Step Electric Field Research Articles

Hidden Real Topology and Unusual Magnetoelectric Responses in Two-Dimensional Antiferromagnets.

Recently, the real topology has been attracting widespread interest in two dimensions (2D). Here, based on first-principles calculations and theoretical analysis, the monolayer Cr2Se2O (ML-CrSeO) is revealed as the first material example of a 2D antiferromagnetic (AFM) real Chern insulator (RCI) with topologically protected corner states. Unlike previous RCIs, it is found that the real topology of the ML-CrSeO is rooted in one certain mirror subsystem of the two spin channels, and cannot be directly obtained from all the valence bands in each spin channel as commonly believed. In particular, due to antiferromagnetism, the corner modes in ML-CrSeO exhibit strong corner-contrasted spin polarization, leading to spin-corner coupling (SCC). This SCC enables a direct connection between spin space and real space. Consequently, large and switchable net magnetization can be induced in the ML-CrSeO nanodisk by electrostatic means, such as potential step and in-plane electric field, and the corresponding magnetoelectric responses behave like a sign function, distinguished from that of the conventional multiferroic materials. This work considerably broadens the candidate range of RCI materials, and opens up a new direction for topo-spintronics and 2D AFM materialsresearch.

Transient electrophoresis of a conducting cylindrical colloidal particle suspended in a Brinkman medium

The time-dependent electrophoresis of an infinitely cylindrical particle in an electrolyte solution, saturated in a charged porous medium after the sudden application of a transverse or tangential step electric field, is investigated semi-theoretically with an arbitrary double-layer thickness in an arbitrary direction relative to the cylinder. The time-dependent modified Brinkman equation with an electric force term, which governs the fluid flow field, is used to model the porous medium and is solved by using the Laplace transform technique. Explicit formulas, for the time-dependent electrophoretic velocity of the cylindrical particle in Laplace’s transform domain, have been derived for both axially and transversely when the uniform electric fields are imposed. They can also be linearly superimposed for an arbitrarily oriented relative to the electric field. Semi-analytical results for the electrophoretic velocities are presented as functions of the dimensionless elapsed time, the ratio of the particle radius to the Debye length, the particle-to-medium density ratio, and the permeability parameter of the porous medium. The results demonstrate, in general, that the growth of the electrophoretic velocities with the time scale are more slower for high permeability, and the effect of the relaxation time for unsteady electrophoresis is found to be negligible, regardless of the thickness of the double layer, the relative mass density or the permeability of the medium. The normalized transient electrophoretic velocities exhibit a consistent upward trend as the ratio of the particle radius to the Debye screening length increases. Conversely, they display a consistent downward trend as the particle-to-fluid density ratio increases, while all other parameters remain constant. The effect of the relaxation time for the transient electrophoresis is much more important for a cylindrical particle than for a spherical particle due to its smaller specific surface area.

Transient dynamic electrophoresis of a spherical colloidal particle.

A general theory is presented for the transient dynamic electrophoresis of a spherical colloidal particle in an electrolyte solution under a suddenly applied oscillating electric field. An approximate analytic expression is derived for the transient dynamic electrophoretic mobility, which is applicable for low particle zeta potentials and arbitrary Debye length. It is found that the electrophoretic mobility shows a damped oscillation, approaching its final value, unlike the case where a step electric field is applied.

Transient Electrophoresis of a Cylindrical Colloidal Particle

We develop the theory of transient electrophoresis of a weakly charged, infinitely long cylindrical colloidal particle under an application of a transverse or tangential step electric field. Transient electrophoretic mobility approaches steady electrophoretic mobility with time. We derive closed-form expressions for the transient electrophoretic mobility of a cylinder without involving numerical inverse Laplace transformations and the corresponding time-dependent transient Henry functions. The transient electrophoretic mobility of an arbitrarily oriented cylinder is also derived. It is shown that in contrast to the case of steady electrophoresis, the transient Henry function of an arbitrarily oriented cylinder at a finite time is significantly smaller than that of a sphere with the same radius and mass density as the cylinder so that a cylinder requires a much longer time to reach its steady mobility than the corresponding sphere.

Approximate Analytic Expression for the Time-Dependent Transient Electrophoretic Mobility of a Spherical Colloidal Particle.

The general expression is derived for the Laplace transform of the time-dependent transient electrophoretic mobility (with respect to time) of a spherical colloidal particle when a step electric field is applied. The transient electrophoretic mobility can be obtained by the numerical inverse Laplace transformation method. The obtained expression is applicable for arbitrary particle zeta potential and arbitrary thickness of the electrical double layer around the particle. For the low potential case, this expression gives the result obtained by Huang and Keh. On the basis of the obtained general expression for the Laplace transform of the transient electrophoretic mobility, we present an approximation method to avoid the numerical inverse Laplace transformation and derive a simple approximate analytic mobility expression for a weakly charged particle without involving numerical inverse Laplace transformations. The transient electrophoretic mobility can be obtained directly from this approximate mobility expression without recourse to the numerical inverse Laplace transformation. The results are found to be in excellent agreement with the exact numerical results obtained by Huang and Keh.

Study of the Radiation Reaction Force for a Step Electric Field and an Electromagnetic Pulse

The motions of a spin-less point-like charged particle predicted by the Landau-Lifshitz equation and the Hammond method are obtained for a step electric field, a smooth step electric field and an electromagnetic pulse by using analytical and numerical solutions. In addition to Hammond method not presenting the so-called constant force paradox, using step force brings out the apparent physical contradictions of Landau-Lifshitz equation regarding energy conservation. Nevertheless, a smooth step force shows the consistency of the Landau-Lifshitz equation. Unlike other cases, the electromagnetic pulse shows another fundamental difference between the two models. Finally, an analysis of the Hammond method is made.

A study on the mechanism of switching dynamic of ferroelectric bilayers by using Landau theory

We consider a bulk system of ferroelectric bilayer with an antiferroelectric interface coupling between two similar materials which have second-order phase transitions. Landau theory and Landau–Khalatnikov equation are used to study the dynamic switching phenomenon of this ferroelectric bilayers under a step electric field. A bilinear coupling that achieved a symmetry condition is taken into account in the Landau free-energy expression. We found that switching time is decreased for the system of weak antiferroelectric interface coupling, as well as for the system when the thickness ratio between the two layers is large. It is shown here by dynamic switching that the polarization reversal occurs in one step in the contrary to the static dielectric hysteresis loop. Negative and positive peaks of switching current is discussed.

Real-Time Electron Dynamics Study of Plasmon-Mediated Photocatalysis on an Icosahedral Al13-1 Nanocluster.

Nitrogen bond dissociation is one of the important steps in the Haber-Bosch process, where N2 is catalytically converted to NH3; however, the dissociation of the nitrogen triple bond is difficult to achieve. In this study, we investigate the possibility of nitrogen activation using plasmonic excitation of an icosahedral aluminum nanocluster. Real-time time-dependent density functional theory is employed to study the electron dynamics of the Al13-1 and [Al13N2]-1 systems. Step and trapezoidal electric fields with field strengths of 0.001 and 0.01 au and different polarization directions are applied to the systems, and the electron dynamics are analyzed. Because the occupation of nitrogen antibonding orbitals could potentially activate the N-N bond, we investigated the single-particle electronic transitions corresponding to an excitation from an occupied (O) to virtual (V) molecular orbitals (POV) of [Al13N2]-1. We found that N2 antibonding orbitals are more likely to become populated with stronger fields and also by using off-resonance fields.

Transient analysis of the nonmonotonic response of counterflow laminar diffusion flames in alternating current and step electric fields using a one-dimensional ionic transport model.

The electrohydrodynamic response of a counterflow laminar diffusion flame to applied alternating current (ac) electric fields is investigated experimentally and numerically. The flame positions are observed to show typical response to applied ac electric fields with high and moderate frequencies. The flame position does not respond above a threshold frequency corresponding to a certain collision response time, below which it oscillates in phase with the applied electric field. At a very low frequency (less than approximately 1 Hz), however, the flame position is observed to vary nonmonotonically as a function of time. To elucidate the nonmonotonic behaviors, a one-dimensional ionic transport model was employed by applying time-dependent electric fields. The responses of flame positions for ionized layers substituting for counterflow diffusion flames were systematically investigated with respect to one-way ionic wind (OIW) and two-way ionic wind (TIW) models. Consequently, it is demonstrated that the ionic models can produce not only harmonic flame oscillations for relatively low ac frequencies, but also free flame oscillations for stepwise voltages, which originated from the interaction between electrostatic force and ionic wind-induced force in the ionic system for both the OIW and TIW models.

VLF Dielectric Response and HF Localized Dielectric Discharge Measurement for Rotating Machine Insulation Assessment

This paper represents the very low frequency (VLF) dielectric response and high frequency (HF) localized dielectric discharge measurement for rotating machine insulation assessment. The integral conditions of stator winding insulation, the so-called aging condition, were investigated by the dielectric response measuring technique. The polarization and depolarization currents in the VLF range from 0.0001 to 1 Hz were measured under an external step electric field. The local conditions of stator winding insulation, the so-called weak spot condition, were examined by the partial discharge (PD) measuring technique. The PD pulse currents were detected by a capacitive sensor in a wide-band range, where the bandwidth of the measuring system was set between 30 kHz and 30 MHz. The medium voltage rotating machine rated 6.6 kV and 240 to 2,270 kW under different service conditions, i.e., new stator winding, moisture contamination, dirt contamination as well as thermally and severely aged insulation, was studied. Besides, four case studies on measuring the PD in service rotating machines rated 11–15 kV, 7100 to 211,000 kW as well as the attenuation of the PD pulses were conducted and demonstrated. With several case studies, this paper introduces new dielectric parameters, the so-called charge ratio (QR) and charge difference gradient (QDG), to identify the dielectric mechanism occurring in the stator winding insulation caused by the polarization and conduction processes. It can be concluded that the proposed parameters are a valuable tool for assessing the aging condition. In the case of the PD measurement, it was found that the PD pulse is strongly attenuated in the slot section. This paper also introduces the combination of both the dielectric response and PD measurement results, which can be very useful for assessing a complete insulation condition in the rotating machine. Moreover, the criteria for insulation conditions are suggested in this paper to evaluate the integral and local conditions for the rotating machine insulation. The local discharge in the machine causes electromagnetic waves, which may get released from the non-perfect characteristics of the enclosure. This signal may interfere with the functioning of other nearby electronic devices, especially the communication equipment. Therefore, maintaining the excellent condition of the insulation system by the proposed technique detailed in this paper will support the highly effective operational efficiency of the communication system as well.

Impact of Varied Buffer Layer Designs on Single-Event Response of 1.2-kV SiC Power MOSFETs

In this article, the single-event response of the 1.2-kV silicon-carbide (SiC) power MOSFETs with varied buffer layer designs is investigated by the 2-D numerical simulations. The structural parameters of the buffer layers are compared and analyzed to understand the transient response after the heavy ion strike and the related physical mechanisms comprehensively. Simulation results reveal that an optimized single buffer structure can be acquired by using a relatively thicker buffer layer (T $\mu \text{m}$ ) and a moderate doping concentration (D cm−3). It demonstrates that the single-event-burnout (SEB) performance can be improved significantly under the worst case bias conditions [a drain bias voltage of 1.2 kV and a linear energy transfer (LET) of 1 pC/ $\mu \text{m}$ ]. In addition, the optimized structural combinations adopted in the dual or triple buffer layers can strengthen the SEB performance further. The simulation results show that a step electric field distribution is established inside the optimized dual or triple buffers, where the electric field peak is mitigated from 3 to 2.2 MV/cm. Moreover, the excess carrier generation is suppressed and the local temperature rise is weakened during the transient electrothermal process. Consequently, the structure with the optimal buffer layer designs can enlarge the SEB safe operating area (SOA) from 30%–50% to 100% rated breakdown voltage at high LET bias, which makes the SiC power MOSFETs used in aerospace and aviation power electronic systems become possible.

Step JTE, an Edge Termination for UHV SiC Power Devices With Increased Tolerances to JTE Dose and Surface Charges

An edge termination method, referred to as guard-ring-assisted multistep junction termination extension (MS-GR-JTE), is presented for ultrahigh voltage silicon carbide (SiC) power devices. In comparisonwith other JTEs, the MS-GR-JTE creates a step electric field (EF) distribution with greatly reduced peak EF at the corners and edges of the device, resulting in a superior breakdown voltage (BV) performance with wide tolerances to JTE dose and SiC surface charges. According to the numerical simulations based on a 100- $\mu \text{m}$ -thick epilayer, an optimized MS-GR-JTE shows that the 15-kV BV performance with wide tolerances of $1.3\times 10^{12}$ cm $^{-2}$ to JTE dose and $6.1\times 10^{12}$ cm $^{-2}$ to positive surface charges are obtained, respectively, both superior to other compared JTEs.

Theoretical investigation on the performance of DNA electrophoresis under programmed step electric field strength: Two-step condition.

Programmed step electric field strength is a simple-to-use technique that has already been reported to be effective to enhance the efficiency or speed of DNA electrophoresis. However, a global understanding and the details of this technique are still vague. In this paper, we investigated the influence of programmed step electric field strength by theoretical calculation and concentrated on a basic format named as two-step electric field strength. Both subtypes of two-step electric field strength conditions were considered. The important parameters, such as peak spacing, peak width, resolution, and migration time, were calculated in theory to understand the performance of DNA electrophoresis under programmed step electric field strength. The influence of two-step electric field strength on DNA electrophoresis was clearly revealed on a diagram of resolution versus migration time. Both resolution and speed of DNA electrophoresis under two-step electric field strength conditions are simply expressed by the shape of curves in the diagram. The possible shapes of curve were explored by calculation and shown in this paper. The subtype II of two-step electric field strength brings drastic variation on the resolution. Its limitations of enhancement and deterioration of resolution were predicted in theory.

Fast high-throughput screening of H1N1 virus by parallel detection with multichannel microchip electrophoresis.

Influenza is one of the acute respiratory diseases of human caused by the influenza A (H1N1) virus and accounted for major public health concerns worldwide. The polymerase chain reaction (PCR) methods are the most popular tools for clinical diagnosis of influenza A virus. Microchip electrophoresis is a widely used method for DNA molecules separation. Herein, we describe the fast and high-throughput separation of hemagglutinin (HA) and nucleocapsid protein (NP) gene PCR products (116 bp and 195 bp, respectively) by parallel detection with multichannel microchip electrophoresis and programmed step electric field strength (PSEFS).

Fast High-throughput Screening of the H1N1 Virus by Parallel Detection with Multi-channel Microchip Electrophoresis

A multi-channel microchip electrophoresis (MCME) method with parallel laser-induced fluorescence (LIF) detection was developed for rapid screening of H1N1 virus. The hemagglutinin (HA) and nucleocapsid protein (NP) gene of H1N1 virus were amplified using polymerase chain reaction (PCR). The amplified PCR products of the H1N1 virus DNA (HA, 116 bp and NP, 195 bp) were simultaneously detected within 25 s in three parallel channels using an expanded laser beam and a charge-coupled device camera. The parallel separations were demonstrated using a sieving gel matrix of 0.3% poly(ethylene oxide) (<TEX>$M_r$</TEX> = 8,000,000) in <TEX>$1{\times}$</TEX> TBE buffer (pH 8.4) with a programmed step electric field strength (PSEFS). The method was ~20 times faster than conventional slab gel electrophoresis, without any loss of resolving power or reproducibility. The proposed MCME/PSEFS assay technique provides a simple and accurate method for fast high-throughput screening of infectious virus DNA molecules under 400 bp.

Ultra-fast separation of infectious disease-related small DNA molecules by single- and multi-channel microchip electrophoresis

An ultra-fast and precise microchip electrophoresis (ME) method was developed for the separation of infectious disease-related small DNA molecules. As a model of infectious disease-related small DNA molecules, the spike glycoprotein (S) gene of the Feline infectious peritonitis (FIP) virus was amplified using reverse transcript polymerase chain reaction. The amplified product of the FIP virus (223-bp) was analyzed within 10s by single-channel ME under a sieving gel of 0.3% poly(ethylene oxide) (Mr=8,000,000) in 1x TBE buffer (pH 8.33) and a short effective channel length of 1.3cm with a programmed step electric field strength (PSEFS) condition as follows: 470.6V/cm for 9s, 294.1V/cm 1.5s, and 470.6V/cm for 9.5s. The single-channel ME/PSEFS method was 50 times faster than that obtained with conventional slab gel electrophoresis. When the single-channel ME method was applied to a multi-channel ME for high-throughput screening, the precision of migration time and peak area showed standard deviations of less than 1.0% without any loss of resolving power. The ME assay technique provides a simple, precise and accurate method for ultra-fast analysis of infectious disease-related DNA under 400-bp.

Fast parallel detection of feline panleukopenia virus DNA by multi‐channel microchip electrophoresis with programmed step electric field strength

A multi-channel microchip electrophoresis using a programmed step electric field strength (PSEFS) method was investigated for fast parallel detection of feline panleukopenia virus (FPV) DNA. An expanded laser beam, a 10× objective lens, and a charge-coupled device camera were used to simultaneously detect the separations in three parallel channels using laser-induced fluorescence detection. The parallel separations of a 100-bp DNA ladder were demonstrated on the system using a sieving gel matrix of 0.5% poly(ethylene oxide) (M(r) = 8 000 000) in the individual channels. In addition, the PSEFS method was also applied for faster DNA separation without loss of resolving power. A DNA size marker, FPV DNA sample, and a negative control were simultaneously analyzed with single-run and one-step detection. The FPV DNA was clearly distinguished within 30 s, which was more than 100 times faster than with conventional slab gel electrophoresis. The proposed multi-channel microchip electrophoresis with PSEFS was demonstrated to be a simple and powerful diagnostic method to analyze multiple disease-related DNA fragments in parallel with high speed, throughput, and accuracy.

Influences of surface transition layer on switching time and coercive field of a ferroelectric thin film

Based on the Landau–Khalatnikov equation of motion, we first study the properties of polarization reversal in a ferroelectric thin film with surface transition layers, which can reflect a more realistic situation compared to the previous treatments of the same problem using the so-called extrapolation length. The influence of the surface transition layer on switching time and coercive field under a step electric field is discussed in detail. The results show that the surface transition layer plays a crucial role in the properties of polarization reversal in a ferroelectric thin film.

Morphology and rheology of an immiscible polymer blend subjected to a step electric fieldunder shear flow

We have investigated the structural change of an immiscible polymer blend in shear flowwhen subjected to a step electric field. During the process three-dimensional images weresuccessfully constructed with a confocal scanning laser microscope and at the same timethe transient shear stress was also measured. The interface tensor was calculated from theimages. Several factors are incorporated into the shear stress, such as the bulk viscosity, theinterfacial tension and the Maxwell stress. We performed an experiment to separate theMaxwell stress from the total shear stress. The results are discussed in terms of theinterface tensor.

Three-dimensional observation of an immiscible polymer blend subjected to a step electric field under shear flow

We have investigated the structural change of an immiscible blend consisting of two polymers with equal viscosity subjected to a step electric field under shear flow. During the process, three-dimensional images were successfully acquired with a confocal scanning laser microscope, and at the same time, the transient shear stress was also measured. From the images, the interface tensor was calculated. In a blend of polymers with equal viscosity, the total shear stress may consist of the viscous, interfacial, and electric stresses. An experiment was performed to separate these stresses, and the results are discussed in terms of the interface tensor.