Increasing Field Strength Research Articles

Reversible solid-state phase transitions in confined two-layer colloidal crystals

Using a combination of fluorescence and bright-field optical imaging, the solid-state packing structures of semi-confined two-layer spherical colloidal crystals were observed during modulation of an external AC electric field. Upon increasing field strength, the bottom layer of colloids (layer 1) transitioned from the entropically favored hexagonal packing structure with p6m symmetry to a square-packing structure with p4m symmetry. The packing structure of layer 2 was determined by the packing structure of layer 1, with layer 2 particles resting in, and moving in registry with, the low-energy interstitial sites of layer 1. Modulation of the field strength thus resulted in a reversible transition between a face-centered cubic crystal structure and a body-centered cubic crystal structure at low and high field strengths, respectively. These structures were found to be sensitive to the particle density in the wells, with vacancies and insertions leading to the formation of mixed crystal phases at high field strengths.

Charge Transfer by Polarons in a Homogeneous Poly G/Poly C-Chain Subjected to a Constant Electric Field in Terms of the Peyrard–Bishop–Holstein Model

Numerical experiments based on the Peyrard–Bishop–Holstein model have been conducted to demonstrate the possibility of charge transfer by polarons in the homogeneous Poly G/Poly C-chain of DNA subjected to a constant electric field. It has been shown that a polaron in this model can travel large distances along the chain with a constant velocity if the electric field is weak. The charge motion ceases to be uniform with an increase in field strength: the charge starts executing Bloch oscillations.

Safety of Subjects During Radiofrequency Exposure in Ultra-High-Field Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is one of the most important medical imaging techniques. Since the introduction of MRI in the mid-1980s, there has been a continuous trend toward higher static magnetic fields to obtain i.a. a higher signal-to-noise ratio. The step toward ultra-high-field (UHF) MRI at 7 Tesla and higher, however, creates several challenges regarding the homogeneity of the spin excitation RF transmit field and the RF exposure of the subject. In UHF MRI systems, the wavelength of the RF field is in the range of the diameter of the human body, which can result in inhomogeneous spin excitation and local SAR hotspots. To optimize the homogeneity in a region of interest, UHF MRI systems use parallel transmit systems with multiple transmit antennas and time-dependent modulation of the RF signal in the individual transmit channels. Furthermore, SAR increases with increasing field strength, while the SAR limits remain unchanged. Two different approaches to generate the RF transmit field in UHF systems using antenna arrays close and remote to the body are investigated in this letter. Achievable imaging performance is evaluated compared to typical clinical RF transmit systems at lower field strength. The evaluation has been performed under consideration of RF exposure based on local SAR and tissue temperature. Furthermore, results for thermal dose as an alternative RF exposure metric are presented.

Study on the electrical response of small ethanol‐air diffusion flame under the uniform electric field

Ethanol is a renewable alternative fuel in many application areas. The external electric field is applied to assist the small ethanol diffusion flame in this study. The electrical response of flame under the uniform electric field is discussed. A reduced chemical mechanism of ethanol is used to establish a numerical model corresponding to the experimental system. The characteristics of current-electric field strength, equivalent resistance, distribution of charged species, velocity field, and reaction rate are studied. The results show that the electric field brings significant effects on the combustion and electrical characteristics of flame. As the electric field strength increases, the current through the circuit and the equivalent resistance of the flame show a three-stage variation. The current increases first (0-40 kV/m), then stabilizes (40-70 kV/m) and then continues to increase (70-100 kV/m) with the increase of the electric field strength. It shows that the flame has certain electric resistance characteristic. The number density of charged species in the flame increases, and the distributions of charged species tend to move upstream by the effect of electric field. When the electric field strength is high as 100 kV/m, the charged species density increases by 10%. Meantime, the gas velocity near the flame front is accelerated and the chemical reaction rate also increases by the effect of electric field. When the electric field strength reaches 100 kV/m, the corresponding reaction rate and the corresponding flow velocity are increased by about 40% and 20%, respectively, compared with those without electric field. The calculated ionic wind velocity increases greatly with the electric field strength and shows a nearly linear increasing trend. The combined effects of the enhanced ionic wind effect, the intensified chemi-ionization process, and the increase of the concentration of charged species are considered as the main reason for the effect of electric field.

Simulation of Magnetic Electron Cut-off in a Vacuum Switch with an Anode in the Form of an Inductor

The simulation of the process of magnetic cut-off of electrons in a vacuum switch (VC) with an anode in the form of an inductor was performed. Calculations were performed according to the physico-topological model of physical processes in the vacuum switch, which took into account current distribution along electrodes, the trajectory of electrons emitted by the cathode and the conditions of current interruption in VC. Determination of current distribution along the anode, as well as configurations of electric and magnetic fields were performed according to a mathematical model based on Maxwell's equations for vacuum and conductive medium of the anode and boundary conditions adapted to the shape of the elements of the VC. Material equations were also used for certainty. The initial kinetic energy of electrons emitted from the cathode was set equal to zero. Their direction of departure from the cathode surface was determined by the direction of the lines of force of the electric field near the surface. Electron emission was given by the uniform distribution of emission points on the surface of the cathode tip. The calculation of the structure of the magnetic field was performed taking into account the secondary magnetic fields and the current distribution over the cross section of the anode inductor, which is caused by the skin effect.It is established that a decrease in the step of the inductor turns and an increase in the amplitude of the current pulse in it lead to an increase in the magnetic field strength in the cathode region, which improves the focusing of electrons. At anode-cathode voltage of 10 kV, the step of the inductor of 6 mm and the amplitude of the anode inductor current pulse of 900 A, all the electrons emitted from the cathode are focused outside the anode.The influence of design parameters on the electron cut-off efficiency is determined. For the investigated design, the optimal cathode-anode distance was 12 mm with a step between the turns of the inductor of 6 mm. The results of calculations showed that reducing the distance between the turns of the inductor increases the efficiency of electron cut-off, which confirms the physical adequacy of the mathematical model and the correctness of the calculations. Calculations also showed that at a cathode-anode distance below 12 mm, the focusing of electrons deteriorates.In the proposed design of the VC with the anode inductor in the form of three turns, the complete cut-off of electrons, i.e. the time of flight of electrons through the electrode system, at anode-cathode voltage of 10 kV, occurred by less than 1 ns at an inductor current pulse of 900 A. The inductor current pulse duration was 5 μs had the form of the half-sinusoid arc. The used method of modeling allows to establish in what part of the inductor pulse the full cut-off of electrons is provided.The obtained results can be used in the development of the VC with interruption of the current of vacuum-arc discharge.

Hygienization of mixed animal by-product using pulsed electric field in a continuous treatment system: Synergistic effect with ohmic heating on the inactivation of indicator bacteria

Thermal hygienization of waste animal by-products (ABP) before anaerobic digestion is imposed by EU regulations in order to minimize its sanitary risk during digestate land application. This process is energy and time consuming. The present paper deals with the hygienization of ABP using pulsed electric field (PEF) in a continuous system. Enterococcus faecalis ATCC 19433 and Escherichia coli ATCC 25922 were tested as indicator bacteria characterizing the microbial inactivation efficiency. Four electric field strengths (15, 20, 25 and 30 kV∙cm−1) were applied to the continuous treatment chamber where circulated the ABP suspension. Synergistic effect of PEF and ohmic heating (Tave = 41 °C) and single effect of PEF (Tave = 28 °C) on bacterial inactivation were investigated.With the effect of ohmic heating, PEF treatment at 25 and 30 kV∙cm−1 for 0.9 ms could obtain 5-log10 reduction of Ent. faecalis. This efficiency complies with the EU criteria to validate an alternative hygienization process. The time estimated by Weibull model for 5-log10 reduction of both indicator bacteria (5-D value) was significantly reduced by 2–24.5 times when the synergistic effect of PEF and ohmic heating was present. The increase in electric field strength from 25 kV∙cm−1 to 30 kV∙cm−1 did not amount to a further inactivation. PEF process coupling ohmic heating at 25 kV∙cm−1 was the most efficient for ABP hygienization among the four electric field strengths studied.

Numerical Modeling of Particles Separation Method Based on Compound Electric Field

This paper shows the results of simulation of features and usability of a proposed method for particle matter (PM) separation detection based on composite electric field. Considering the composite electric field and drag coefficient, a nonlinear dynamic model of particle separation is established. Meanwhile, the model takes into account the changes in the dynamic model caused by the different diameters and different speeds of the particles, and uses the effect of the composite electric field to separate the PM. Numerical simulation results show that the PM diameter, electric field strength, and drag force have significant effects on the separation of particles. Among them, as the drag force decreases, the particle separation displacement gradually increases, and the electric field affects the particle separation direction. In the acceleration room, the particle velocity increases with the increasing of the electric field strength. In the separation room, the displacement of the particulate matter in the Y-axis direction gradually increases from a negative displacement to a positive displacement as the electric field strength increases. The displacement forms a bow shape. When the drag coefficient is changed, the displacement will suddenly increase while it is lower than a certain value. Considering the change of electric field and drag force at the same time, the separation effect would be more obvious when the drag coefficient is smaller. The electric field strength affects the separation direction of the particulate matter.

Electromagnetic Analysis of Vertical Resistive Memory with a Sub-nm Thick Electrode.

Resistive random access memories (RRAMs) are a type of resistive memory with two metal electrodes and a semi-insulating switching material in-between. As the persistent technology node downscaling continues in transistor technologies, RRAM designers also face similar device scaling challenges in simple cross-point arrays. For this reason, a cost-effective 3D vertical RRAM (VRRAM) structure which requires a single pivotal lithography step is attracting significant attention from both the scientific community and the industry. Integrating an extremely thin plane electrode to such a structure is a difficult but necessary step to enable high memory density. In addition, experimentally verifying and modeling such devices is an important step to designing RRAM arrays with a high noise margin, low resistive-capacitive (RC) delays, and stable switching characteristics. In this work, we conducted an electromagnetic analysis on a 3D vertical RRAM with atomically thin graphene electrodes and compared it with the conventional metal electrode. Based on the experimental device measurement results, we derived a theoretical basis and models for each VRRAM design that can be further utilized in the estimation of graphene-based 3D memory at the circuit and architecture levels. We concluded that a 71% increase in electromagnetic field strength was observed in a 0.3 nm thick graphene electrode when compared to a 5 nm thick metal electrode. Such an increase in the field led to much lower energy consumption and fluctuation range during RRAM switching. Due to unique graphene properties resulting in improved programming behavior, the graphene-based VRRAM can be a strong candidate for stacked storage devices in new memory computing platforms.

Orientational ordering of point dipoles on a sphere

Arrangement of interacting particles on a sphere is historically a well known problem, however, ordering of particles with anisotropic interaction, such as the dipole-dipole interaction, has remained unexplored. We solve the orientational ordering of point dipoles on a sphere with fixed positional order with numerical minimization of interaction energy and analyze stable configurations depending on their symmetry and degree of ordering. We find that a macrovortex is a generic ground state, with various discrete rotational symmetries for different system sizes, while higher energy metastable states are similar, but less ordered. We observe orientational phase transitions and hysteresis in response to changing external field both for the fixed sphere orientation with respect the field, as well as for a freely-rotating sphere. For the case of a freely rotating sphere, we also observe changes of the symmetry axis with increasing field strength.

Coalescence, Partial Coalescence, and Noncoalescence of Two Free Droplets Suspended in Low-Viscosity Oil under a DC Electric Field.

Enhancing the electric field strength can facilitate the approach of droplets and the drainage of liquid film. However, two droplets do not coalesce but bounce off after contact under an excessively high electric field strength. To reveal the underlying mechanism, the dynamic behaviors of two free droplets suspended in low-viscosity silicone oil under a DC electric field were investigated herein. Three distinct behavior modes were successively observed by a high-speed camera with the increase in electric field strength: coalescence, partial coalescence, and noncoalescence. The mechanisms and key criteria of partial coalescence and noncoalescence were explored by studying the competition between electric force and interfacial force. The theoretical formula of critical electric field strength for droplet coalescence was derived and validated by experiments. The results indicated that the electric capillary number Ca can be used as the criterion to identify the behavior modes of two free droplets. The droplets undergo partial coalescence or noncoalescence when Ca > 0.11; otherwise, the droplets experience coalescence.

Rotating spin-1/2 Bose–Einstein condensates in a gradient magnetic field with spin–orbit coupling

We study the ground-state phases of two-dimensional rotating spin–orbit coupled spin-1/2 Bose–Einstein condensates (BECs) in a gradient magnetic field. The competition between gradient magnetic field, spin–orbit coupling and rotation leads to a variety of ground-state phase structures. In the weakly rotation regime, as the increase of gradient magnetic field strength, the BECs experiences a phase transition from the unstable phase to the single vortex-line phase. The unstable phase presents the vortex lines structures along the off-diagonal direction. With magnetic field gradient strength increasing, the number of vortex lines changes accordingly. As the magnetic field gradient strength increases further, the single vortex-line phase with a single vortex line along the diagonal direction is formed. The phase diagram shows that the boundary between the two phases is linear with the relative repulsion λ ≥ 1 and is nonlinear with λ < 1. In the relatively strong rotation regime, in addition to the unstable phase and the single vortex-line phase, the vortex-ring phase is formed for the strong magnetic field gradient and rapid rotation. The vortex-ring phase shows the giant and hidden vortex structures at the center of ring. The strong magnetic field gradient makes the number of the vortices around the ring unchanged.

Double-propagation mode in short-gap spark discharges driven by HV pulses with sub-ns rise time

The object of this study is the investigation of spark discharges ignited by unipolar positive rectangular high voltage (HV) pulses with 200 ps rise time and (15 ± 2) kV amplitude with 3 ns duration full width at half maximum in synthetic air in a 1.2 mm pin-to-pin gap (tungsten electrodes) at atmospheric pressure. The discharge development was recorded by synchronised iCCD and streak camera measurements in single-shot operation, revealing a two-stage propagation mode. The discharge started with a fast initial breakdown across the entire gap (∼10 mm ns−1) during the HV slope, followed by a much slower (∼0.1 mm ns−1) propagation originating from both electrodes towards the gap centre. The combination of high-resolution diagnostics with numerical modelling indicated that the initial breakdown phase is caused by the rapid increase of electric field strength during the steep HV slope, which leads to the simultaneous fast propagation of a positive and a negative streamer.

Effects of soil surface electric field on aggregates breakdown and water erosion in black soil region of Northeast China

Through quantitatively adjust soil electric field, we investigated the effect of soil electric field on aggregate stability and soil erosion in black soil region of Northeast China with the experiments of wet sieving and rainfall simulation. Results showed that: 1) Soil surface potential absolute value and electric field strength increased with the decreases of electrolyte concentration in bulk solution. Soil electric field strength could reach to 108 V·m-1. 2) With the increase of soil electric field strength, the degree of fragmentation of soil aggregates increased and the mean weight diameter (MWD) decreased sharply first and then kept constant. 3) With decreasing electrolyte concentration and increasing surface potential, the amount of soil loss increased. As the electrolyte concentration was &lt;0.01 mol·L-1, the corresponding soil surface potential was &gt; 210 and 209 mV for Bin-xian and Keshan, respectively, the cumulative amounts of soil loss with rainfall time almost overlapped, suggesting that the electrolyte concentration of 0.01 mol·L-1 was the threshold for soil erosion. 4) There was a linear relationship between soil cumulative loss and MWD. Our results indicated that soil electric field strength increased as the rain enters into the soil, which could induce soil aggregate breakdown and release amounts of fine soil particles. Finally, soil erosion occurred under the driving of flowing water. Our results provided insights into the mechanism underlying soil erosion in the black soil region of Northeast China.

Influence of (Er3+, La3+, Ce4+) additions on physical and optical properties of 50CaO–50P2O5 glasses

Calcium phosphate glass samples with the addition of 5 mol% of three different rare earth oxides (Erbium, Lanthanum and Cerium oxides) were made by melt quenching process. Effect of rare earth ions addition on structural, physical and optical properties has been investigated using density measurement, XRD diffraction, Fourier transformed infrared (FTIR) spectroscopy, ultra violet visible spectroscopy and Abbe Refractometer. The random short range order of synthesized glass samples was analyzed by XRD diffraction. The absorption spectra have been recorded and optical band gap energy was determined by using Tauc plotting. The band gap energy showed a decrease when 5 mol% of rare earth (Er2O3, La2O3, and CeO2) oxides were added to the host glass. Fourier transformed infrared (FTIR) spectrometer was applied to study the structural changes of the synthesized glasses. The density and refractive index of synthesized glasses was measured and related parameters were calculated. These values are compared with the un-doped metaphosphate glass. Based on measured density, the concentrations of added rare-earth ion is calculated. With an increase in ion concentration, the internuclear distance decreased leading to an increase in field strength.

Efficiency and cell viability implications using tip type electroporation in zebrafish sperm cells.

Sperm-mediated gene transfer (SMGT) has a potential use for zebrafish transgenesis. However, transfection into fish sperm cells still needs to be improved. The objective was to demonstrate the feasibility of tip type electroporation in zebrafish sperm, showing a protocol that provide high transfection efficiency, with minimal side-effects. Sperm was transfected with a Cy3-labelled DNA using tip type electroporation with voltages ranging from 500 to 1500 V. Sperm kinetics parameters were assessed using Computer Assisted Semen Analysis (CASA) and cell integrity, reactive oxygen species (ROS), mitochondrial functionality and transfection rate were evaluated by flow cytometry. The transfection rates were positively affected by tip type electroporation, reaching 64.9% ± 3.6 in the lowest voltage used (500 V) and 86.6% ± 1.9 in the highest (1500 V). The percentage of overall motile sperm in the electrotransfected samples was found to decrease with increasing field strength (P < 0.05). Increase in the sperm damaged plasma membrane was observed with increasing field strength (P < 0.05). ROS and sperm mitochondrial functionality did not present a negative response after the electroporation (P > 0.05). Overall results indicate that tip type electroporation enhances the internalization of exogenous DNA into zebrafish sperm cells with minimal harmful effects to sperm cells.Electronic supplementary materialThe online version of this article (10.1007/s11033-020-05658-2) contains supplementary material, which is available to authorized users.

Competitive Electrohydrodynamic and Electrosolutal Advection Arrests Evaporation Kinetics of Droplets.

This article reports the hitherto unreported phenomenon of arrested evaporation dynamics in pendant droplets because of electric field stimulus. The evaporation kinetics of pendant droplets of electrically conducting saline solutions in the presence of a transverse, alternating electric field is investigated experimentally. While the increase of field strength reduces the evaporation rate, increment in field frequency has the opposite effect. The same has been explained on the solvation kinetics of ions in polar water. Theoretical analysis reveals that change in surface tension and the diffusion-driven evaporation model cannot predict the decelerated evaporation. With the aid of particle image velocimetry, suppression of internal circulation velocity within the droplet is observed under electric field stimulus, which directly affects the evaporation rate. A mathematical scaling model is proposed to quantify the effects of electrohydrodynamic circulation and electrothermal and electrosolutal advection on the evaporation kinetics. The analysis encompasses major governing parameters, namely, the thermal and solutal Marangoni numbers, the electrohydrodynamic number, the electro-Prandtl and electro-Schmidt numbers, and their respective contributions. It has been shown that the electrothermal Marangoni effect is suppressed by the electric field, leading to deteriorated evaporation rates. Additionally, the electrosolutal Marangoni effect further suppresses the internal advection, further reducing the evaporation rate by a larger proportion. Stability analysis reveals that the electric body force retards the stable internal advection. The stability mapping also illustrates that if the field strength is high enough for the electrosolutal advection to overshadow the solutal Marangoni effect completely, it can lead to improvement in evaporation rates.

Effects of static magnetic field on Chlorella vulgaris: growth and extracellular polysaccharide (EPS) production

In this study, Chlorella vulgaris treated with static magnetic field (SMF) was investigated in terms of the algal density, biomass, extracellular polysaccharide content and distribution, percentage of algal aggregation, total protein content, enzyme activity, malondialdehyde content, and nutrient removal. The algal density and biomass under 800 G SMF were highest on the 16th day and were 29.02% and 35.67% greater than the control group (0 G group), respectively. Soluble EPS decreased with an increase in magnetic field strength, while bound EPS exhibited an opposite trend. Algal aggregation occurred in all treatment groups, with the aggregation percentage in the high magnetic field-treated groups being lower than that in the control group. Total protein content of the 800 G group was the lowest at 1.13 μg (106 cells)-1 and the enzyme activity of treated algae was higher than that of the control group. SMF affected the growth and reproduction of C. vulgaris by affecting the antioxidant response.

Initial Results From the Newly Upgraded LTX-β

LTX-β, the upgraded Lithium Tokamak Experiment, recently began its first campaign with a goal to study the transport properties of gradient-free electron temperature profile equilibria with increased toroidal field and neutral beam injection. The temperature-gradient-free equilibria in LTX were enabled by the lithium plasma-facing surface. To make the lithium surface conditions more consistent for LTX-β, a new, faster lithium evaporator system has been developed. The toroidal magnetic field has been nearly doubled to ≥0.3 T. Auxiliary heating and fueling with a high flux (35 A, 20 kV) neutral beam has begun. The beam provides core fueling without cold edge neutrals, to test whether flat temperature profiles can be sustained, and makes possible core ion temperature measurements via charge exchange recombination spectroscopy. Neutral beam fueling has been demonstrated with increases in line-integrated density. The coupling of the beam matches well with NUBEAM predictions for shine through. Improved performance has been observed following lithium evaporative coatings and an increase in field strength.

Experimental Observation and Numerical Analysis of the Arc Plasma Axial Motion in a Magnetically Rotating Arc Plasma Generator

To better understand the arc plasma axial motion under an axial magnetic field, a high-speed charge-coupled device camera was used to observe the arc plasma images in a magnetically rotating arc plasma generator. Experimental results indicate that the arc plasma moves towards the cathode bottom as the magnetic field strength increases, while a higher arc current facilitates the cathode arc root to move to the cathode terminus. A two-dimensional coupled model was used to analyze the arc plasma axial motion under different magnetic field strengths. The numerical simulation shows that the arc plasma is axially compressed and curves towards the cathode bottom. It is proposed that the arc plasma structure is derived from the strong backflow from the anode outlet, which is induced by the low-pressure region near the cathode. Moreover, the coupled model predicts the movement of the cathode arc root in agreement with the experimental results. It is inferred that the movement of the cathode arc root is relevant to the energy flux, which is transported from the arc column plasma to the cathode surface.

Estimating surface electric fields using reactive formic acid probes and SEM image brightness analysis

By changing the electrical bias imposed on a Ni catalyst attached to an external circuit, the selectivity of catalytic formic acid decomposition is shown to change—favoring CO2/H2 production under negative bias and CO/H2O production under positive bias. A method for estimating the strength of externally generated surface electric fields by measuring this selectivity change is presented and used to approximate field strengths on the order of 0.20 V/nm. A COMSOL model of the catalyst was created which indicated that the presence of Ni particles increased field strength and uniformity across the catalyst. Comparing this model to SEM imaging of the catalyst verified that the field strengths are highest on the surface of the catalyst particles, pore edges, and microscopic defects. The methods developed herein may be useful to future reaction engineers seeking to incorporate applied electric fields into process designs.