be defined as radio-frequency energy which interferes with the reception of desired signals. This interference can be the result of: 1. Atmospheric electrical discharges which result in radiated radio frequency energy. 2. Periodic corona discharges from the airplane which cause intense electric induction fields close to the receiving antennas. 3. Receiver internal noise due to thermal agitation in the receiver input resistance and shot effect in the low-level radio-frequency stages.1 4. Electrical transients which result from the operation of electrical equipment.

Radio-noise elimination in military aircraft

RADIO noise may be defined as radio-frequency energy which interferes with the reception of desired signals. This interference can be the result of: 1. Atmospheric electrical discharges which result in radiated radio frequency energy. 2. Periodic corona discharges from the airplane which cause intense electric induction fields close to the receiving antennas. 3. Receiver internal noise due to thermal agitation in the receiver input resistance and shot effect in the low-level radio-frequency stages. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> 4. Electrical transients which result from the operation of electrical equipment.