Threshold Value Of Electric Field Research Articles

New features of the surface wave propagation along an exponentially graded-index layer and nonlinear substrate with generalized Kerr-type nonlinear response

New surface waves travelling along the interface between the medium with a generalization of the Kerr nonlinearity and an exponentially graded-index layer are found. The Kerr nonlinearity generalization is assumed to be an abruptly change in the values of Kerr nonlinear response parameters from one to another after the wave amplitude exceeds the threshold value of electric field. The differences between the localization features of surface waves in self-focusing and defocusing media are established. It is shown that the bulk of the surface wave energy is transferred in the optical domain formed near the interface in the case of contact between a graded-index medium and a self-focusing one, which can play the role of the core of the waveguide system. The opposite effect is observed in the case of contact between a graded-index and a defocusing medium, when the main fraction of the surface wave energy is transferred along the graded-index layer, and in the optical domain it is much lower than in a nonlinear substrate.

Analysis of Current–Voltage Characteristics in Insulating Polymers Using a Bipolar Charge Transport Model

A bipolar charge transport (BCT) model has first been used to compare the current density–voltage characteristics (J–V) for different applied voltage protocols and different times under voltage taking low-density polyethylene (LDPE) as a case study, as a steady state may take a very long time to be reached experimentally. Simulation results highlight the necessity to spend substantial time under voltage to reach a quasi-stable current. In a second part, evolutions of the model in terms of physical processes are proposed, to observe their impact on the current density–electric field (J–E) characteristics, and particularly the appearance of electric field thresholds, as proposed by the space-charge-limited current (SCLC) theory. To do so, different mathematical expressions are proposed for each physical process related to injection, mobility, and trapping. Field-dependent mobility equations allow obtaining electric field threshold values comparable to experimental data, while a constant mobility is the only way to observe a trap-free limit region. Moreover, all parameters linked to trapping are of most importance in the observation of an SCLC characteristic but are not enough to observe a trap-free limit region when the electric field-dependent mobility is considered.

Electric field driven fractal growth dynamics in polymeric medium

This paper reports the extension of earlier work (Dawar and Chandra, 2012) [27] by including the influence of low values of electric field on diffusion limited aggregation (DLA) patterns in polymer electrolyte composites. Subsequently, specified cut-off value of voltage has been determined. Below the cut-off voltage, the growth becomes direction independent (i.e., random) and gives rise to ramified DLA patterns while above the cut-off, growth is governed by diffusion, convection and migration. These three terms (i.e., diffusion, convection and migration) lead to structural transition that varies from dense branched morphology (DBM) to chain-like growth to dendritic growth, i.e., from high field region (A) to constant field region (B) to low field region (C), respectively. The paper further explores the growth under different kinds of electrode geometries (circular and square electrode geometry). A qualitative explanation for fractal growth phenomena at applied voltage based on Nernst–Planck equation has been proposed. • The paper is an extension of earlier work [Phys. Lett. A 376 (2012) 3604] on effect of electric field on DLA. • Threshold value of electric field has been determined. • Below the threshold, growth is random. • Above the threshold, the growth is governed by diffusion, migration and convection. • Different kinds of electrode geometries have been used to simulate the growth.

Electrically induced light scattering performances of lanthanum-modified lead zirconate titanate transparent ceramics

A series of lanthanum-modified lead zirconate titanate (PLZT) ceramics of Zr/Ti (70/30) with different La concentration (La = 7.6, 7.8, 8.0 mole %) were prepared by a hot pressing process. The performances of electrically induced light scattering for PLZT (X/70/30) ceramics were investigated and analyzed systematically. All samples are crystallized into a single perovskite phase. The PLZT (7.6/70/30) sample exhibits a ferroelectric behavior while both PLZT (7.8/70/30) and PLZT (8.0/70/30) samples show an antiferroelectric behavior. The phase transition temperature (Tc) of the PLZT (X/70/30) ceramics shifts slightly from ~86 °C to ~89 °C with the increasing of La concentration at 1 kHz. All three ceramic samples exhibit a high transmittance, i.e., greater than 60 %, with a thickness of 0.4 mm over a wide range of wavelength band, from visible to near IR. The PLZT (X/70/30) ceramics exhibit three different types of light scattering behavior depending on the La concentration (examined at λ = 632.8 nm). Among them, PLZT (8.0/70/30) presents a unique applicable auto-switchable property with a low threshold value of electric field and high transmittance. Noticeably, the contrast ratio increases correspondingly with the thickness of the sample, and the contrast ratio aroused by the transverse electric field is about twice as big as that aroused by the longitudinal one. The light scattering properties of the PLZT (8.0/70/30) ceramic may represent a creative application in optical modulators.

The influence of skeletal muscle anisotropy on electroporation: in vivo study and numerical modeling

The aim of this study was to theoretically and experimentally investigate electroporation of mouse tibialis cranialis and to determine the reversible electroporation threshold values needed for parallel and perpendicular orientation of the applied electric field with respect to the muscle fibers. Our study was based on local electric field calculated with three-dimensional realistic numerical models, that we built, and in vivo visualization of electroporated muscle tissue. We established that electroporation of muscle cells in tissue depends on the orientation of the applied electric field; the local electric field threshold values were determined (pulse parameters: 8 × 100 μs, 1 Hz) to be 80 V/cm and 200 V/cm for parallel and perpendicular orientation, respectively. Our results could be useful electric field parameters in the control of skeletal muscle electroporation, which can be used in treatment planning of electroporation based therapies such as gene therapy, genetic vaccination, and electrochemotherapy.

A Numerical Model of Skin Electropermeabilization Based on In Vivo Experiments

As an alternative to viral methods that are controversial because of their safety issues, chemical and physical methods have been developed to enhance gene expression in tissues. Reversible increase of the cell membrane permeability caused by the electric field--electroporation--is currently one of the most efficient and simple non-viral methods of gene transfer. We performed a series of in vivo experiments, delivering plasmids to rat skin using external plate electrodes. The experiments showed that skin layers below stratum corneum can be permeabilized in this way. In order to study the course of skin tissue permeabilization by means of electric pulses, a numerical model using the finite element method was made. The model is based on the tissue-electrode geometry and electric pulses used in our in vivo experiments. We took into account the layered structure of skin and changes of its bulk electrical properties during electroporation, as observed in the in vivo experiments. We were using tissue conductivity values found in literature and experimentally determined electric field threshold values needed for tissue permeabilization. The results obtained with the model are in good agreement with the in vivo results of gene transfection in rat skin. With the model presented we used the available data to explain the mechanism of the tissue electropermeabilization propagation beyond the initial conditions dictated by the tissue initial conductivities, thus contributing to a more in-depth understanding of this process. Such a model can be used to optimize and develop electrodes and pulse parameters.

The Course of Tissue Permeabilization Studied on a Mathematical Model of a Subcutaneous Tumor in Small Animals

One of the ways to potentiate antitumor effectiveness of chemotherapeutic drugs is by local application of short intense electric pulses. This causes an increase of the cell membrane permeability and is called electropermeabilization. In order to study the course of tissue permeabilization of a subcutaneous tumor in small animals, a mathematical model was built with the commercial program EMAS, which uses the finite element method. The model is based on the tissue specific conductivity values found in literature, experimentally determined electric field threshold values of reversible and irreversible tissue permeabilization, and conductivity changes in the tissues. The results obtained with the model were then compared to experimental results from the treatment of subcutaneous tumors in mice and a good agreement was obtained. Our results and the reversible and irreversible thresholds used coincide well with the effectiveness of the electrochemotherapy in real tumors where experiments show antitumor effectiveness for amplitudes higher than 900 V/cm ratio and pronounced antitumor effects at 1300 V/cm ratio.

Electron tunnelling from a quantum well in crossed electric and magnetic fields

The rate of electron tunnelling from a quantum well formed in a heterostructure and subjected to perpendicular dc electric and quantizing magnetic fields has been calculated. It has been shown that at a fixed value of magnetic field there exists a threshold value of electric field below which the tunnelling from the well is impossible. If the electric field exceeds the threshold value, the tunnelling rate increases with increasing electric field, but the dependence of the tunnelling rate on the electric field is not smooth because of new Landau levels being engaged, to which electrons can go over. It is exciting that the tunnelling rate in crossed electric and magnetic fields can be significantly higher than the rate in the presence of just the electric field. A physical explanation of this effect is given.

Preliminary investigation into the growth of ice crystals from the vapour in an electric field in thwe temperature range −11 to −15 °C

The growth of ice crystals from the vapour in a continuous diffusion cloud chamber is found to be profoundly influenced by the presence of an electric field. If a certain threshold value of electric field is exceeded growth becomes more rapid and needle-like crystals are formed. These crystals are seen to grow along lines of electric flux with growth velocities up to a hundred times those occuring normally. The author discusses the observed phenomena and argues that the effects occur in the vapour phase and are a consequence of the non-uniformity of the electric field created by the geometry of the growing ice crystal. The problem is shown to be explicable in terms of boundary layers at the ice/vapour interface but analytical solutions lie outside the scope of the paper.