Unipolar Current Research Articles

Current–voltage characteristics of Ag/Nb:SrTiO3/Ag and Au/Nb:SrTiO3/Ag heterostructures

Ag/Nb:SrTiO3(NSTO)/Ag and Au/NSTO/Ag structures were prepared and their current–voltage curves were studied in detail. The Ag/NSTO/Ag structure can demonstrate a pronounced resistive switching effect and the characteristics of its resistance change sequence as demonstrated in the I–V curves are significantly different from those of the Au/NSTO/Ag structure. Under a unipolar current, the Ag/NSTO/Ag structure translates first from a low-resistance state (LRS) to a high-resistance state (HRS) and then from the HRS to the LRS. However, the Au/NSTO/Ag structure only shows a transition from the HRS to the LRS. The phenomenon is analyzed taking into account the migration of oxygen ions and the electrochemical reaction of the Ag electrode, which lead to the formation of the Ag2O insulation layer as well as Ag conductive filaments in the Ag/NSTO/Ag structure and a change in the barrier height of the Au/NSTO interface.

Exploring GVS as a display modality: signal amplitude and polarity, in various environments, impacts on posture, and with dual-tasking.

Galvanic Vestibular Stimulation (GVS) has been proposed as an alternative display modality to relay information without increasing demands on the visual or auditory sensory modalities of the wearer or in environments where those modalities cannot be used (e.g., covert night operations). We further investigated this concept with four experiments designed to test: (1) thresholds at which subjects could distinguish between different GVS current amplitudes and polarities, (2) thresholds at which different bipolar (i.e., sinusoidal waveform with current oscillating between left and right directions) current frequencies were distinguishable among room temperature, hot, cold, and windy environments, (3) effects of unipolar (i.e., sinusoidal waveform with current occurring in only the left or right direction) currents on balance performance, and (4) dual-task performance among frequency and polarity modulated GVS conditions during a concordant visual search task. Subjects reliably distinguished between current amplitudes that varied from a pedestal of ± 0.6mA by a median of 0.03mA (range of 0.02-0.32mA) and between unipolar currents at a median amplitude of 0.55mA (range of 0.32-0.83mA). GVS frequency thresholds were robust to the environment conditions tested, with no statistical differences found. Sway and balance errors were increased with unipolar currents. GVS thresholds were not impacted by the dual-task paradigm, but the visual search scores were slightly elevated when congruently performing a polarity thresholding task. Overall findings continue to support GVS use as a display modality, but some limitations are noted, such as the use of unipolar currents under scenarios where postural control is important.

Examination of Non-Sinusoidal Current Drive in Direct Current excited Reluctance Motor

A Direct Current excited Reluctance Motor (DCRM) powered by three-phase sinusoidal currents is expected to have a higher torque density than a Switched Reluctance Motor (SRM) powered by unipolar currents because they can achieve a greater angular variation of magnetic co-energy even in the magnetic saturation region. In this study, a non-sinusoidal current drive method for DCRM is proposed to increase torque. The non-sinusoidal current waveform is defined by a Fourier series function, and the optimum coefficients of the current function are solved using nonlinear programming. According to simulation results, the average torque of a DCRM driven by optimized non-sinusoidal current waveform is increased. Furthermore, the current balance between the armature coil and the excitation coil is investigated. As a result, the average torque is increased by up to about 25% when compared to conventinal sinusoidal current drive.

Charging Effects in Inlet Capillaries.

Glass or metal inlet capillaries are commonly used for flow restriction in atmospheric pressure ionization mass spectrometers. They exhibit a high ion transmission rate and stability at most operating conditions. However, transferring unipolar currents of ions through inlet capillaries can lead to sudden signal dropouts or drifts of the signal intensity, particularly when materials of different conductivity are in contact with the capillary duct. Molecular layers of water and other gases such as liquid chromatography solvents always form on the surfaces of inlet capillaries at atmospheric pressure ionization conditions. These surface layers play a major role in ion transmission and the occurrence of charging effects, as ions adsorb on the capillary walls as well, charging the walls to electric potentials of up to kilovolts and eventually leading to a hindrance of ion transport into or through the capillary duct. In this work, surface charging effects are reported in dependence on the capillary material, i.e., borosilicate glass, (reduced) lead silicate, quartz, and metal. Low electrical conductance materials show a more pronounced long-term signal drift (e.g., quartz), while higher electrical conductance materials lead to stable long-term behavior.

Numerical methodology to evaluate unipolar saturation current limit of DC corona discharge in complex geometries

The unipolar saturation current limit ({I}_{sat}) gives an upper limit to the corona current that can be obtained from a unipolar corona discharge. Therefore, it implies a theoretical limit to the performance of unipolar corona discharge devices. However, it has not been widely used in practice because it is difficult to deal with complex discharge configurations in an analytical way. This study aims to establish and validate a numerical methodology to evaluate the maximum current, which numerically imitates the unipolar saturation current limit. It was shown that the maximum current has the same mathematical definition as the unipolar saturation current. For validation, the maximum current was compared with an analytical solution of the Poisson equation for the coaxial cylinders configuration. The differences between the maximum current and unipolar saturation current limit for the coaxial cylinders, pin-to-plane, and single wire-to-plane configurations were discussed in terms of the assumptions used in the semi-analytical derivation of the unipolar saturation current limit. The validated methodology was applied to a multiple wire-to-plane configuration, for which a semi-analytical expression of the unipolar saturation current limit has not yet been developed. The effects of geometric and operation parameters on the maximum currents of the multiple wire-to-plane configuration were analyzed. The results were regressed into a single formula.

ФОРМУВАННЯ БІПОЛЯРНИХ ІМПУЛЬСНИХ СТРУМІВ У НАВАНТАЖЕННІ ЄМНІСНИХ НАКОПИЧУВАЧІВ ЕНЕРГІЇ ЕЛЕКТРОРОЗРЯДНИХ УСТАНОВОК

A method is proposed for stabilizing the transient discharge processes of capacitive energy storages (CESs) of electric discharge installations (EDIs) to a load whose electrical resistance can vary non-linearly and stochastically. The method is based on the use of one direct voltage generator (DVG) in the EDI, which carries out alternately an oscillatory charge of two CESs to the required voltage, as well as on the introduction of semiconductor switches into the charge circuit and discharge one of these CESs and the developed algorithms for switching them on, according to which bipolar discharge currents are formed alternately in the EDI load, regardless of the nature of the change in its electrical resistance. The frequency and duration of positive and negative discharge-pulse currents in the load can be the same or different, depending on the selected parameters of the elements of discharge circuits of the two CESs. The use of the developed method provides the formation of unipolar modes in the capacitors of each CES, which allows you to choose them for lower voltages, increase their life and reduce cost. In addition, with the same capacitance of the CESs, the total electric charge flowing in the load is practically zero after each even number of discharges. This significantly reduces the effect of electrochemical processes in the load, in particular the electrochemical destruction of the anode of the technological apparatus of the EDI, which inevitably occurs during the formation of unipolar pulse currents. The use of bipolar discharge currents in the EDI load also increases the stability of the discharge modes in the EDI due to the limitation of the duration of possible long aperiodic currents during the discharge of one of the CESs by the beginning of the counter current of the next discharge of the other CES. References 10, figures 3, table 1.

Magnetic fields in the workplace during the operation of contact spot welding installations

Contact welding is one of the most common types of welding. According to the technological method of obtaining joints, contact welding can be spot, relief, butt, suture. Spot contact welding a high productivity. Specialists use spot welding more often than other types of welding. The formation of permanent joints of materials occurs as a result of electric heating and deformation during compression. Workers warm up the products with pulses of alternating, direct or unipolar current of industrial frequency 50 Hz. Researchers have registered adverse factors at the welder's workplace that have an impact on health. These are high temperature, splashes and metal vapors, pulsed magnetic fields (PMF) of industrial frequency 50 Hz. The study aims to explore the levels of pulsed magnetic fields of industrial frequency of 50 Hz at workplaces during the operation of contact spot welding installations. The study included the study of the technology of contact spot welding, instrumental measurements and hygienic assessment of the levels of PMF of the industrial frequency of 50 Hz at the welders' workplaces during the operation of equipment in normal mode. Specialists have performed instrumental measurements of PMF levels with a TP2-2U milliteslameter during operation of three models of semi-automatic welding machines based on spot welding installations. The researchers recalculated the measured levels of magnetic field induction to the maximum operating current (Imax) possible during the technological process. Instrumental measurements showed that the magnetic field strength at the welders' workplaces depended on the type of installation, the distance from the radiation source, the localization of exposure, and welding of specific products. Experts registered the highest levels of magnetic fields in the arm area from 1096.0 to 5512.0 A/m. At the maximum operating current, the magnetic field strength can reach 13 678.0-11 024.0 A/m. The study showed that the intensity of pulsed magnetic fields of industrial frequency 50 Hz in the workplace can exceed the maximum permissible levels. To protect workers, it is necessary to limit the time of exposure to magnetic fields. Limitations. The studies are preliminary in nature and have limitations on the scope of the study.

The electrical model and harmonic characteristics of ZnO varistor considering unipoilar impulse aging polarity effect

The frequent and high amplitude unipolar impulse currents during the process of switching-on AC filter banks can accelerate the aging of arresters in some ultrahigh-voltage direct-current (UHVDC) and HVDC transmission systems, and result in polarity effect of zinc-oxide (ZnO) varistors. Hence, an improved ZnO varistor electrical model considering the polarity effect caused by unipolar impulse aging was proposed under power frequency voltage. Accelerated aging test under a negative polarity 15/35 µs impulse current was conducted on ZnO varistor samples to validate the proposed model. Furthermore, the current waveform and harmonic characteristics of the leakage current and its resistive component were simulated. Comparative analysis revealed that the simulation results were generally consistent with the test results. Based on the results, it's inferred that the variation of even-order harmonics are attributed to the polarity effect, and can be considered as one of the aging criterion of arresters.

The Tribological Behavior of Nanocrystalline TiO2 Coating Produced by Plasma Electrolytic Oxidation

Nanocrystalline TiO2 coatings were produced on titanium substrates using the plasma electrolytic oxidation technique. The effects of frequency, duty cycle, and type of applied current (pulse and direct) were evaluated on the microstructure of the coatings and the tribological behavior of the samples. Morphological evaluations demonstrated that the pancake structure was developed from coatings created with a unipolar pulsed current. However, a volcano-like surface morphology resulted from a constant current. The XRD analysis results showed that the coatings were composed mainly of the rutile phase by 77.80-96.34 wt. %. In comparison, 22.20 wt. % of the anatase phase was identified in samples produced with direct current. These phases were determined to be nanocrystalline (29.5-48.3 nm), which led to significant improvements in the tribological properties. The sample produced with direct current had larger pores, greater roughness, and a four-times higher thickness than samples created with unipolar current. Furthermore, the tribological study results showed that wear resistance was significantly higher in the unipolar pulsed current coatings than in those obtained with direct current. Moreover, samples made at a higher frequency and lower duty cycle showed better tribological behavior.

Switching Stability Analysis of Paralleled RC-IGBTs With Snapback Effect

In this article, a study of the snapback behavior of reverse conducting IGBTs (RC-IGBTs) by means of 2-D TCAD simulations is carried out. Half-cell TCAD models of 1200-V RC-IGBT structures with different snapback voltage levels were generated by varying the peak doping concentration of the punch-through N-buffer region. First observations show that snapback could be an issue for low current switching commutations of paralleled RC-IGBTs operating at low temperatures, where one device falls back into unipolar mode and current is completely misshared. Results show that the RC-IGBT snapback voltage level, circuit variations, and operating conditions play a critical role for determining whether the parallel RC-IGBTs operate in a stable or unstable mode.

On the Causes of the Slow Solar Wind: 1. The Solar Unipolar Induction Currents

AbstractThe cause of the solar wind is sought on a large‐scale (J × B) force resulting from the solar unipolar induction current, rather than coronal heating and small‐scale processes in the corona. In this paper, we consider the unipolar induction system considered by Alfven (1981, https://doi.org/10.1007/978-94-009-8374-8) the polar current (1.5 × 109 A) flowing out from the polar region of the sun spreads down longitudinally, which produces azimuthal magnetic fields. We considered two models, A and B. In Model A, the current spreads down fairly uniform in five divided regions of the heliosphere (rather than flowing only along the outer surface of the heliosphere). The resulting (J × B) force is mainly directed outward, causing an outward flow of the heliospheric plasmas. However, in this case, the speed at a distance of 1 AU is only 1 km/s, although the acceleration in each divided region is much greater than the solar gravity. In Model B, one third of the dynamo current is assumed to be concentrated in the area between 9.5 and 10.5 (where denotes the solar radius) and B = 10−6 T (103 nT) at 10 . The acceleration is estimated to be 1.4 × 102 m/s2 and the resulting speed at 1 AU is 200 km/s. Therefore, there is a possibility that the solar unipolar induction provides partially a new possibility for the cause of a slow, bulk flow of the solar wind.

Effects of various treatment procedures and pulse power modes on the photoelectric efficiency of Ti-PEO photocatalysts

In this study, various treatment methods were developed to achieve suitable structural phase control for the oxide layer of Ti plasma electrolytic oxidation (PEO) photocatalysts to improve their photoelectric conversion efficiency. To achieve the aforementioned purpose and to increase the doping efficiency, a three-stage PEO manufacturing procedure was developed and applied. In the first stage, the porous morphology and specific structural phases of a pretreated layer were controlled for doping preparation. In the second stage, doping elements were added into the surface and pores of the pretreated layer using the impregnation method. Finally, in the third stage, PEO was performed with different control parameters. The treatment factors in this study were the amount of manganese ion impregnation; the porosity, pore diameter, crystal structure, and carrier used in the treatment process; and the applied power mode. The effects of structural phase control, the Mn+ impregnation concentration, and the applied power modes on the carrier concentration were studied. The results indicated that the designed treatment method can effectively control the characteristics of oxide layers. By applying the impregnation method, the doping amount of Mn+ was increased more than five-fold compared with that in the single-step PEO treatment. Furthermore, to understand the treatment mechanism, the absorption spectrum, doping efficiency, Mn+ distribution, and mass transfer mechanism (of anions and cations) were investigated under direct, pulsed unipolar, and pulsed bipolar current. Finally, the functioning of the manufactured Mn: TiO2 (PEO) photocatalyst was verified with toluene under ultraviolet A, blue, and white LED light.

Phase composition of galvanic iron-nickel alloys obtained using pulsed current

The paper presents the results of studying the phase composition of iron-nickel alloys obtained by unsteady electrolysis. It was found that the use of a unipolar pulse current leads to a significant increase in the crystallization overvoltage at the crystallization front at the moment of the pulse action, which affects the component composition of the coatings. The phase composition of the alloys formed at the cathode differs from that shown in the iron-nickel equilibrium diagram.

Technology оf Safe Galvanochemical Process оf Strong Platings Forming Using Ternary Alloy

Established the possibility of galvanochemical obtaining of a plating stronger than in case of chrome precipitation. Proposed precipitation of ternary alloy Co-Мо-W, which allows using the effect of synergism. Proposed and researched usage instead of sulphate-anhydride electrolyte – citrate-diphosphate and ammonia-citrate one. Achieved an increase in current efficiency of precipitated alloy and decrease in current efficiency of hydrogen, with respect to chrome precipitation, which increased safety of the galvanochemical industry. Selected the optimal ratios of components in citrate-diphosphate and ammonia-citrate electrolytes for ternary alloy Co-Мо-W precipitation. Determined the parameters of electrical effect for the galvanic process: constant current – j = 2–8 А/dm2, pulse unipolar current – j = 4–20 А/дм2. Achieved a high microhardness of this plating and high adhesion to base surface. Achieved greater safety of the galvanochemical technological process of ternary alloy Co-Мо-W application compared with chromium plating.

A Hybrid-Arm Modular Multilevel Converters Topology With DC Low Voltage Operation and Fault Ride-Through Capability for Unidirectional HVDC Bulk Power Transmission

In this paper, a novel hybrid-arm modular multilevel converters (HA-MMCs) topology with DC low voltage operation and fault ride-through capability is proposed for unidirectional HVDC bulk power transmission. The HA-MMCs topology is a combination of two types of converter arms: the half-bridge sub-module based arm (HBSM-arm) and the diagonal bridge sub-module based arm (DBSM-arm). Replacing the traditional HBSM-MMC, the HA-MMCs are operated in current and reactive power control modes during normal conditions and can work as the rectifier or the inverter. Since the DBSM can provide bipolar voltages with unipolar currents, the HA-MMCs need not change its control strategy under DC low voltage conditions caused by the high-impedance faults. Under DC pole-to-pole or pole-to-ground faults, the HA-MMCs can both clear the DC fault current and work as the static synchronous compensator (STATCOM) to provide reactive power to support the AC grid. Compared with other MMC topologies with DC fault ride-through capability, the HA-MMCs topology is more economical for significantly decreasing the number of power devices. The operation states, control strategy and DC low voltage operation capability of the HA-MMCs are presented and simulation results of the LCC-HA-MMC hybrid system using PSCAD/EMTDC validate the characteristics and advantages of the HA-MMCs.

Characterization of electrical property and ion mobility in positive corona and dielectric barrier discharge with point to plane configuration

Atmospheric non-thermal plasma has been widely used. The aims of this research are to characterize electrical properties and charge carrier mobility of corona discharge and dielectric barrier discharge (DBD) plasma reactor with multiple points to plane configuration. Plasma was generated by DC high voltage and a 2 mm glass plate used as dielectric barrier covers passive electrode surface. Plasma current and voltage were measured using an analog multimeter and oscilloscope. Charge carrier mobility was calculated using Sigmond’s unipolar saturation current modified with multiple points to plane approach. Experiment result showed that electric current is proportional to squared voltage, in accordance to unipolar saturation current. Charge carrier mobilities obtained for corona and DBD were in range of 1,66 – 7,18 cm2/V.s and 0,331 – 0,848 cm2/V.s, respectively. Charge carrier mobility in DBD reactor increases with increasing distance between electrodes. Maximum charge carrier mobility in corona discharge was obtained at a distance of 1 cm, while in DBD at 4 cm.

Investigation of Different Iontophoretic Currents Profiles for Short-Term Applications in Cosmetics.

This study aimed at investigating the effect of electrical current profile upon the iontophoretic transport of (i) ascorbic acid (AA) and (ii) ellagic acid (EA), into porcine skin in vitro, and the impact of the physicochemical properties of both actives on their mechanism of transport when formulated in cosmetic compositions. The experiments were performed using a proprietary iontophoretic device containing a roller to apply the formulation. Three current profiles were tested: (i) galvanic direct current (DC), (ii) square unipolar pulse current (SPC), and (iii) galvanic direct current (DC) + pulse current (PC). The skin samples were collected at different sampling points, extracted and analyzed by HPLC. Results suggested that the DC + PC mode for only 5 min was able to significantly increase the delivery of AA from o/w cosmetic compositions. The use of this current profile might improve the skin penetration of AA due to electromigration and passive diffusion, the latter being facilitated by the physical enhancement method. The SPC mode significantly improved the passage of EA in its neutral form from cosmetic o/w formulations by electroosmosis. Tailoring specific electrical current modes considering the ionization state of active ingredients would allow the design of short and personalized cosmetic treatments that significantly improve the penetration efficiency of the active ingredients and possibly reduce the doses applied.

Beyond the Vestibulo-Ocular Reflex: Vestibular Input is Processed Centrally to Achieve Visual Stability.

The current study presents a re-analysis of data from Zink et al. (1998, Electroencephalography and Clinical Neurophysiology, 107), who administered galvanic vestibular stimulation through unipolar direct current. They placed electrodes on each mastoid, and applied both right and left anodal stimulation. Ocular torsion and visual tilt were measured under different stimulation intensities. New modelling introduced here demonstrates that directly proportional linear models fit reasonably well to the relationship between vestibular input and visual tilt, but not to that between vestibular input and ocular torsion. Instead, an exponential model characterised by a decreasing slope and an asymptote fitted best. These results demonstrate that in the results presented by Zink et al., ocular torsion could not completely account for visual tilt. This suggests that vestibular input is processed centrally to stabilise vision when ocular torsion is insufficient. Potential mechanisms and seemingly conflicting literature are discussed.

Beyond the Vestibulo-Ocular Reflex: Vestibular Input is Processed Centrally to Achieve Visual Stability

The current study presents a re-analysis of data from Zink et al. (1998, Electroencephalography and Clinical Neurophysiology, 107), who administered galvanic vestibular stimulation through unipolar direct current. They placed electrodes on each mastoid and applied either right or left anodal stimulation. Ocular torsion and visual tilt were measured under different stimulation intensities. New modelling introduced here demonstrates that directly proportional linear models fit reasonably well with the relationship between vestibular input and visual tilt, but not to that between vestibular input and ocular torsion. Instead, an exponential model characterised by a decreasing slope and an asymptote fitted best. These results demonstrate that in the results presented by Zink et al. (1998), ocular torsion could not completely account for visual tilt. This suggests that vestibular input is processed centrally to stabilise vision when ocular torsion is insufficient. Potential mechanisms and seemingly conflicting literature are discussed.

Systematic motion of magnetic domain walls in notched nanowires under ultrashort current pulses

The precise manipulation of transverse magnetic domain walls in finite/infinite nanowires with artificial defects under the influence of very short spin-polarized current pulses is investigated. We show that for a classical $3d$ ferromagnet material like Nickel, the exact positioning of the domain walls at room temperature is possible only for pulses with very short rise and fall time that move the domain wall reliably to nearest neighboring pinning position. The influence of the shape of the current pulse and of the transient effects on the phase diagram current-pulse length are discussed. We show that large transient effects appear even when $\alpha$=$\beta$, below a critical value, due to the domain wall distortion caused by the current pulse shape and the presence of the notches. The transient effects can oppose or amplify the spin-transfer torque (STT), depending on the ratio $\beta/\alpha$. This enlarges the physical comprehension of the DW motion under STT and opens the route to the DW displacement in both directions with unipolar currents.