Direct Current Field Research Articles

Importance of an Axial LnIII-F Bond across the Lanthanide Series and Single-Molecule Magnet Behavior in the Ce and Nd Analogues.

The recently reported compound [DyIIILF](CF3SO3)2·H2O (L = 1,4,7,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraaza-cyclododecane) displays a strong axial magnetic anisotropy, due to the short axial Dy–F bond, and single-molecule magnet (SMM) behavior. Following our earlier [DyIIILF]2+ work, herein we report the systematic structural and magnetic study of a family of [LnIIILF](CF3SO3)2·H2O compounds (Ln(III) = 1-Ce, 2-Pr, 3-Nd, 4-Eu, 5-Tb, 6-Ho, 7-Er, 8-Tm, and 9-Yb). From this series, the Ce(III) and Nd(III) analogues show slow relaxation of the magnetization under an applied direct current magnetic field, which is modeled using a Raman process. Complete active space self-consistent field theoretical calculations are employed to understand the relaxation pathways in 1-Ce and 3-Nd and also reveal a large tunnel splitting for 5-Tb. Additional computational studies on model compounds where we remove the axial F– ligand, or replace F– with I–, highlight the importance of the F– ligand in creating a strong axial crystal field for 1-Ce and 3-Nd and for promoting the SMM behavior. Importantly, this systematic study provides insight into the magnetic properties of these lighter lanthanide ions.

Obtaining high dielectric constant and breakdown strength in composites with asymmetric MXene filler and highly insulative PVC matrix

Utilizing percolation of symmetric MXene filler easily achieves high dielectric constant in polymer/MXene composites. However, percolation leads to low breakdown strength. In present work, we have adopted a new strategy of employing asymmetric bimetallic VTiC MXene filler to fabricate composite dielectrics with highly insulating polyvinyl chloride (PVC) matrix. VTiC filler was prepared via heat-pressing and etching. PVC/VTiC composite films with varied filler contents were prepared via solution cast. Different surface work functions of VTiC were confirmed via density functional theory (DFT) calculations. Compared with several polymer/symmetric monometallic MXene composites in our prior works, PVC/VTiC composites show simultaneously improved dielectric and breakdown properties. In later, high dielectric constant stems from cooperation of filler's asymmetry and polymer/filler interface polarization, and high breakdown strength is rooted in matrix's ultrahigh insulation. Optimized PVC/VTiC composite with 10 wt% filler possesses a high dielectric constant of ∼203, low dielectric loss of ∼0.13 at 100 Hz and high breakdown strength of ∼374 MV m−1 at direct-current field. Innovation of this work is use of asymmetric MXene filler for constructing polymer-based composite dielectrics with promising properties. This work might pave a road for large-scale preparation of advanced dielectrics for capacitors.

Nonlinear Hall response in the driving dynamics of ultracold atoms in optical lattices

We propose that a nonlinear Hall response can be observed in Bloch oscillations of ultracold atoms in optical lattices under the condition of preserved time-reversal symmetry. In the short-time limit of Bloch oscillations driven by a direct current (dc) field, the nonlinear Hall current dominates, being a second-order response to the external field strength. The associated Berry curvature dipole, which is a second-order nonlinear coefficient of the driving field, can be obtained from the oscillation of atoms. In an alternating current (ac) driving field, the nonlinear Hall response has a double frequency of the driving force in the case of time-reversal symmetry.

Effects of electric field on microstructure evolution and defect formation in flash-sintered TiO2

Various ceramic materials have been successfully flash sintered via mostly direct current (DC) and some by alternative current (AC). However, a direct comparison on the effects of different field types on the overall microstructure and atomistic defect distribution in flash-sintered ceramics is still very limited. In this work, rutile TiO2 was chosen as a model system to directly compare the effects of DC and AC fields on microstructure and defect distribution. DC flash-sintered TiO2 presents asymmetrical distributions of grain sizes and defects, while AC sintered TiO2 have more homogeneous microstructures. More interestingly, we demonstrated a reverse-polarity flash sintering technique can achieve dense TiO2 bulk samples with homogeneous microstructure and tunable defect gradient, which are previously not attainable from either DC or AC sintering alone. This study shows the importance of field on the microstructures of flash-sintered ceramics and the great potential in achieving dense and uniform microstructures via effective field control process.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Functionalization of Keggin Fe13-Oxo Clusters.

Two Keggin Fe13-oxo clusters, [Pr12Fe33(NO3)6(L-van)4(D-van)5(TEOA)12(μ3-OH)12(μ4-OH)12(μ4-O)28(H2O)4]·(ClO4)3·(NO3)·10H2O (1) and [Dy12Fe33(NO3)2(L-van)3(D-van)3(TEOA)12(μ3-OH)18(μ4-OH)6(μ4-O)28(H2O)9]·(ClO4)5·(NO3)6·15H2O (2), where L-van = l-valine, D-van = d-valine, and TEOA = triethanolamine, were prepared by using Ln3+ as a stabilizer. Cluster 1 crystallizes in a chiral space group of C2, while cluster 2 crystallizes in a centrosymmetric space group of Pnma. Dynamic magnetic measurements of 2 under a zero direct-current field reveal that 2 exhibits single-molecule-magnet characteristics with an energy barrier of 18.79 K. Significantly, the formation of the chiral cluster 1 is closely related to the larger radius of the Pr3+ ion.

Nanoparticle-modified coatings by electrophoretic deposition for corrosion protection of magnesium

ABSTRACT Magnesium (Mg) and its biocompatible alloys are used as biodegradable materials for temporary implant applications. However, the fast electrochemical reactions in the physiological environment can lead to premature implant failure and damage the surrounding tissues. Here, we report on nanoparticle-modified biopolymer composite coatings processed using alternating current electrophoretic deposition (AC-EPD) to control the corrosion process of Mg–Al alloys. Chitosan–gelatin coatings incorporating bioactive glass particles as reinforcement were supplemented with ZnO and CeO2 nanoparticles and the corrosion resistance was evaluated. CeO2 nanoparticle-modified coatings obtained using AC signals superimposed with a direct current field appeared compact and homogeneous. ZnO nanoparticle-modified coatings had a low surface coverage with significant defects. As a result, CeO2-supplemented coatings processed for as little as 4 min effectively reduced the corrosion current density (i corr) of Mg–Al in Ringer’s solution, whereas ZnO-supplemented coatings did not. CeO2 nanoparticle-modified biopolymer coatings hold potential for fine-tuning the degradation of Mg implants.

Open magnetic shielding for static and alternating field.

To meet the increasing and various demands for low magnetic field measurement, an open magnetic shielding system created using a combination of copper coils and precisely designed superconducting closed coils is proposed. After testing, the prototype system showed a shielding factor of more than 10 000 in the direct current field and most importantly, a shielding factor of at least 100 in the alternating field from frequencies of 0.01-100Hz in a 5cm spherical volume. We interestingly found that the magnetic purity of the open system is capable of catching up with the magnetically shielded room with moderate performance. The structure and principle of the system are introduced in this paper. A key factor that makes the system possible is the decoupled interaction between the copper coils and superconducting coils. The limitations of this system and ways to improve its performance are discussed. This novel approach provides a more sophisticated and flexible way to achieve open magnetic shielding.

Current Density Limit of DC Grounding Facilities Considering Impact on Zebrafish (Brachydanio rerio)

Grounding facilities, including high-voltage DC grounding electrodes and auxiliary anodes in impressed current cathodic protection systems, inject current into the ground. This study developed an experimental platform to determine the safe limit of current density for such facilities through an analysis of fish behavior on the platform. Zebrafish (Brachydanio rerio) were selected for the experiment and placed in a tank; two rod electrodes were used to inject direct current into the water. A wireless camera was focused on the water tank to video record possible changes in fish behavior. The output voltage of the DC power source was varied, and the trajectories of the fish under various direct current fields were recorded. A tracking program was developed to analyze the trajectories and quantify the behavior of the fish. A new method combining the trajectories of fish samples with the results of current density calculations for analysis was proposed. Results demonstrated that the zebrafish could sense current in the water and turn when exposed to certain current densities. The intensity of the current at the turning points was statistically analyzed, and the threshold of current density at which the fish could no longer tolerate the current and turned was 0.4231 A/m2.

Analysis of Red Blood Cell Movement in Whole Blood Exposed to DC and ELF Electric Fields.

To evaluate hematological effects of direct current (DC) and alternating current (AC) extremely low frequency (ELF) electric field exposure, this study investigated red blood cell (RBC) movement in whole blood. Video images of RBCs were recorded under a microscope using specially designed electrode systems. Video analysis software was then used to measure the RBC velocity. The noise level and measurement system stability were confirmed based on results of a no‐field exposure experiment. Using the electrode system to produce a non‐homogeneous electric field, different movements were found to occur in DC and AC field exposure. The RBCs moved in the directions of the electric field and the gradient of field distribution, respectively, in the DC and AC fields. Dependences of the RBC velocity on the field strength were, respectively, linear and quadratic in the DC and AC fields. These results suggest that electrophoretic and dielectrophoretic movements were, respectively, dominant in the DC and AC fields. The magnitude of the electric field necessary to cause these effects was found to be 103–105 times greater than the internationally publicized guideline for human safety. © 2022 Bioelectromagnetics Society.

Effect of Magnetohydrodynamic on Cutaneous Wound Healing in Rat Model

Background: Exogenous electrical stimulation of the skin may mimic its endogenous bioelectric currents. In this study, a combination of direct current (DC) and magnetic field (MF) was investigated in an excision wound model in rats. Methods: A circular wound was created on the posterior of the neck, and an electrode was fixed in the wound center. Rats were divided into sham, DC (600 µA), MF (~0.8 T), and magnet-direct current (MDC) groups. The study was conducted in 14 days with 20-min treatment daily. Results: The DC and MDC groups had higher healing percentages (P < 0.01) with mean differences of -13.42 and -15.63, respectively. Direct current on days 2, 5, and 6, and MDC on days 8, 9, 10, 11, 12, and 13 showed higher wound closing. In the DC-treated group, angiogenesis was improved on day 7. In MDC-treated rats, angiogenesis and fibroplasia were improved on day 13. The MF and MDC groups had lower granulation thicknesses on day 7. Granulation thickness increased on day 13 in the MF and MDC groups, while it decreased in the DC group. Direct current treatment improved healing in the first half of the study period, whereas MDC enhanced it in the second half, overtaking DC. From day 7, the magnet group's healing started to overtake the control group slightly in the last four days. Conclusions: To accelerate wound healing, we suggest applying DC in the first days of wounding and MDC in the following days.

The influence of the processing parameters on the reactive flash sintering of ZrO2‐CeO2

AbstractReactive flash sintering (RFS) is a method that was recently developed to produce dense single‐phase bulk ceramic parts through solid‐state reactions in a single‐step that only takes a few minutes. The influence of the RFS parameters on the phase purity of a simple mixed oxide, (Zr0.8,Ce0.2)O2, was investigated. Parameters such as furnace temperature, furnace atmosphere, electric current density, and alternating current (AC) or direct current (DC) were examined. It was found that (Zr0.8,Ce0.2)O2 pellets with high densities, above 90% of its theoretical density, can be produced by RFS in a few minutes when RFS occurs under oxidizing atmospheres, AC fields with current densities of 100 mA·mm−2, and at a furnace temperature of 1200°C. Reducing conditions such as Ar‐H2 atmosphere and DC fields, low furnace temperatures, and low current densities resulted in phase impurities and poor reactions between the ZrO2 and the CeO2 powders. These results show that RFS is a useful method to produce mixed oxides, but it is very sensitive to the processing parameters. This is the first time that the influence of most of the RFS processing parameters has been studied systematically. Thus, the present work aims to provide guidelines on selecting the right processing parameters when exploring RFS.

Achieving a high dielectric constant and low dielectric loss of polymer composites filled with an interface-bonded g-C3N4@PbS narrow-bandgap semiconductor

Scattering medium-bandgap semiconductors into polymers cannot remarkably improve the dielectric constant in composites. Nanoscale ceramic leads to a high interface leakage current. To obtain a high dielectric constant and low loss, in this work, graphitic carbon nitride (g-C3N4)@PbS microparticles were prepared for fabricating polymer-based ternary composites. Polymer/PbS binary composites were also fabricated. In terms of electric properties, ternary composites show more advantages than binary composites. In ternary composites, the improved dielectric constant is ascribed to SN bonding at the g-C3N4/PbS interface. Decreased dielectric loss is rooted in the reduced interface leakage current (from the large size of the hybrid filler) between the polymer and PbS. Under high fields, the reduced breakdown strength is attributed to the reduced bandgap in the hybrid filler compared with PbS and g-C3N4. The innovation of this work is the high-efficiency collaboration between microsized and interfacial SN bonding in g-C3N4@PbS filler. The ternary composite with 15 wt% hybrid filler has a high dielectric constant of ~ 39 and a low dielectric loss of ~ 0.04 at 100 Hz (low field) as well as a high breakdown strength of ~ 202 MV m−1 under a direct-current field. This work might enlighten the fabrication of polymer composites with great promise in energy storage.

Design and Optimization of a BAW Magnetic Sensor Based on Magnetoelectric Coupling.

Magnetic sensors actuated by bulk acoustic wave (BAW) have attracted extensive attention due to the fact of their high sensitivity, GHz-level high frequency, and small size. Different from previous studies, suppression of energy loss and improvement in energy conversion efficiency of the BAW magnetoelectric (ME) sensor were systematically considered during the device design in this work. Finite element analysis models of material (magnetic composite), structure (ME heterostructure), and device (BAW ME magnetic sensor) were established and analyzed in COMSOL software. Additionally, the magnetic composite was prepared by radio frequency magnetron sputtering, and its soft magnetism was characterized by magnetic hysteresis loop and surface roughness. The research results demonstrate that after inserting four layers of 5 nm Al2O3 films, a performance of 86.7% eddy current loss suppression rate, a less than 1.1% magnetostriction degradation rate, and better soft magnetism were achieved in 600 nm FeGaB. Furthermore, compared with other structures, the two-layer piezomagnetic/piezoelectric heterostructure had a better ME coupling performance. Eventually, the design of the BAW ME magnetic sensor was optimized by the resonance-enhanced ME coupling to match the resonance frequency between the magnetic composite and the BAW resonator. When a 54,500 A/m direct current bias magnetic field was applied, the sensor worked at the first-order resonance frequency and showed good performance. Its linearity was better than 1.30%, the sensitivity was as high as 2.33 μmV/A, and the measurement range covered 0–5000 A/m.

Study on two anammox start-up and operation strategies: Low-intensity direct current electric field and negative pressure

The bottlenecks of applying the anaerobic ammonia oxidation (Anammox) process are the low growth rate of anaerobic ammonium oxidation bacteria (AnAOB) and the sensitive response to the environment. How to rapidly enrich AnAOB is of great significance for its future application. This study focused on the effects of low-intensity direct current field (DCF) and negative pressure (NP) operating systems on granulation process, extracellular polymeric substance (EPS) secretion, AnAOB activity, and microbial community structure of granules. The results showed that appropriate DCF stimulation could accelerate the growth rate of AnAOB and promote more EPS secretion. Nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) of total nitrogen (TN) reached the highest under 2 V voltage intensity. NP could accelerate the reaction rate of the system and enhance the sludge retention capacity of the reactor. The two start-up strategies can shorten 30–33% anammox start-up time and maintain 86–88% NRE. These results indicate that the two start-up strategies have feasibility and potential for the rapid start-up and stable operation of the Anammox process.

Electric field simulations of field grading techniques in HVDC cable joints

PurposeIn high voltage direct current cable systems, cable joints are known as the least reliable components due to the use of multiple dielectrics. Resulting from the electric field and temperature depending conductivity of the different dielectrics, field enhancement at critical areas, e.g. triple points, may result in accelerated aging and the failure of the component. To reduce the stress, different field grading techniques are applied. The purpose of this study is to investigate different grading techniques for cable joints. Different shapes of the electrode and a varying nonlinear conductivity of field grading materials (FGM) are used for the simulation of the electric field.Design/methodology/approachCoupled electro-thermal field simulations are applied for different joint geometries, to obtain the stationary electric field. Electric field simulations in cable joint using geometric and nonlinear field grading techniques are shown.FindingsUsing the geometric field grading, the shape of the stress cone determines the field values in critical areas (triple points). High stress reduction is obtained for a certain curvature of the stress cone. For the nonlinear stress control, materials with a higher conductivity in comparison to the cable and the joint material are used. A field reduction is obtained by increasing the total conductivity. On the other hand, this is also increasing the insulation losses within the total FGM. More applicable is the decrease of the switching field or the increase of nonlinearity, which is only locally increase the conductivity and the insulation losses. Furthermore, simulations results show that an approximately constant field reduction is obtained, if the nonlinearity is above a certain threshold.Research limitations/implicationsThis study is restricted to a field dependency of FGM only. For impulse voltages, high temperature and electric conductivity values my result in a thermal runaway. Furthermore, only direct current field grading techniques are studied.Originality/valueThe field grading of cable joints, using geometric and nonlinear techniques, is analyzed. A comparison between the electric field, by varying the curvature of the ground stress cone or the FGM conductivity constants in a complex joint geometry is novel. With its effect on the electric fields, general requirements for the geometry (geometric field grading) or the values of the FGM constants (nonlinear field grading) are defined to obtain a sufficient field grading.

Dispersion of single-walled carbon nanotubes in water in presence of Direct Current field

Dispersion of single-walled carbon nanotubes in water in presence of Direct Current field

Insights into the behavioural responses of juvenile thornback ray Raja clavata to alternating and direct current magnetic fields.

As part of energy transition, marine renewable energy devices (MRED) are currently expanding in developed countries inducing the deployment of dense networks of submarine power cables. Concern has thus raised about the cable magnetic emissions (direct or alternating current) because of potential interference with the sensorial environment of magneto-sensitive species, such as sharks and rays. This study sought to assess the short-term behavioural responses of juvenile thornback rays (Raja clavata) (n = 15) to direct and alternating (50 Hz) uniform 450-μT artificial magnetic fields using 1 h focal-sampling design based on a detailed ethogram. Careful control of magnetic fields' temporal and spatial scales was obtained in laboratory conditions through a custom-made Helmholtz coil device. Overall, qualitative or quantitative behavioural responses of juvenile rays did not significantly vary between control vs. exposed individuals over the morning period. Nonetheless, rays under direct current magnetic field increased their activity over the midday period. Synchronisation patterns were also observed for individuals receiving alternating current exposure(chronologic and qualitative similarities)coupled with a high inter-individual variance. Further studies should consider larger batches of juveniles to address the effect of long-term exposure and explore the sensitivity range of rays with dose-response designs.

DC electric field-driven heartbeat phenomenon of gallium-based liquid metal on a floating electrode.

The heart beating phenomenon of room temperature liquid metal (LM) mercury has attracted much attention in the past years, but its research and application are limited because of the low vapor pressure and high toxicity. Here, a fundamental scientific finding is reported that the non-toxic eutectic gallium indium (EGaIn) alloy droplets beat periodically at a certain frequency based on a floating electrode under the stimulation of the direct current (DC) field. The essential characteristics of heart beating are the displacement and the projected area change of the LM droplet. The mechanism of this phenomenon is the self-regulation of interfacial tension caused by chemical oxidation, chemical corrosion, and continuous electrowetting. In this article, a series of experiments are also carried out to examine the effects of different factors on the heartbeat, such as voltage, the volume of the droplet, the droplet immersion depth, the electrolyte solution concentration, the distance of electrodes, and the type of floating electrode. Finally, the heartbeat state and application boundary of the LM droplet under different conditions are summarized by imitating the human life process. The periodic changes of the LM droplet under an external DC electric field provide a new method to simulate the beating of the heart artificially, and can be applied to the research of organ chip fluid pumping in the future.

Bone Tumor Suppression in Rabbits by Hyperthermia below the Clinical Safety Limit Using Aligned Magnetic Bone Cement (Small 3/2022)

Bone Tumor Suppression Magnetic bone cement incorporating magnetically soft zinc ferrite nanoparticles and aligned in a direct current magnetic field realized exceptionally high heating power in live animals under clinically safe field parameters for hyperthermia. Suppression of osteosarcoma in rabbits by hyperthermia substantially enhances survival rate. More details can be found in article number 2104626 by Shuli He, Qinggang Ge, Yang Lv, Hao Zeng, and co-workers.