Confining amphiprotic proton sources within the framework of crystalline materials is recognized as an effective strategy for improving their proton conductivities. Two new compounds ([(TPA)(AlMo6O24)]·3H2O, named as CUST-841 and [Zn2(HSO4)2(TPA)2(AlMo6O24)]·5H2O, named as CUST-842) have been successfully synthesized under hydrothermal conditions. Thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD) results demonstrated that both compounds exhibit excellent water and thermal stabilities. Alternating current (AC) impedance spectroscopy revealed that CUST-842 achieved a maximum proton conductivity of 6.05 × 10-4 S cm-1, which is an order of magnitude higher than that of CUST-841 under conditions of 95 °C and 98% relative humidity (RH). Comparative analysis between CUST-842 and CUST-841 demonstrates a synergistic effect of Zn2+ coordination and HSO4- incorporation in the construction of continuous hydrogen-bond networks and the promotion of proton dissociation. The amphiprotic HSO4- in CUST-842 acts as "dissociation enhancers" to facilitate efficient proton dissociation, while the abundant N-sites within the nanopores and Zn2+-coordinated water molecules strengthen the hydrogen-bond network for rapid proton diffusion, as confirmed by 1H solid-state nuclear magnetic resonance (NMR) spectroscopy. This study provides insights into the synthesis of polyoxometalate (POM)-based solid proton conductors.

ABSTRACT This study investigates the impact of alternating current (AC) and pulsed current (PC) on gas tungsten arc welding (GTAW) of AZ31 Mg alloy sheets. Welding was performed using AC (85, 125 A) and PC (130–90 P, 140–100 P) conditions. Results indicated that the welding current mode influences grain morphology and mechanical performance. High-heat input (125 A, 140–100 P) led to grain coarsening; however, the 130–90 P condition resulted in refined equiaxed grains, reducing the average grain size by ∼35–40%. The 125 A joint achieved the highest tensile strength (225 MPa), while the 130–90 P joint provided nearly equivalent strength at a reduced heat input compared with the 125 A condition. The hardness profiles indicated that the base-metal consistently demonstrated greater hardness compared to the heat-affected zone. The weld metal exhibited the lowest hardness values, indicating the influence of thermal softening and microstructural recovery in the welded regions. The findings suggest that optimised pulsed current GTAW achieves a balance between mechanical performance and microstructural control while requiring a reduced heat input for AZ31 Mg alloy welds.

Abstract Ionic wind thrusters are emerging electrohydrodynamic propulsion devices that have drawn significant interest owing to their simple structure, silent operation, and potential applications in microaerial vehicles. A high-voltage electrode is a crucial component that directly impacts the corona discharge efficiency and the resultant ionic wind thrust. In this study, significant mechanical vibrations were observed in a high-voltage tungsten wire electrode under alternating current (AC) excitation in a wire-to-cylinder ionic wind thruster operating under atmospheric conditions. The experiments were conducted at a fixed AC frequency of 10 kHz, with voltages ranging from 5 kV to 9 kV. The electrode vibrations were measured using a 3D high-speed video extensometer, and the waveforms and frequency spectra were analyzed. The results reveal that the vibration amplitude increases significantly with voltage. The spectrum reveals harmonic responses at 120 Hz and its multiples (240 Hz and 360 Hz), indicating strong nonlinear vibration behavior. The periodic Coulomb force induced by the AC electric field was confirmed to be the primary excitation source.

Experimental and numerical investigations of the alternating current (AC) susceptibility, examined multigrain La0.66Sr0.34MnO3 (LSMO) thin films (thickness d = 250 nm) grown by radio-frequency (RF) magnetron sputtering on lattice-mismatched yttria-stabilized zirconia YSZ(001) substrates. The films exhibit a columnar structure comprising two types of grains, with (001)- and (011)-oriented planes of a pseudocubic lattice aligned parallel to the film surface. Field- and angle-dependent AC susceptibility measurements at 78 K reveal characteristic peak- and tip-like anomalies, attributed to contributions from grains with three distinct directions of easy magnetization axes within the film plane. Numerical modeling based on the transverse susceptibility theory for single-domain ferromagnetic grains, incorporating first- and second-order anisotropy constants, corroborates the experimental findings and elucidates the role of different grain types in magnetization switching and AC susceptibility response. This study provides a quantitative determination of the three in-plane easy magnetization axes in LSMO/YSZ(001) films and clarifies their influence on the magnetization dynamics of multigrain thin films. The demonstrated control over multigrain LSMO/YSZ(001) thin films with distinct in-plane easy magnetization axes and well-characterized AC susceptibility suggests potential applications in magnetic memory, spintronic devices, and precision magnetic sensing.

ABSTRACT Phase‐locked loops (PLLs) are critical for synchronizing modular multilevel converter high voltage direct current (MMC‐HVDC) systems with alternating current (AC) grids, yet their stability impacts remain underexplored. This study systematically compares the impacts of the synchronous reference frame‐PLL (SRF‐PLL) and the inertia PLL (IPLL) on small‐signal stability and large‐signal synchronization. A unified framework is adopted to enable unbiased comparison by aligning their bandwidths. A small‐signal model, incorporating PLL dynamics, is developed, based on which PLL impacts are examined using impedance‐based generalized Nyquist criteria. The analysis results show that system stability depends primarily on PLL bandwidth rather than structure. This reveals inherent limitations of PLL‐based synchronization and motivates PLL‐less designs for improving stability. To enhance large‐signal synchronization, a phase correction pathway is introduced for the SRF‐PLL. This approach improves synchronization while avoiding steady‐state phase detection errors inherent to the IPLL. Finally, all results are verified by non‐linear time‐domain electromagnetic transient simulations in PSCAD. This work advances quantitative understanding of PLL characteristics and stability impacts in MMC‐HVDC systems, providing motivation for adopting PLL‐less system designs.

Electric Vehicle (EV) inverters are essential components in the powertrain of electric vehicles, converting direct current (DC) from the battery into alternating current (AC) to power the electric motor. The seals within EV inverters are critical for maintaining system integrity, preventing contamination, and ensuring the proper functioning of inverter components. This study focuses on the performance of High Voltage Direct Current (HVDC) Press-In-Place (PIP) seals made from Ethylene Propylene Diene Monomer (EPDM) rubber, a Hyperelastic material known for its large elastic deformation and incompressibility. The research investigates the mechanical performance of EPDM PIP seals for three material conditions: Least Material Condition (LMC), Nominal Material Condition (NMC) & Maximum Material Condition (MMC). The EPDM PIP seals were evaluated at different temperatures up to 1000hrs and under Thermal Cyclic loading. A combined simulation approach incorporating the Mullins effect and viscoelastic relaxation was adapted to model stress softening over multiple thermal cycles and up to a large duration of 1000hrs. Results indicate that the PIP (Press-in-place) seals lose contact pressure during thermal cycling due to Stress Relaxation & Mullin’s effect occurring due to expansion & contraction of seals inducing cyclic Thermal strains. The results also reveal significant stress-softening in early cycles due to change in polymer chain structure, followed by gradual stabilization. Viscoelastic effects contribute to stress decay during hold periods, impacting long-term sealing performance. The study provides insights into the interplay between material behaviour and thermal loading offering design direction for improving seal reliability in EV inverter systems.

Alternating current (AC) has recently been explored as a powerful electrolysis operating mode to access synthetic intermediates, avoiding overoxidation events and electrode passivation. In this work, we explore the applications of AC to the electrooxidative nitroso Diels-Alder reaction (nDA) through the in situ formation of acyl nitroso intermediates (dienophile). Further reaction with 1,2-dihydropyridine (DHP) derivatives (dienes) unlocked a sustainable regio- and stereoselective protocol for the synthesis of oxadiazo[2.2.2]octenes.

This paper presents the modification and experimental validation of a mathematical model for a single junction thermal voltage converter (SJTC) designed for high-precision alternating current (AC) voltage transfer. The original model is severely constrained by two main issues: (1) computational instability above 50 MHz due to the limitations of the housing impedance approximation, and (2) insufficient accuracy above 1 MHz due to the neglect of high-frequency skin effect and magnetic core effects in the Dumet wire leads. Significant refinements are subsequently implemented to extend the calculable frequency range of the standard from 1 to 100 MHz. This required re-evaluation of the Dumet wire leads’ frequency-dependent resistance and inductance using finite element method (FEM) simulations, which accounted for the skin effect and the magnetic permeability of the FeNi42 core. Additionally, the housing impedance calculation is stabilized using a formulation based on scaled modified Bessel functions, and the electrical conductivity of the input N-type connector pin is explicitly modeled. The improved model is validated against a reference calorimetric thermal voltage converter (CTVC) using 3 and 5 V nominal voltage standards. The results indicated excellent agreement between the calculated and measured AC-direct current (DC) transfer differences up to 10 MHz. In the extended frequency regime, the model correctly predicted the transition to negative transfer differences observed above 2 MHz for the 5 V standard. The largest discrepancies between the measured and calculated values occurred at 100 MHz. The measured transfer difference reached −15,090 (µV/V) with an expanded uncertainty (k = 2) of 190 (µV/V), whereas the calculated value is −12,500 (µV/V) with an expanded uncertainty of 3900 (µV/V). Although the deviation between the model and measurement increased above 30 MHz, the results remained consistent within the expanded measurement uncertainties across the entire 10 kHz to 100 MHz range, demonstrating the model’s suitability for providing traceability in high-frequency voltage metrology.

Background: Bone fracture is a partial or complete break in the continuity of a bone, which poses a significant healthcare burden. It is important to discover a novel method to stimulate and speed-up the healing of bone fractures. Aim: This study aimed to investigate the effects and mechanisms of alternating current (AC) in promoting bone fracture healing. Methods: A rabbit bone fracture model was used. X-ray and Micro-CT evaluated fracture healing, while HE staining and immunohistochemistry assessed morphological changes. In vitro, pre-osteoblastic cells were tested with alizarin red S staining and alkaline phosphatase (ALP) activity. RNA-seq analysis explored potential mechanisms. Results: X-ray evaluation showed that alternating current stimulation (ACS) promoted bone formation and shaping by day 14 post-treatment. Micro-CT results revealed significant new bone formation as early as day 3 and day 7 (p < 0.05). HE staining indicated more trabecular bone formation in the ACS group compared to the model group at days 7 and 14. Immunohistochemistry showed higher expression of BMP-2 and VEGF in the ACS group by day 7. In vitro, ACS enhanced osteogenic differentiation, increasing calcified nodule formation and ALP activity. Gene expression analysis demonstrated significant changes in key osteogenic genes, confirmed by multiple immunohistochemical staining. Conclusions: ACS may be a novel method for treating bone fractures more rapidly, significantly relieving the patient’s burden, particularly in the early stages of bone healing.

The diagenetic pathways, mineral types, and products of magnetic minerals in gas hydrate-bearing sediments are closely linked to burial depth. During IODP Expedition 375, drilling at the northern Hikurangi margin recovered 83.09 m of core from the gas hydrate stability zone (518.4–640.0 m depth) at Site U1519C. This provides an exceptional opportunity to investigate progressive diagenesis and fluid-driven late-stage diagenesis in deeply buried gas hydrate-bearing sediments. We conducted low-temperature magnetic measurements on 13 samples from this interval, including: (i) Low-temperature cycling (LTC) cycles, (ii) Zero-field-cooled (ZFC) and field-cooled (FC) curves, (iii) Low-temperature hysteresis loops, and (iv) Low-temperature alternating current (AC) magnetic susceptibility. Using features such as low-temperature transitions and curve trajectory patterns, we determined the types, concentrations, and assemblages of magnetic minerals, analyzed the origins of magnetic particles. Key results reveal: (1) Deeply buried sediments exhibit notably low SIRM intensity, indicating scarce magnetic minerals dominated by superparamagnetic (SP) and single-domain (SD) particles. This indicates that the deeply buried sediments experienced extensive pyritization under sustained reducing diagenetic conditions; (2)Despite the dominance of SP signals in the low-temperature FC/ZFC curves, the observation of the Verwey transition at ∼118 K—a characteristic low-temperature phase transition stemming from magnetite’s structural transformation—provides definitive evidence for the presence of trace magnetite even at such depths (&amp;gt;580 mbsf); (3) A double Verwey transition (∼106 K and ∼118 K) was observed in some samples, which indicates the coexistence of biogenic magnetite and nearly stoichiometric magnetite; (4) Authigenic Greigite (Fe 3 S 4 ), an intermediate product of pyritization (FeS 2 ), is detected. Some greigite likely exists as SP particles, while a low index of hysteresis parameters (D JH ) indicates limited contributions from stable SD greigite among ferrimagnetic minerals.This study provides low-temperature magnetic evidence for diagenetic processes affecting magnetic minerals in deeply buried gas hydrate-bearing sediments. It reveals partial magnetite preservation, greigite formation and transformation, and ultimate pyritization, offering new insights into magnetic mineral evolution in such environments.

Abstract To realize the free falling test mass in gravitational wave detection in space, an alternative current (AC) electrostatic control strategy is proposed and developed. It is significant to test and verify the AC control actuation scheme on the ground. In this paper, a two-stage torsion pendulum is used to test the performance of the AC control actuator of inertial sensor for Tianqin project. First, the pendulum facility combined with a test mass, a capacitive position sensor and an AC control actuator is constructed. Experimental results show that the sensitivities of the pendulum achieve 10 -11 N/Hz 1/2 and 10 -13 Nm/Hz 1/2 , respectively, and the pendulum provides a chance to realize the performance test of two degree-of-freedom sensitivities of the actuator, experimental verification of AC control strategy and so on, which is first reported to test performance of the AC control actuator of a space inertial sensor on the ground.

Abstract Precise control of microscale object rotation is essential for numerous biomedical and microelectromechanical applications. For example, somatic cell nuclear transfer for aquatic biomedical models such as zebrafish faces significant technical challenges, particularly in egg trapping and alignment of an injection needle with the micropyle. In this study, we developed a 3D resin-printed microdevice to achieve frequency-selective electrorotation of dielectric microspheres using a quadrupole electrode configuration driven by phase-shifted alternating current (AC). Theoretical analysis based on the Clausius–Mossotti factor, which governs the polarization of a particle concerning its surrounding environment, highlights the critical role of its imaginary component in the induced dipole moment from the AC field that generates torque. Simulations conducted in COMSOL Multiphysics confirmed the formation of symmetric torque-driven rotation without significant micro-scale object translation. The frequency response of angular velocity exhibited a unimodal profile, with a peak near 4 MHz corresponding to maximum torque efficiency. Experimental validation using 700 µ m polystyrene microspheres in Dulbecco’s Phosphate Buffered Saline demonstrated consistent clockwise rotation, with a peak angular velocity of 8.1° s −1 observed at 900 kHz and 16 Vp–p. Although the experimental peak angular velocity occurred at a lower frequency than the theoretical maximum, the rotational trend followed the polarization relaxation behavior captured by Im[ K cm ]. Parameter studies further revealed that increasing microscale object permittivity amplified torque generation, while higher medium permittivity reduced it, underscoring the tunability of electrorotation via dielectric properties. This work demonstrates a robust and scalable platform for manipulating large microscale objects. It lays the foundation for future applications involving biologically relevant objects, such as eggs of biomedical research models.

Herein, we report the first miniaturized, wireless electrochemical flow reactor capable of performing both reactant pumping and asymmetric synthesis within a single, integrated device. The reactor consists of a hollow, conductive polymer tube where the outer polypyrrole (Ppy) shell acts as an electromechanical pump, and the inner layer, constituted of a chiral thiophene-based oligomer, serves as the enantioselective catalyst. This integrated design overcomes mass-transport limitations and eliminates the need for external pumps. By employing an alternating current (AC) protocol, we achieve near-quantitative yield (99%) and exceptional enantioselectivity (>99% ee) for the reduction of acetophenone. The system's utility is showcased across three mechanistically distinct transformations, ketone reduction, sulfide oxidation, and reductive amination, culminating in the direct asymmetric synthesis of Ugi's amine, the chiral probe used in our mechanistic studies, with high stereocontrol (>99.5% ee). This work introduces a new paradigm for reagent-free, pump-free asymmetric synthesis and provides a validated, predictive model for the rational design of smart, automated chemical manufacturing platforms.

Oxygen vacancies play a crucial role in controlling the physical properties of complex oxides. In La0.7Sr0.3MnO3-δ, the topotactic phase transition from Perovskite (PV) to Brownmillerite (BM) can be triggered, e.g., via oxygen removal during thermal annealing. Here, a very efficient thermal vacuum annealing method is reported using aluminum as an oxygen getter material. The topotactic phase transition is characterized by X-ray Diffraction, which confirms a successful transition from PV to BM in La0.7Sr0.3MnO3-δ thin films grown via physical vapor deposition. The efficiency of this method is confirmed using La0.7Sr0.3MnO3-δ micron-sized bulk powder. The accompanying transition from the original Ferromagnetic (FM) to an Antiferromagnetic (AF) state and the simultaneous transition from a metallic to an insulating state are characterized using Superconducting Quantum Interference Device (SQUID) magnetometry and Alternating Current (AC) resistivity measurements, respectively. The near-surface manganese oxidation states are probed by synchrotron X-ray Absorption Spectroscopy. Moreover, X-ray Reflectivity, Atomic Force Microscopy, and Scanning Transmission Electron Microscopy reveal surface segregation and cation redistribution during the oxygen getter-assisted annealing process.

HighlightsWhat are the main findings?AC frequency significantly affected MAO coating morphology and thickness.CaPSe_100 coating showed the most uniform structure and highest porosity (28.4%).All coatings were strongly hydrophilic (contact angles 8–18°).CaPSe_100 achieved a degradation rate of ~0.012 mm/year vs. ~5.50 mm/year for bare Mg.What are the implications of the main findings?Frequency tuning enables control of MgO growth and coating uniformity.The MAO coating effectively suppresses hydrogen evolution on pure Mg.Porous and hydrophilic surfaces may enhance osseointegration potential.Findings support the design of durable, multifunctional coatings for Mg implants.The present study investigates the influence of alternating current (AC) frequency on the formation and properties of calcium-, phosphorus-, and selenium-containing micro-arc oxidation (MAO) coatings on high-purity magnesium. Coatings were produced at 50–400 Hz in a phytic-acid-based electrolyte containing Ca, P, and Se precursors, and their structure, chemistry, and functional performance were systematically evaluated. Surface morphology, analyzed by SEM and optical profilometry, revealed frequency-dependent features: lower frequencies (50 Hz) promoted thicker, rougher coatings with extensive cracking, whereas intermediate frequencies (100–200 Hz) yielded more uniform, porous surfaces. The CaPSe_100 specimen exhibited the most homogeneous topography (lowest S10z and SD) combined with the highest porosity (28.4%), strong hydrophilicity, and the greatest selenium incorporation (1.30 wt.%). Hydrogen evolution testing in Hanks’ solution demonstrated a drastic improvement in corrosion resistance following MAO treatment: the degradation rate of bare Mg (5.50 mm/year) was reduced to 0.012 mm/year for the CaPSe_100 coating—well below the clinical tolerance threshold for biodegradable implants. This outstanding performance is attributed to the synergistic effect of a uniform oxide barrier, optimized porosity, and homogeneous surface morphology. The results highlight the potential of frequency-controlled AC-MAO processing as a route to tailor magnesium surfaces for multifunctional, corrosion-resistant biomedical applications.

RNA biomarkers are vital for diagnosing infections, cancer, and neurodegenerative diseases. RT-qPCR is sensitive but complex and equipment-intensive, limiting point-of-care use. Herein, for the first time, an organic electrochemical transistor (OECT) biosensor is reported utilizing small molecules as recognition elements for rapid, ultrasensitive and amplification-free detection of RNA. The biosensor leverages "click chemistry" to precisely immobilize screened and chemically edited small molecules to the OECT gate, enabling efficient target RNA binding. To further enhance sensitivity and reduce detection time, a rapid sample incubation module utilizing alternating current (AC) electrokinetic acceleration without the influence of electric currents and thermal effects strategy is employed to accelerate biomolecule transport and increase binding kinetics. This approach is validated using a model system incorporating C5, a chemically optimized small-molecule ligand that selectively binds SARS-CoV-2 RNA. The resulting biosensor achieves real-time, amplification-free RNA detection within three minutes, and the results are transmitted to electronic devices via Bluetooth. Notably, it shows impressive sensitivity (0.3 aM) and excellent long-term stability, retaining functional sensitivity for five months under ambient storage. This work establishes a new paradigm for RNA biosensing, demonstrating the power of integrating small-molecule recognition, electrochemical transduction and AC field enhancement for next-generation rapid diagnostics.

Infrared thermography (IRT) is a widely used non-contact technique for quantifying thermal performance in industrial heating systems. This study employs IRT to analyze and compare the thermal behavior and electrical power efficiency of a heating resistor within a distillation column boiler under alternating current (AC) and direct current (DC) power supply. Experiments were conducted using a distillation pilot plant, which included a 130 W heating resistor powered by an AC (60 Hz) source and an equivalent DC source considering different voltage-current configurations. Thermal dynamics were captured using a calibrated mid-wave IR camera (7.5 to 13 µm spectral range), in parallel with electrical power measurements from a data-acquisition card embedded system. The proposed methodology establishes an IRT protocol for quantifying thermal responses via IRT images, allowing for mapping 2D temperature heterogeneity through emissivity-corrected thermograms. Power efficiency analyses showed DC reduced Joule losses while AC exhibited superior thermal stability during prolonged operation. This IRT-integrated approach provides actionable insights for optimizing distillation energy systems and aligns with industrial electrification initiatives. The protocol is scalable for infrared-based monitoring of thermo-electric processes in chemical, pharmaceutical, and renewable energy applications.

In this study, new polymethyl methacrylate (PMMA) composites were developed by doping with tin oxide (SnO2) nanoparticles at varying concentrations (2%, 5%, 10%, and 20% by weight) via solution casting. The dielectric properties and alternating current (AC) conductivity of SnO2/PMMA were examined. The impact of SnO2 ratio, frequency and temperatures on the electrical properties were investigated. Unlike previous studies with limited conditions, our work systematically explores a broad frequency–temperature range, revealing deeper insights into interfacial polarization and charge transport. Results showed that the doping with SnO2 nanoparticles significantly enhanced the dielectric constant (ε′), particularly at lower frequencies, due to increased interfacial polarization (Maxwell-Wagner-Sillars effect). The dielectric loss (ε″) also increased with SnO2 content and temperature, reflecting enhanced interfacial polarization and restricted polymer chain mobility. The AC conductivity followed a power-law dependence on frequency, indicating charge hopping mechanisms, with higher conductivities observed in SnO2-doped PMMA. The real and imaginary parts of the electric modulus (M’ and M″) increased with nanoparticle content, suggesting improved dielectric relaxation. These results demonstrate that SnO2 nanoparticles effectively enhance the dielectric and conductive properties of PMMA, making these composites suitable for advanced electronic applications.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-30922-5.

Abstract In high-power three-level converters, busbar stray inductance critically influences switching transient and thermal distribution. This paper establishes a parametric stray inductance model for laminated busbars and analyzes its impact on commutation paths. To resolve thermal imbalance, a power loss thermal balance method optimizes control strategies, enabling stable commutation path switching and preventing system instability at switching points. The key is to propose weighting factors based on stray parameters for dynamic energy exchange among internal, external, and clamp switches, combined with case temperature-dependent modulation to achieve thermal balance in three-level converters. The accuracy of the model established and the feasibility of the adopted approach are verified by simulation studies in MATLAB/Simulink and experiments based on a 900 V Alternating Current (AC) power system.

The electro-coalescence, which is a phenomenon of coalescence in the presence of electric field of two equal-sized droplets with constant surface tension at the droplet and medium interface, has been investigated based on the phase-field model to track the evolution of the droplet interfaces. The coalescence efficiency has been quantified by analyzing the growth rate of the bridge radius after the droplet tips merge, as well as the total coalescence time, defined as the sum of the approach and fusion times. The results demonstrate that the coalescence efficiency highly depends on the type of electric field applied. In this study, the behavior of coalescence under direct current (DC) and alternating current (AC) fields for high capillary numbers has been explored. Furthermore, the restoration of the spherical droplet shape under AC and DC fields at high capillary numbers has been examined. The coalescence characteristics of various waveforms with the same root-mean-square electric field strength, including AC, half-cosine, and DC square waves, at both low and high frequencies have been compared. Special emphasis has been placed on analyzing how the frequency affects electro-coalescence and the sensitivity of the coalescence happens time to frequency variations for time-periodic electric fields.