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Here we report a comprehensive numerical study for the operating behavior and physical mechanism of nitride micro-light-emitting-diode (micro-LED) at low current density. Analysis for the polarization effect shows that micro-LED suffers a severer quantum-confined Stark effect at low current density, which poses challenges for improving efficiency and realizing stable full-color emission. Carrier transport and matching are analyzed to determine the best operating conditions and optimize the structure design of micro-LED at low current density. It is shown that less quantum well number in the active region enhances carrier matching and radiative recombination rate, leading to higher quantum efficiency and output power. Effectiveness of the electron blocking layer (EBL) for micro-LED is discussed. By removing the EBL, the electron confinement and hole injection are found to be improved simultaneously, hence the emission of micro-LED is enhanced significantly at low current density. The recombination processes regarding Auger and Shockley–Read–Hall are investigated, and the sensitivity to defect is highlighted for micro-LED at low current density.Synopsis: The polarization-induced QCSE, the carrier transport and matching, and recombination processes of InGaN micro-LEDs operating at low current density are numerically investigated. Based on the understanding of these device behaviors and mechanisms, specifically designed epitaxial structures including two QWs, highly doped or without EBL and p-GaN with high hole concentration for the efficient micro-LED emissive display are proposed. The sensitivity to defect density is also highlighted for micro-LED.

Surface integrity and machining accuracy have important effects on the fatigue life of blisk. During the electrochemical machining (ECM) of blisk, the blade is processed piece by piece. The machined blade profile is exposed to the electric field under low current density and is corroded when the next blade is processed. To investigate stray corrosion during the ECM of blisk, we analyzed the ηω–i curve of Inconel 718 and found that Inconel 718 continues to dissolve at very low current density. We then established a mathematical model of the stray corrosion of blisk in consideration of the electric field factor. Numerical simulations demonstrated that stray corrosion occurs during the ECM of blisk when the machining gap is large (> 1 mm). In a basic experimental investigation of the stray corrosion of Inconel 718, when the machining gap reached 40 mm, the machining time was 220 s, and the amount of corrosion was 0.033 mm. We also carried out ECM experiments with and without protecting the blade from attack by stray current using electrical insulation tape. The maximum corrosion amount of the machined blade was 0.035 mm without protection. In contrast, the protected machined blade was not corroded, and protection enhanced the accuracy and quality of the blisk blade ECM profile.

Jet electrochemical micromilling (JEMM) exhibits significant potential for high-efficiency and high-quality machining of titanium alloy microstructures. However, during the JEMM process, the machined surface of the workpiece inevitably experiences stray current attacks at low current levels. Due to the formation of a dense passive film on the surface of the titanium alloy under electrochemical action, stray corrosion occurs on the machined surface. Hence, the electrochemical dissolution behavior of titanium alloys at low current densities directly impacts both machining efficiency and quality. This study first analyzed the effects of electrolyte composition and current density on the transpassive potential, breakdown of the passive film, current efficiency, and the dissolved surface on Ti-6Al-4V. The transpassive potential and electrochemical impedance of Ti-6Al-4V were found to be lower in NaCl solution than in NaNO3 solution. In addition, lower current densities enabled higher current efficiency and resulted in a more uniform and flat dissolution surface. Subsequent experiments used these two solutions for JEMM of complex-shaped microstructures on Ti-6Al-4V. The findings demonstrated that, compared to the NaNO3 solution, the use of NaCl solution increases the material removal rate by approximately 30%, enhances the aspect ratio by about 26%, and reduces surface roughness by roughly 58%. This indicates that employing NaCl solution can lead to superior machining efficiency and quality.

Low-density polyethylene (LDPE) sheets (3.0 ± 0.1 cm) received sequential treatment, first by the action of direct-current low-pressure plasma (DC-LPP) with a 100% oxygen partial pressure, 3.0 × 10−2 mbar pressure, 600 V DC tension, 5.6 cm distance, 6-min treatment. Then, sheets were submitted to TiO2 photocatalysis at UV radiation at 254 nm (TiO2/UV) with a pH value of 4.5 ± 0.2 and a TiO2 concentration of 1 gL−1. We achieved a complementary effect on the transformation of LDPE films. With the first treatment, ablation was generated, which increased hydrophilicity. With the second treatment, the cavities appeared. The changes in the LDPE sheets’ hydrophobicity were measured using the static contact angle (SCA) technique. The photocatalytic degradation curve at 400 h revealed that the DC-LPP photocatalysis sequential process decreased SCA by 82°. This was achieved by the incorporation of polar groups, which increased hydrophilicity, roughness, and rigidity by 12 and 38%, respectively. These sequential processes could be employed for LDPE and other material biodegradation pretreatment.

To address the issue that current ripple in traditional switching power amplifiers (SPA) for active magnetic bearing (AMB) systems is constrained by the switching frequency, this paper proposes a novel LCL filter-based switching power amplifier (LCL-SPA) along with its parameter design and high-performance control strategy. Without altering the original full-bridge topology or the switching frequency, the proposed scheme achieves superior ripple suppression. To tackle the inherent resonance problem of the LCL filter, a sensorless capacitor current feedback active damping (CCFAD) strategy is proposed. This approach effectively suppresses resonance without additional hardware sensors and ensures system stability under digital control delays. Furthermore, to overcome the limitations of traditional PI controllers in terms of the dynamic performance and parameter tuning of the LCL-SPA, a high-performance LESO-based control algorithm within the Linear Active Disturbance Rejection Control (LADRC) framework is designed. By utilizing a Linear Extended State Observer (LESO) to estimate and compensate for total lumped disturbances in real-time, the algorithm simplifies the parameter tuning process and achieves rapid current tracking with nearly zero overshoot. Experimental results demonstrate that the proposed LCL-SPA achieves extremely low current ripple across various reference currents, with the ripple minimized to 20 mA at a 3 A load. Frequency response tests confirm that the system possesses a closed-loop bandwidth of up to 2 kHz, satisfying the high dynamic requirements of magnetic bearings.

Electrochemical reduction is currently one of promising methods for nitrate removal from water, yet most treatment approaches have problems of high cost and energy consumption. In this work, a low current density was applied in electrochemical reduction of nitrate. Copper-modified titanium (Cu/Ti) electrodes with optimal electrochemical activity and fastest kinetics were firstly screened. Thirty minutes of electrodeposition time and neutral pH were found to have the greatest nitrate reduction rate of 83.14%. To further improve the removal of nitrate, activated carbon (AC) and copper-modified activated carbon (Cu/AC) particles were applied to construct three-dimensional reaction systems, with removal rates of nitrate of 88.72% and 96.05%, respectively. The average conversion rates of nitrate to ammonia nitrogen increased from 15.28% to 42.68% and 62.64% in AC- and Cu/AC-based reaction systems, respectively. Oxidation of Cu(0) on surfaces of Cu/Ti cathode and Cu/AC particles to Cu(I) was revealed by X-ray photoelectron spectroscopy (XPS) and Cu LMM spectra analysis. Besides, results of water chemistry characteristics indicated the conversion of AC to carbonate ion. It could be concluded that enhanced nitrate reduction of Cu/Ti-based reaction system was attributed by Cu particle- and AC-mediated electron transfer. This study provided a reference for low-cost electrochemical reduction of nitrate.

An easily extensible interleaved high-voltage gain boost converter is proposed in this paper, which can be applied to electric vehicles, photovoltaic power generation and other fields. The proposed converter is expandable with different voltage multiplication cells according to different gain requirements. The low voltage side of the proposed converter is interleaved with two inductors, and the high voltage side is structured with multiple capacitors in series. The proposed converter has the advantages of low voltage stress for the whole devices, low input current ripple, inductor currents self-averaging, capacitor voltages self-balancing, simple control, and easy extension. First, the structure and principles of the proposed converter are introduced and analyzed. Then the performance of the converter in various aspects is theoretically analyzed and compared with existing converters. Next, the double closed-loop control system is designed. Finally, an experimental prototype with an input of 24 V, an output of 400 V and a rated power of 180 W is built and implemented, and the superior performance of proposed converter is experimentally verified.

A precision resistance measurement method based on synchronous sampling is proposed to enable accurate resistance measurement under low-current testing conditions. This method utilizes a single current source input, connecting the standard resistor and the test resistor in series. The setup is simple, easy to operate, and allows for the convenient and rapid comparison of the voltage across the resistors. The resistance value of the test resistor is determined through calculation, achieving high measurement accuracy. An experimental comparison of two standard resistors under a low current of 1 μA demonstrated that the data dispersion reached the 10−6 level, and the measurement error was within the 10−6 range. This study also employed a resistance ratio measurement method based on room-temperature Direct Current Comparator (DCC) technology to validate the superiority of the proposed synchronous sampling approach under low-current measurement conditions. The comparative analysis demonstrated that our method exhibits significant advantages over conventional DCC techniques under a low current of 1 μA. This paper presents the first demonstration of high-accuracy resistance ratio measurement using synchronous sampling under weak current conditions. Experimental results verify that at 1 μA current level, the proposed method achieves superior measurement accuracy and lower uncertainty compared to conventional precision DC current comparator techniques under identical test conditions.

In this paper, a new single-stage single-switch, flyback-forward based and isolated power factor correction (PFC) converter is proposed. The proposed converter provides high power factor (PF), low current stress, high efficiency, low cost, and tight output voltage regulation. Flyback and forward converters operate in discontinuous current mode (DCM) simultaneously. The flyback converter operates at full power, uses the leakage inductance and provides high PF, transfers most of the power to the output storage capacitor, and transfers the remaining power to the input storage capacitor. The forward converter is supplied by the input storage capacitor, operates with low power, transfers all power to the output, and also provides output regulation. Thus, high PF, near direct power transfer (NDPT), low current stress on the power switch, high efficiency and low cost are achieved. A detailed theoretical analysis of the proposed converter is carried out and is verified with an experimental prototype with 220V AC input voltage, 120V DC output voltage, 120 W output power, and 100 kHz switching frequency. In the converter, the peak current of the switch is decreased from 8.75 A to 5.5 A and the total efficiency is increased from 74 to 85% compared to the equivalent converter without NDPT at full power.

Perovskite light-emitting diodes (LEDs) have attracted broad attention due to their rapidly increasing external quantum efficiencies (EQEs) 1 – 15 . However, most high EQEs of perovskite LEDs are reported at low current densities (<1 mA cm −2 ) and low brightness. Decrease in efficiency and rapid degradation at high brightness inhibit their practical applications. Here, we demonstrate perovskite LEDs with exceptional performance at high brightness, achieved by the introduction of a multifunctional molecule that simultaneously removes non-radiative regions in the perovskite films and suppresses luminescence quenching of perovskites at the interface with charge-transport layers. The resulting LEDs emit near-infrared light at 800 nm, show a peak EQE of 23.8% at 33 mA cm −2 and retain EQEs more than 10% at high current densities of up to 1,000 mA cm −2 . In pulsed operation, they retain EQE of 16% at an ultrahigh current density of 4,000 mA cm −2 , along with a high radiance of more than 3,200 W s −1  m −2 . Notably, an operational half-lifetime of 32 h at an initial radiance of 107 W s −1  m −2 has been achieved, representing the best stability for perovskite LEDs having EQEs exceeding 20% at high brightness levels. The demonstration of efficient and stable perovskite LEDs at high brightness is an important step towards commercialization and opens up new opportunities beyond conventional LED technologies, such as perovskite electrically pumped lasers. Perovskite LEDs with exceptional performance at high brightness are demonstrated achieving an operational half-lifetime of 32 hours, an important step towards commercialization opening up new opportunities beyond conventional LED technologies, such as perovskite electrically pumped lasers.