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Plasma electrolytic polishing (PeP) is mainly used to improve the surface quality and thus the performance of electrically conductive parts. It is usually used as an anodic process, i.e., the workpiece is positively charged. However, the process is susceptible to high current peaks during the formation of the vapour–gaseous envelope, especially when polishing workpieces with a large surface area. In this study, the influence of the anode immersion speed on the current peaks and the average power during the initialisation of the PeP process is investigated for an anode the size of a microreactor mould insert. Through systematic experimentation and analysis, this work provides insights into the control of the initialisation process by modulating the anode immersion speed. The results clarify the relationship between immersion speed, peak current, and average power and provide a novel approach to improve process efficiency in PeP. The highest peak current and average power occur when the electrolyte splashes over the top of the anode and not, as expected, when the anode touches the electrolyte. By immersion of the anode while the voltage is applied to the anode and counterelectrode, the reduction of both parameters is over 80%. [ABSTRACT FROM AUTHOR]

This study proposes a topology structure for a flyback grid-connected inverter with a compensation capacitor. The addition of the compensation capacitor structure increases the harmonic oscillation period and reduces the switching frequency. Additionally, a control strategy for the microinverter is proposed. By using an accurate peak current reference curve, the system ensures precise turn-off signals, thus reducing the harmonic content of the grid-connected current. Simultaneously, the multi-valley turn-on strategy is employed to address the issue of high switching frequency, minimising the impact of energy. The proposed topology structure and control methods are modelled, simulated, and tested to validate the feasibility of the microinverter topology structure and the effectiveness of the control strategy, achieving a maximum efficiency of 95.2% and controlling the total harmonic distortion (THD) below 2.39%. Compared to other microinverter products, it is more efficient and stable. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, a novel AA7075-TiO2 metal matrix composite was machined utilizing a biosilica mixed EDM technique and the surface roughness and material removal rate are optimized. The biosilica particles are produced from waste maize cobs and then silane-treated. The optimization of process variables wasperformed using Taguchi grey relational approach with a process variable of peak current, gap voltage and pulse-on time. Results revealed that the gap voltage is the most important process variable, since it has a larger max-min difference of 0.25. In order to create a high MRR of 11.6mm3/min and a surface roughness of 2.25 m, the maximum GRG of 0.79 for Trial 1 (A2B1C3) represents the most ideal process variable group. The best results appear to be obtained with a peak current of 10 A, a gap voltage of 20V, and a pulse-on time of 140μs. The new GRG, however, is around 2.51% better than the anticipated optimized process variables of A2B1C3 with an old GRG of 0.79, according to the confirmation research. The new MRR of 11.89mm3/min and the surface roughness of 2.30s with a GRG of 0.81 are based on the optimized new process variables (A1B1C3). [ABSTRACT FROM AUTHOR]

The need for innovative materials has increased in the current era of research and technology. Advanced materials such as shape memory alloys are in great supply in the industrial and commercial sectors. It is a unique and very uncommon metal alloy that can regain its original shape after being subjected to extremely low temperatures. SMAs may be classified as NiTi-based, Cu-based, or Fe-based depending on the metal-combination. Alloys based on copper have excellent elasticity and damping properties that allow them to withstand a broad variety of temperatures. Using the EDM method, this research investigates the effects of Ton, Toff, Ip, and GV on SR and dimensional deviation. 8.87 mm and 4.79 mm are the greatest and lowest values of SR that can be found, respectively. The dimensional deviation ranges from 0.03 mm to 0.28 mm, with a minimum value of 0.03 mm. Ton and Ip have a greater influence on surface roughness than Toff and GV. Images from SEM of workpiece samples show the production of micro-cracks as-well-as macro-ridges on the surface of the sample during EDM operations. SEM micrographs depicted the deviation in the dimensions of the workpiece samples after EDM operations on Cu-based SMA samples. [ABSTRACT FROM AUTHOR]

Elves are observed as expanding rings of light in the UV and visible optical bands. They are produced when electromagnetic pulses from lightning discharges interact with the lower parts of the ionosphere. Elves are well known to be associated with high peak current lightning discharges. Here, we use data from the Modular Multi‐spectral Imaging Array (MMIA) of the Atmosphere‐Space Interactions Monitor (ASIM), and search for observations of Elves when high peak current lightning discharges are detected by Vaisala's Global Lightning Detection network GLD360. We present two groups of events; high peak current detections associated with Elves and high peak current detections not associated with Elves. To understand why some current pulses with high peak currents do not produce observable Elves, we investigate and compare the lightning activity occurring before these two types of events, in terms of both the number of lightning discharges detected by GLD360 and the peak currents of the preceding discharges. Our results, using data from GLD360, suggest that current pulses with peak currents above |120| kA tend to produce Elves nearly always, regardless of the preceding lightning activity. For current pulses with peak currents between |70| and |120| kA, the number of observed Elves might be affected by the preceding lightning activity, or is the result of the characteristics of the storm cells that produce the Elve. Plain Language Summary: There are many different phenomena that occur above active thunderstorms. Among these phenomena are Elves, which are observed as expanding rings of light (in UV and visible light) that are produced when powerful lightning pulses interact with the ionosphere at altitudes around 90 km. Elves are produced by strong electromagnetic waves from lightning pulses. We explore two sets of events in this study; strong lightning pulses that produce Elves, and strong lightning pulses that do not produce Elves. To understand why some strong pulses do not produce Elves, we investigate the lightning activity occurring before these events. We find that for lightning pulses with peak currents between |70| and |120| kA, the preceding lightning activity may affect whether an Elve is produced or not. Key Points: We present two types of events; high peak current lightning associated with Elves, and high peak current lightning not associated with ElvesFor peak currents >120 kA the probability of producing an Elve is more than 95%For peak currents between 70 and 120 kA, previous lightning activity may influence whether an Elve is produced or not [ABSTRACT FROM AUTHOR]

BACKGROUND: The experimental process for optimizing microbial fuel cell (MFC) design under different electrode geometries is restricted. An MFC can be defined as a bio‐electrochemical system (BES) that facilitates the direct conversion of the chemical energy stored in organic matter into electrical energy by harnessing the metabolic activity of microorganisms. Computational fluid dynamics (CFD) tools allow the simulation and evaluation of electro‐analysis phenomena such as cyclic voltammetry and chemical reactions, which can help the optimization of the BESs. In this study, MFC is designed to provide the maximum peak current and efficiency for the applied voltage on various working (or anode) electrode geometries (i.e. hexagonal, square, pentagonal, circular, triangular, rectangular, and rhombus). RESULTS: The CFD simulation results demonstrate that a configuration with a larger perimeter value and surface area (i.e. hexagonal design) of the working electrode shows a higher peak current (2422.75 mA) than other configurations. The experimental findings supported the simulation result and reveal that a hexagonal electrode containing a MFC setup produces a maximum power density of 22.41 ± 0.32 mW m−3 and a current density of 41.58 ± 0.35 mA m−2. The MFC operation demonstrated adequate bioelectricity generation of 540 ± 03 mV on Day 4 of operation at 1000 Ω. Additionally, maximum reduction in chemical oxygen demand (76.13 ± 0.5%) and coulombic efficiency (76.03 ± 0.4%) was achieved for synthetic wastewater using a hexagonal MFC. CONCLUSION: Based on these fundamental discoveries, the CFD simulation and its experimental validation considerably drag focus toward the possibility of employing COMSOL Multiphysics software for system improvement of different MFC system applications. © 2023 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Plasma electrolytic polishing (PeP) is mainly used to improve the surface quality and thus the performance of electrically conductive parts. It is usually used as an anodic process, i.e., the workpiece is positively charged. However, the process is susceptible to high current peaks during the formation of the vapour–gaseous envelope, especially when polishing workpieces with a large surface area. In this study, the influence of the anode immersion speed on the current peaks and the average power during the initialisation of the PeP process is investigated for an anode the size of a microreactor mould insert. Through systematic experimentation and analysis, this work provides insights into the control of the initialisation process by modulating the anode immersion speed. The results clarify the relationship between immersion speed, peak current, and average power and provide a novel approach to improve process efficiency in PeP. The highest peak current and average power occur when the electrolyte splashes over the top of the anode and not, as expected, when the anode touches the electrolyte. By immersion of the anode while the voltage is applied to the anode and counterelectrode, the reduction of both parameters is over 80%.

The study of pressure stimulated current (PSC) changes of rocks is significant to monitor dynamic disasters in mines and rock masses. The existing studies focus on change laws and mechanism of currents generated under the loading of rocks. An electrical and mechanics test system was established in this paper to explore the impacts of loading rates on PSCs. The results indicated that PSC curves of different rocks had different change laws under low/high loading rates. When the loading rate was relatively low, PSC curves firstly changed gently and then increased exponentially. Under high loading rates, PSC curves experienced the rapid increase stage, gentle increase stage and sudden change stage. The compressive strength could greatly affect the peak PSC in case of rock failure. The loading rate was a key factor in average PSC. Under low loading rates, the variations of PSCs conformed to the damage charge model of fracture mechanics, while they did not at the fracture moment. Under high loading rates, the PSCs at low stress didn’t fit the model due to the stress impact effects. The experimental results could provide theoretical basis for the influence of loading rates on PSCs.

The effect of spacer layers on electron transport through two-barrier nanostructures was studied using the numerical solution of the time-dependent Schrodinger–Poisson equations with exact discrete open boundary conditions. The formulation of the problem took into account both the active region consisting of a quantum well and barriers, as well as the presence of highly doped contact layers and spacer layers. The use of the time formulation of the problem avoids the divergence of the numerical solution, which is usually observed when solving a stationary system of the Schrodinger–Poisson equations at small sizes of spacer layers. It is shown that an increase in the thickness of the emitter spacer leads to a decrease in the peak current through the resonant tunneling nanostructures. This is due to the charge accumulation effects, which, in particular, lead to a change in the potential in an additional quantum well formed in the emitter spacer region when a constant electric field is applied. The valley current also decreases as the thickness of the emitter spacer increases. The peak current and valley current are weakly dependent on the thickness of the collector spacer. The collector spacer thickness has a strong effect on the applied peak and valley voltages. The above features are valid for all three different resonant tunneling nanostructures considered in this study. For the RTD structures based on Al0.3Ga0.7As/GaAs, the optimized peak current value Ipmax = 5.6 × 109 A/m2 and the corresponding applied voltage Vp = 0.44 V. For the RTD structures based on AlAs/In0.8Ga0.2As, Ipmax = 14.5 × 109 A/m2 (Vp = 0.54 V); for RTD structures based on AlAs/In0.53Ga0.47As, Ipmax = 45.5 × 109 A/m2 (Vp = 1.75 V). [ABSTRACT FROM AUTHOR]

Distributed power generation plays a critical role in the stability and reliability of modern power systems. Due to the rapid growth of renewable energy generation, the requirements of the transmission and distribution system operators are becoming more stringent. Among these requirements, one of the most important is the Low-Voltage Ride-Through (LVRT) capability, which demands that the inverters remain connected to the grid and provide support during voltage sags. For this purpose, flexible current control algorithms stand out because they can manage unbalanced voltages and simultaneously achieve other control objectives. With the aim of presenting a concrete document focused on describing fundamental principles and discussing common design guidelines, this paper presents an overview of flexible current control strategies applied to LVRT capability. The operation features and design aspects of experiences reported in the literature are reviewed. Moreover, the paper proposes a general methodology to design LVRT flexible current control algorithms. Finally, current and future trends are discussed. [ABSTRACT FROM AUTHOR]

Wire-Electric Discharge Machining (W-EDM) is one of viable advanced machining techniques for machining of hard materials like Titanium alloys precisely. It is critical to determine the optimum settings for control parameters to achieve desired levels of surface finish and dimensional tolerance. Considering this, this research investigates the effects of current, pulse on time (Ton) and pulse off time (Toff) on surface roughness (Ra) of WED machined Ti-6Al-4V alloy. The study showed that, increase in current from 2 A to 6 A resulted in increase of Ra by 13.92 % and increase in Ton from 20 μs to 50 μs caused an almost linear increase in Ra by 8.95 %. But increase in Toff from 20 μs to 30 μs led to a sharp reduction in Ra by about 20.44 %. Further, a regression model is developed to predict the surface roughness with R2=72.5%. The machined surfaces are characterised by the presence voids and microcracks on the recast layers, formation of microglobules, ridges and craters due to thermal effects. Within the range of study Toff showed significantly larger influence on Ra compared to other parameters of the study. [ABSTRACT FROM AUTHOR]

304 stainless steel, which is widely used in the industrial field due to its excellent thermostability, corrosion resistance, and welding performance, was welded using local dry underwater pulse metal inert gas (LDU-PMIG) welding technology in this study. The effect of different pulse peak currents on droplet transfer behavior and weld formation was investigated. The results show that short circuit transfer, globular transfer, and projected transfer were observed in the LDU-PMIG process. With the peak current of 240 A, the droplet transfer modes were short-circuit transfer and globular transfer; the weld formation was irregular with large particle spatters around the weld. With the peak current increased to 260 A, the droplet transfer mode changed into the globular transfer, and the weld formation quality was improved. With the peak current of 280 A, the droplet transfer mode was projected transfer, the weld formation was satisfied with a few spatters, and the coefficient of weld formation was the largest, and projected transfer was the most stable mode. With the increase of the peak current from 300 to 320 A, the droplet transfer mode did not change, but the instability of the welding arc resulted in poor weld formation with serious spatters and undercuts. [ABSTRACT FROM AUTHOR]

The greater number of electrostatic discharges (ESDs) that occur in nature is by air rather than by contact. However, due to low reproducibility in the current of air discharges, the IEC 61000-4-2 defines that the current's calibration of an ESD gun must be made only for contact discharges. In the work presented here, there is an attempt to improve the poor reproducibility of air discharges by a significant observation derived from ESD measurements and, more specifically, the relationship between the rise time and the peak current for every ESD gun. This fact validated in this paper from current measurements of two different ESD guns will help all who are involved in ESD measurements in EMC laboratories by reducing the existing uncertainty in measurements of air discharges. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article presents the electric field waveforms of natural return strokes recorded by Foshan Total Lightning Location System. The distance ranges from 10 to 300 km. The evolution of parameters for positive first and negative first and subsequent return stroke electric field waveforms along with distance change is analyzed. The results show that the risetime, fall time, half-peak width, and zero-crossing time become longer with longer distance, and these four parameters of the negative return strokes show more clear linear relation with distance than the positive return strokes. For the overshoot duration, the values for both positive and negative return strokes increase with distance at 10–200 km, but when the distance is larger, the distance dependence becomes less obvious. The values of the initial peak normalized to 100 km and 20 kA remain the same in general for all the return strokes. For the overshoot amplitude and the ratio of overshoot to initial peak, the values for both positive and negative return strokes increase with distance. The return stroke electric field waveforms at far distances are more likely to show clear opposite polarity overshoot. [ABSTRACT FROM AUTHOR]

In this work, new electrochemical sensors based on the modification of glassy carbon electrode (GCE) with multiwalled carbon nanotubes (MWCNTs)—rare metal oxides (REMO) nanocomposites were fabricated by drop-to-drop method of MWCNTs-REMO dispersion in ethanol. REMO nanoparticles were synthesized by precipitation followed by hydrothermal treatment at 180 °C in absence and presence of TritonTM X-100 surfactant. Cyclic voltammetry (CV) analysis using MWCNTs-CeO2@GCE and MWCNTs-Yb2O3@GCE sensors were used for the analysis of sulfisoxazole (SFX) drug in water samples. The results of CV analysis showed that MWCNTs-REMO@GCE sensors have up to 40-fold higher sensitivity with CeO2 compared to the bare GCE sensor. The estimated values of the limit of detection (LoD) of this electrochemical sensing using MWCNTs-CeO2@GCE and MWCNTs-Yb2O3@GCE electrodes reached 0.4 and 0.7 μM SFX in phosphate buffer pH = 7, respectively. These findings indicate that MWCNTs-REMO@GCE electrodes are potential sensors for analysis of sulfonamide drugs in water and biological samples. [ABSTRACT FROM AUTHOR]

The temperature dependence of the peak pulse current ${I}_{\text {peak}}$ and the current rising rate di / dt of the insulated gate trigger thyristors (IGTTs) is studied for the first time in this article. Based on the theoretical analysis of the material properties and device physical parameters including the net injection efficiency $\gamma $ and pulse damping parameter ${k}$ of IGTTs, the temperature dependence is systematically modeled. The mechanism underlying the effect of injection enhancement on the alleviation of performance deterioration at elevated temperatures is discussed. Experiments of single and repetitive capacitive pulse discharge at $- 40\,\,^{\circ }\text{C}$ to 125 °C are carried out on IGTTs with enhanced carrier injection (E-IGTTs) and conventional IGTTs (C-IGTTs). Both the measurement and calculation have shown consistent results that the E-IGTTs with higher $\gamma $ can exhibit higher ${I}_{\text {peak}}$ and di / dt and lower temperature coefficients at $- 40\,\,^{\circ }\text{C}$ to 125 °C compared with C-IGTTs. Lower energy loss on E-IGTTs also alleviates the self-heating effect in repetitive pulse discharge operations. Enhancing the injection efficiencies is an effective way to reduce the temperature dependence of pulsed power performance of IGTTs. [ABSTRACT FROM AUTHOR]

Due to the contradiction between [ABSTRACT FROM AUTHOR]

Negative differential resistance (NDR) devices are significant for logic, memory and radiofrequency applications. Herein, we study the electronic and quantum transport properties of “cold” metals 2H MX2 (M = Nb, Ta; X = S, Se) and their heterojunction (HJ) NDR diodes. Owing to the energy gaps of such 2H MX2 close to the Fermi level, the broken-gap structure can be formed by the MSe2/MS2 HJs. A favorable peak current thus is achieved benefitting from the large conductivity of metallic 2H MSe2/MS2 HJs. The promising peak-valley ratio PVR (51) and peak current ($5.1\times 10^{4} \mu \text{A}/\mu \text{m}$) is obtained by edge contact NbSe2/NbS2 HJ NDR device. The study of “cold” metal NDR performance provides a practical solution for NDR devices to achieve desired PVR and peak currents simultaneously. [ABSTRACT FROM AUTHOR]

Unbalanced grid voltage sags are the severe challenge for wind power generation system which connected to the grid successfully. The dc bus voltage and output power will fluctuate under unbalanced grid voltage. Moreover, the voltage sags will lead to the increase of peak current, which will bring potential safety hazards to the operation of wind power system. This paper proposes a simple current limiting control scheme without auxiliary equipment, which based on the detailed analysis of the excessive peak current. In this scheme, the machine side converter (MSC) controller adjusts the electromagnetic power according to the power transmitted to the grid by the grid side converter (GSC). Meanwhile, it converts the unbalanced power on the dc-link into the rotor kinetic energy, avoiding the dc-link overvoltage. The GSC controller can not only ensure that the three-phase inverter currents are in the maximum safe range that the converters can bear, but also provide reactive power support for the grid. Furthermore, the fluctuations on dc bus voltage and output power can be eliminated effectively by using the GSC controller. The feasibility of the proposed scheme and the superiority over the traditional control schemes have been verified by simulations under different types of unbalanced voltage.

Wire electric discharge machining (WEDM) is one of the foremost methods which has been utilized for machining hard-to-cut materials like Titanium alloys. However, there is a need to optimize their important operating parameters to achieve maximum material removal rate (MRR). The present paper investigates the effect of control factors like current, pulse on time (Ton), pulse off time (Toff) on MRR of machining of Ti-6Al-4V alloy. The study showed that, increase in current from 2 A to 6 A results in a significant increase in MRR by 93.27% and increase in Ton from 20 μs to 35 μs improved the MRR by 7.98%, beyond which there was no improvement of MRR. The increase in Toff showed a counterproductive effect. Increase in Toff from 10 μs to 30 μs showed an almost linear decrease in MRR by 52.77%. Morphological study of the machined surface showed that cut surface consists of recast layer on which microcracks were present, and revealed the presence of globules, ridge-structured formations of recast layers and voids. In addition, a regression model was developed to predict the MRR with respect to the control factors, which showed a good prediction with an R2 value of 99.67%. [ABSTRACT FROM AUTHOR]

The effect of spacer layers on electron transport through two-barrier nanostructures was studied using the numerical solution of the time-dependent Schrodinger–Poisson equations with exact discrete open boundary conditions. The formulation of the problem took into account both the active region consisting of a quantum well and barriers, as well as the presence of highly doped contact layers and spacer layers. The use of the time formulation of the problem avoids the divergence of the numerical solution, which is usually observed when solving a stationary system of the Schrodinger–Poisson equations at small sizes of spacer layers. It is shown that an increase in the thickness of the emitter spacer leads to a decrease in the peak current through the resonant tunneling nanostructures. This is due to the charge accumulation effects, which, in particular, lead to a change in the potential in an additional quantum well formed in the emitter spacer region when a constant electric field is applied. The valley current also decreases as the thickness of the emitter spacer increases. The peak current and valley current are weakly dependent on the thickness of the collector spacer. The collector spacer thickness has a strong effect on the applied peak and valley voltages. The above features are valid for all three different resonant tunneling nanostructures considered in this study. For the RTD structures based on Al0.3Ga0.7As/GaAs, the optimized peak current value Ipmax = 5.6 × 109 A/m2 and the corresponding applied voltage Vp = 0.44 V. For the RTD structures based on AlAs/In0.8Ga0.2As, Ipmax = 14.5 × 109 A/m2 (Vp = 0.54 V); for RTD structures based on AlAs/In0.53Ga0.47As, Ipmax = 45.5 × 109 A/m2 (Vp = 1.75 V).

Distributed power generation plays a critical role in the stability and reliability of modern power systems. Due to the rapid growth of renewable energy generation, the requirements of the transmission and distribution system operators are becoming more stringent. Among these requirements, one of the most important is the Low-Voltage Ride-Through (LVRT) capability, which demands that the inverters remain connected to the grid and provide support during voltage sags. For this purpose, flexible current control algorithms stand out because they can manage unbalanced voltages and simultaneously achieve other control objectives. With the aim of presenting a concrete document focused on describing fundamental principles and discussing common design guidelines, this paper presents an overview of flexible current control strategies applied to LVRT capability. The operation features and design aspects of experiences reported in the literature are reviewed. Moreover, the paper proposes a general methodology to design LVRT flexible current control algorithms. Finally, current and future trends are discussed.

Abstract We present sub‐microsecond‐scale, high‐speed video camera observations of three negative stepped leaders in cloud‐to‐ground flashes with return‐stroke peak currents (estimated by the U.S. National Lightning Detection Network) of −17, −104, and −228 kA. The camera frame exposure times for these observations were 1.8, 1.0, and 0.74 µs, respectively. The 0.74 µs exposure time is the shortest reported to date. We observed the temporal and spatial evolution of space leaders from their inception to their attachment to the pre‐existing leader channel (PELC). For stepped leaders that led to return strokes having higher peak currents, the space leaders appear to have incepted at farther median two‐dimensional distances from their respective PELC‐attachment points. These median distances were 6.1, 16.6, and 17.6 m, respectively, for the three strokes. Our observations indicate that space leader characteristics are likely influenced by stepped‐leader line‐charge‐density, which is expected to be higher in strokes with higher return‐stroke peak currents.

We present sub‐microsecond‐scale, high‐speed video camera observations of three negative stepped leaders in cloud‐to‐ground flashes with return‐stroke peak currents (estimated by the U.S. National Lightning Detection Network) of −17, −104, and −228 kA. The camera frame exposure times for these observations were 1.8, 1.0, and 0.74 µs, respectively. The 0.74 µs exposure time is the shortest reported to date. We observed the temporal and spatial evolution of space leaders from their inception to their attachment to the pre‐existing leader channel (PELC). For stepped leaders that led to return strokes having higher peak currents, the space leaders appear to have incepted at farther median two‐dimensional distances from their respective PELC‐attachment points. These median distances were 6.1, 16.6, and 17.6 m, respectively, for the three strokes. Our observations indicate that space leader characteristics are likely influenced by stepped‐leader line‐charge‐density, which is expected to be higher in strokes with higher return‐stroke peak currents. Plain Language Summary: Lightning and thunderstorm activity have extremely important socio‐economic impacts including on power transmission and distribution, severe weather prediction, lightning safety and protection, management of outdoor events, airport and maritime activities, air travel, and space launches. The vast majority of lightning occurring between thunderclouds and the Earth's surface effectively transfer negative charge to ground. In such discharges, the first negatively charged channel (called a leader) proceeds from the thundercloud to ground in a stepwise fashion, pausing for fractions of a second after each step, before reaching ground. Many questions remain about the detailed mechanism of negative cloud‐to‐ground stepped‐leader progression and how natural lightning leaders compare to those in long sparks in laboratory experiments. We observed sub‐microsecond‐scale processes that lead to the formation and progression of negative cloud‐to‐ground lightning leader channels. Our study presents a detailed characterization of space leaders, a region of super‐heated plasma just ahead of the negative leader tip, that forges a path forward for the first stroke in cloud‐to‐ground lightning. Results of this study help explain why negative leaders pause between bursts of rapid acceleration. Key Points: Median space‐leader maximum 2‐D lengths and inception‐to‐attachment‐point distances are longer in higher peak‐current return strokesHigher stepped‐leader line‐charge‐densities in strokes with higher return‐stroke peak currents influence space‐leader characteristicsLeader‐step lengths and speeds are affected by the varying electric field environments at different altitudes above ground [ABSTRACT FROM AUTHOR]

A three-phase four-wire inverter is highly suitable for low-voltage distributed grids owing to its zero sequence control; however, essential aspects of grid-following inverters during faults, such as the power oscillation control flexibility and power injection capability, are rarely discussed in detail. Thus, by introducing zero sequence instantaneous power into a four-wire system, this article proposes a flexible control strategy that enhances the power injection capability of the inverter in the photovoltaic generation system during asymmetrical grid faults. First, a generalized reference current generation with flexible control of positive, negative, zero sequence current (FPNZSC), and power oscillations is presented. Second, a maximum allowable power injection (MAPI) algorithm based on the actual value constraints of power oscillations and peak current is presented according to the requirement. The proposed MAPI-FPNZSC strategy further extends the existing fault ride through methods in three-wire inverter systems, which is also suitable for single line-to-ground and double line-to-ground faults and can be easily realized in the natural or stationary frame. The effectiveness of the proposed strategy is verified by comparing the provided three typical objectives with the traditional method, and tested in a real-time hardware-in-the loop experimental platform. [ABSTRACT FROM AUTHOR]

The triangulation of red sprites was obtained, based on concurrent observations over a mesoscale convective system (MCS) in North China from two stations separated by about 450 km. In addition, broadband sferics from the sprite-producing lightning were measured at five ground stations, making it possible to locate and identify the individual causative lightning discharges for different elements in this dancing sprite event. The results of our analyses indicate that the sprites were produced above the trailing stratiform region of the MCS, and their parent strokes were located mainly in the peripheral area of the stratiform. The lateral offset between sprites and causative strokes ranges from a few km to more than 50 km. In a particularly bright sprite, with a distinct halo feature and streamers descending down to an altitude of approximately 48 km, the sprite current signal identified in the electric sferic, measured at a range of about 1,110 km, peaked at approximately 1 ms after the return stroke.

Natural cloud-to-ground (CG) lightning behaves differently over land and ocean. These differences likely reflect local variations in the speed at which storms develop over ocean, and are possibly contributed to by differences in the local aerosol composition. Earlier studies have reported statistically larger peak currents for negative CG first strokes over ocean than over land. This work focuses on differences in this relationship for first strokes, for subsequent strokes in existing channels to ground, and for subsequent strokes creating new ground contacts. This distinction will shed light on the mechanism responsible for the observed land:ocean differences, and can either support or refute the hypothesis that this difference is associated with the propagation of downward negative leaders in free space, driven by the vertical profile of electric field within and below the cloud. Results show that when compensated for detection threshold increases with increasing distance from land-based sensors, the distribution of estimated peak currents for subsequent strokes in existing (pre-ionized) channels to ground was indistinguishable from distributions for lightning that occurred inland, near shore, offshore, and in the distant ocean (~200 km offshore), with median values ranging between 14.4 and 15.1 kA. Conversely, the population of first strokes over distant ocean had much higher peak currents than those that occurred inland (median values of 23.1 kA vs. 17.3 kA, respectively), when corrected for detection threshold. These findings are consistent with the field-profile hypothesis noted above since peak currents for return strokes due to downward leaders that establish new channels (first strokes) would be impacted the most by the vertical profile of electric field near the cloud base, whereas the peak current for strokes in previously-established channels should be far less dependent on the field profile.

Forest fire danger predicting models should have information about the return-stroke peak current of lightning strokes. The purpose of this work is to obtain statistical characteristics of the return-stroke peak current of lightning strokes recorded by WWLLN in the Republic of Buryatia (Russian Federation). The Republic of Buryatia has a mountainous relief. Orography influences the physical conditions for the formation of thunderclouds. The originality of the research is determined by the analysis of the distributions of the return-stroke peak current for lightning discharges over different altitude zones of the Buryatia. Similar studies have been carried out, for example, for the territories of the North Caucasus, Germany, and the USA. Digital elevation model SRTMGL3 and free geoinformation software QGIS and GRASS have been used for statistical and spatial analysis. The calculation of the statistical characteristics and the construction of distributions have been performed for 171,900 lightning discharges registered by WWLLN. The average current has been ~ 69 kA, the median has been ~ 43 kA, with an average power error of 9%. For 84% of lightning discharges, the current does not exceed 100 kA. An increase in the current of lightning discharges with an increase in altitude above sea level has been noted. The average amperage and the median, are ~ 57 kA and ~ 39 kA for low mountains (less than 1000 m), ~ 70 kA and ~ 43 kA for middle mountains (from 1000 to 2000 m), and ~ 100 kA and ~ 56 kA for high mountains (more than 2000 m), respectively. The results obtained can be used to predict and assess the forest fire danger. [ABSTRACT FROM AUTHOR]

When a lightning strikes a high object, the current flows along the object and produces in this way a field component additional to the field radiated from the lightning channel. This additional field component enhances the field compared to lightning to flat ground. In this article, the field enhancement is analyzed for lightning striking the Peissenberg Tower, Germany. The analysis is based on investigations of the far field at distances from 10 to 1000 km. In the computer simulations, the return stroke process is taken into account with the transmission line (TL)-model and the tower is modelled with the computer program CONCEPT II based on the method of moments. In a first step, the pure effect of the tower is analyzed. In this case, the ground is taken into account as perfectly conducting plane. In the next step, the effect of the field propagation is added by introducing an attenuation function based on the solution of Sommerfeld and a far-field approximation of Norton. For fast rising return stroke currents and relatively near distances between 10 and 30 km, the field enhancement may exceed 100%. The field enhancement decreases strongly with decreasing soil conductivity (σ) and increasing distance (s), while the influence of the permittivity (ϵ) is rather small. At a distance of more than 100 km the field enhancement is typically in the range of some tens of percent. This result agrees well with the data of the European lightning location system EUCLID. From EUCLID an average field enhancement of about 20% is reported for lightning striking the Peissenberg Tower. [ABSTRACT FROM AUTHOR]

In this work, new electrochemical sensors based on the modification of glassy carbon electrode (GCE) with multiwalled carbon nanotubes (MWCNTs)—rare metal oxides (REMO) nanocomposites were fabricated by drop-to-drop method of MWCNTs-REMO dispersion in ethanol. REMO nanoparticles were synthesized by precipitation followed by hydrothermal treatment at 180 °C in absence and presence of TritonTM X-100 surfactant. Cyclic voltammetry (CV) analysis using MWCNTs-CeO2@GCE and MWCNTs-Yb2O3@GCE sensors were used for the analysis of sulfisoxazole (SFX) drug in water samples. The results of CV analysis showed that MWCNTs-REMO@GCE sensors have up to 40-fold higher sensitivity with CeO2 compared to the bare GCE sensor. The estimated values of the limit of detection (LoD) of this electrochemical sensing using MWCNTs-CeO2@GCE and MWCNTs-Yb2O3@GCE electrodes reached 0.4 and 0.7 μM SFX in phosphate buffer pH = 7, respectively. These findings indicate that MWCNTs-REMO@GCE electrodes are potential sensors for analysis of sulfonamide drugs in water and biological samples.

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This study considers the effect of wire electro discharge machining (WEDM) parameter peak current (Ip) and pulse peak voltage (Vp) on the machined surface morphology of TiNiCu shape memory alloys. Various defects of machined surfaces were identified and correlated with parameter values and measured average surface roughness (Ra) and average surface depth (Rz). It was found that the nature of the machined surface is highly influenced by the nature of sparking, which is dictated by levels of peak current and peak voltage used during machining. Distinctions between machining parameters resulting in "rough-cut" and "trim-cut" machining are reported along with deviations in output responses, which counters the trend reported in the literature. [ABSTRACT FROM AUTHOR]