Hasil untuk "Electricity and magnetism"

Mariajose Giraldo-Jaramillo, Carolina Tranchita

The progressive replacement of synchronous machines by inverter-based resources (IBRs) reduces system inertia and short-circuit strength, making power systems more vulnerable to frequency and voltage instabilities. Grid-forming (GFM) inverters can mitigate these issues by establishing voltage and frequency references, emulating inertia and enabling autonomous operation during islanding, while grid-following (GFL) inverters mainly contribute to reactive power support. This paper evaluates the capability of GFM inverters to provide grid support under both grid-connected and islanded conditions at the distribution level. Electromagnetic transient (EMT) simulations in MATLAB/Simulink R2022b were performed on a 20 kV radial microgrid comprising GFM and GFL inverters and aggregated load. Small disturbances, including phase-angle jumps and voltage steps at the point of common coupling, were introduced while varying the GFM share and virtual inertia constants. Also, local variables were assessed during islanded operation and separation process. Results indicate that maintaining a GFM share above approximately 30–40% with inertia constants exceeding 2 s significantly enhances frequency stability, supports successful transitions to islanded operation, and improves overall resilience. The study highlights the complementary roles of GFM and GFL in enabling the stable and resilient operation of converter-dominated distribution systems.

Bangdou Huang, Chenhua Ren, Cheng Zhang et al.

ABSTRACT Anomalous‐energy runaway electrons (RAEs), whose energy exceeds the maximum potential difference across the discharge gap, are widely observed in various plasma phenomena. This study investigates the origination of anomalous‐energy RAEs in fast ionisation waves (FIWs) formed during pulsed gas breakdown. Synchronised observation of RAEs and their induced bremsstrahlung X‐ray at different locations of the FIW is performed, which is combined with measurement of spatial‐temporal evolution of FIW potential. It is revealed that anomalous‐energy RAEs, preceding regular RAEs, have an ultrashort beam with a picosecond pulse width, and RAEs tend to maintain their energy during FIW propagation before being deposited into the anode. Particle‐in‐cell Monte Carlo collision (PIC‐MCC) simulation illustrates that the ‘pace‐matching’ between initial electron acceleration through cathode potential drop and potential lift‐up during FIW inception opens a narrow window for forming anomalous‐energy RAEs.

Alex J. Vernon

In nonparaxial, monochromatic light the electric and magnetic fields generally have different energy densities, different singularities and different polarisation structures. A topological picture of the electric field or magnetic field in isolation cannot capture the elusive topology of nonparaxial light that exists in the spatially dependent relationship between the two fields: the degree to which light breaks fundamental symmetries (parity, duality, time-reversal). With this work a new ellipse is introduced that resides not in real space, but in electric-magnetic (EM) space, and whose geometry depends on these broken symmetries. The EM ellipse has circular and linear polarisation singularities and may be organised into particle-like textures. These thus-far hidden topologies are present even in rudimentary structured waves, for a second-order EM-space meron is shown to be present in a focussed linearly polarised vortex beam.

Juan Casanova-Chafer, Pedro Atienzar, Carla Bittencourt

Theoretical studies have indicated that borophene is a promising two-dimensional material characterized by remarkable chemical, mechanical, and electrical properties. Nonetheless, its practical applications in areas such as catalysis and gas sensing are hindered by the limited density of reactive sites in its pristine form. To address this limitation, the present study explores the controlled fluorination of borophene nanoflakes as a strategy to modify their surface chemistry and enhance the availability of active sites. Furthermore, it is anticipated that surface fluorination will improve hydrophobicity, which is crucial for reducing humidity-related interference in sensing applications. In this study, we report the successful functionalization of borophene nanoflakes with fluorine using a plasma arc discharge technique for the first time. Borophene nanolayers were synthesized via a sonochemical-assisted exfoliation method, yielding nanosheets with an average lateral dimension of approximately 100 nm. The fluorinated samples were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). A systematic investigation of plasma exposure durations demonstrated that fluorine was effectively introduced as a dopant while maintaining the crystallinity of the borophene lattice.

Qian Chen, You-Feng Cheng, Qi-Hang Peng et al.

This paper proposes a printed ridge gap waveguide (PRGW)-based 2 × 2 millimeter-wave antenna array with broad bandwidth and compact aperture. A dual-resonance element consisting of a quarter circular and a quarter annular patch is initially designed. Subsequently, to reduce the cross polarization (XP) radiation and enhance the gain of the proposed antenna, a four-element array with symmetric arrangement is developed, leading to a decline in the normalized XP levels from −4.5 to −18.9 dB and from −4.4 to −18.7 dB in the xoz and yoz planes, respectively. In addition, a pair of parasitic shorted half-circular patches is loaded to improve the antenna gain in the high-frequency range. Finally, a PRGW feeding network is designed and applied to provide differential feeding for the planar array. To validate the reflection and radiation performance, an array prototype is fabricated, and experimental verification is conducted. Measurement results show that a −10-dB impedance bandwidth of 14.3% (26.0–30.0 GHz) is realized for the prototype, and an average realized gain of 9.8 dBi with low XP radiation is achieved by the proposed array.

Chong SHAO, Rongyi HU, Jiao YU et al.

Energy storage is one of the important methods for mitigating the fluctuation of renewable energy. A refined simulation model is presented that can describe the material transport and energy conversion in a proton exchange membrane electrolyser (PEM). The model is constructed based on the component structure of the PEM, as well as the principles of electrochemistry and thermal equilibrium, taking into account the phenomenon of internal gas transport across the membrane. Based on this model, an electricity-hydrogen coupling system including electrochemical energy storage and hydrogen energy storage is established. A two-layer coordinated control strategy considering the charge state of electrochemical energy storage and the hydrogen state of hydrogen energy storage is proposed. The upper-layer power allocation considers the changes in electric and hydrogen load demands in the system, and uses the battery state of charge and hydrogen storage tank state of hydrogen as important constraints to determine the operating modes for each device in the system. The bottom layer control achieves power tracking adjustment by utilizing PQ control, VQ control, and other methods according to equipment operating characteristics. The effectiveness of this proposed model and control method is verified through simulations under several different operation scenarios. The research results can provide support for the optimization of control strategies for wind-photovoltaic-hydrogen storage systems.

Fatema Al-Salmani, Jordan Johnson, B. Thacker

We present an analysis of students' thinking skills as evidenced by free-response exam problems during the Covid-19 pandemic. We compare two inquiry-based, laboratory-based classical mechanics courses, one taught online and one taught in person during the pandemic, and two inquiry-based, laboratory-based electricity and magnetism courses, one taught online and the other in person during the pandemic. We use a rubric that was previously developed based on Bloom's taxonomy (revised version) to compare the thinking skills of students in classes taught by different pedagogies. We discuss the method and analysis, and present results and interpretations. No significant differences were found in thinking skills between students in the online and in-person pandemic classical mechanics courses. However, we did see a difference in the thinking skills between the online and in-person pandemic electricity and magnetism courses as the semester progressed.

Gabriele Riva, James Chongco, Jezreel Joy Paguio et al.

Amid the shift to online learning during the COVID-19 outbreak, the academic performance of students has become a concern. To address this, Adaptive Learning Systems (ALS) have emerged, these help in assessing students and delivering personalized content. This study develops an ALS incorporating K-means Clustering, Decision Tree, and Bayesian Network techniques, based on the Felder-Silverman Learning Style Model (FSLSM). The aim is to optimize learning materials based on students' current Knowledge Level (KL) and their Learning Style (LS). The students who utilized the proposed system showed substantial improvements in their performance across the Electromagnetic Spectrum, Light, Electricity, and Magnetism modules, with increases of 28.8%, 41.4%, 31.9%, and 32.9%, respectively. These findings provide strong evidence that the adaptive e-learning system had a significant positive impact on post-test scores compared to pre-test scores, surpassing the outcomes achieved with the traditional learning approach. With a silhouette score of 0.7 for K-Means clustering, an accuracy of 87.5% for Decision Tree, and a 95.1% acceptance value for the distribution of learning objects using the Bayesian Network, the proposed adaptive system demonstrated successful implementation of these machine learning algorithms. Furthermore, the proposed system received "excellent" ratings for functional stability, performance efficiency, compatibility, and reliability, with mean values of 4.49, 4.43, 4.43, 4.8, and 4.47 respectively.

Andrew M. Ritzmann, Michael D. LaCount, Michel Sassi et al.

In the event of a nuclear accident, fission products may be released into the environment. The release of 131I is of particular concern to human health. Iodine can be captured using a number of materials and frequently, this is accomplished with activated carbon impregnated with organic bases. Previous studies have used DFT and the graphite (0001) surface as a surrogate for adsorption, those studies focus on the species I•, I2, and CH3I. In this work we perform an ab initio study of the adsorption onto the surface of a graphite sheet of I2, CH3I, and inorganic acidic iodine species (HI, HOI, HIO2, and HIO3), which were selected to examine the possible effect of oxidation state on adsorption. The PBE exchange-correlation functional with D3 dispersion was employed. It was found that for molecular iodine, the iodine atoms tended to either situate above the center of a hexagonal site on the graphite or directly atop a carbon atom with the lighter components resting closer to the graphite. For each species the relative binding energies spanned the range of 21–33 kJ mol-1 and graphite-iodine distance was in the range of 3.52–3.93 Å. In all cases we found no significant charge transfer between the iodine species and the graphite, thus we conclude that all the iodine species studied undergo strong physisorption to the graphite.

A. V. Shavlov, V. A. Dzhumandzhi, E. S. Yakovenko

An experimental setup has been created to study the electrocoalescence of submillimeter- and millimeter-sized water droplets on a hydrophobic dielectric surface. The dependences of the interdroplet distance on the droplet radius are studied. It is shown that drops on a hydrophobic surface exhibit patterns of spatial arrangement that are characteristic of drops of a droplet cluster and fog. The electric field strengths at which mass coalescence of droplets begin are measured. A new model of electrocoalescence based on the state diagram of a drop-ion plasma is proposed. The possible role of electrocoalescence in the problem of rapid rain formation in atmospheric clouds is discussed.

Huiling LI

Inevitably China will encounter the enormous demand of large-capacity power transmission over long-distance transmission from the west to the east in the future. With regards to such emerging requirement, a cluster-connected western sending terminal DC grid based on VSC-HVDC is constructed in this paper such that the complementary regulation is performed between different power sources such as wind power, solar power, hydro power and thermal power in Western China, and the problem of randomness and fluctuation of renewable energy can also be addressed. The simulation system of the western sending terminal DC grid is set up based on the studies of the steady-state model, transient model and coordinated control strategy. Furthermore, the steady-state operation characteristics and transient operation characteristics of the western sending terminal DC grid are analyzed, as well as the impact of large renewable energy generation fluctuation on the operation of DC grid. The results show that, in view of the power change of the renewable energy converter stations caused by AC/DC fault and power fluctuation due to the weather reasons, power generation can be coordinated among the converter stations to achieve emergency backup of all kinds of energy sources and reduce the disturbance impact. Therefore, the western sending terminal DC grid can realize the stable long-distance transmission of large-scale renewable energy.

Peng Zhang, Feng Cai, Guo-Jie Wang et al.

Liangyu Huang, G. Shen, N. Hu et al.

Induction motors are complex energy conversion systems across the domains of dynamics, electricity, and magnetism. Most existing models mainly consider unidirectional coupling, such as the effect of dynamics on electromagnetic properties, or the effect of unbalanced magnetic pull on dynamics, while in practice it should be a bidirectional coupling effect. The bidirectionally coupled electromagnetic-dynamics model is beneficial to the analysis of induction motor fault mechanisms and characteristics. This paper proposes a coupled electromagnetic-dynamic modeling method that introduces unbalanced magnetic pull. By using the rotor velocity, air gap length, and unbalanced magnetic pull as the coupling parameters, the coupled simulation of the dynamic and electromagnetic models can be effectively realized. Simulation results for bearing faults show that the introduction of magnetic pull induces a more complex dynamic behavior of the rotor, which in turn leads to modulation in the vibration spectrum. The fault characteristics can be found in the frequency domain of the vibration and current signals. Through the comparison between simulation and experimental results, the effectiveness of the coupled modeling approach and the frequency domain characteristics caused by the unbalanced magnetic pull are verified. The proposed model can help to obtain a variety of information that is difficult to measure in reality and can also serve as a technical basis for further research on nonlinear characteristics and chaos in induction motors.

Tianhao Liu, Kai Shang, C. Miao et al.

Here in this article, a halloysite nanotube/reduced graphene oxide/cobalt nickel composite (HNT/rGO/CoNi) was synthesized by co-precipitation and subsequent calcination processes. The microstructure, morphology, and chemical composition of the as-synthesized samples were characterized by X-ray diffractometer, Raman spectra, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The electromagnetic absorption performances of the composites/paraffin wax hybrids were tested in the frequency range 2-18 GHz. It was found that the synergistic attenuation of electricity and magnetism, as well as the fairly good impedance matching properties together have led to the impressive electromagnetic absorption performance of the optimized product. The maximum reflection loss can reach - 69.77 dB with the thickness of 2.38 mm at 14.72 GHz, and an effective absorption bandwidth of about 7.12 GHz (10.88 GHz-18.00 GHz) can be achieved in the HNT/rGO/CoNi (30) composite. The excellent microwave absorption performance was estimated to originate from the combination of multiple electromagnetic loss mechanisms, including interfacial polarization between graphene and magnetic nanoparticles, dipole orientation polarization caused by the defects of graphene, the natural ferromagnetic resonance, and eddy current of the magnetic nanoparticles. Furthermore, the halloysite plays the roles of improving dispersion of the magnetic nanoparticles as well as adjusting the complex permittivity of the composite. This work provides a new strategy for the design and fabrication of high performance microwave absorbing materials with natural and readily available components.

Yening LAI, Ke FENG, Tongwei YU et al.

The power grid safety and stability control system has limited terminal resources and high requirement for real time response, and existing authentication schemes can hardly satisfy the requirements of the system for safety, real-time ability and storage efficiency. By combining the distributed Hash table (DHT) technology with the blockchain technology, a blockchain distributed storage optimization method is firstly proposed based on DHT of Skip Graph structure. And then a distributed authentication scheme of power grid safety and stability control terminals is designed based on DHT and blockchain technology, and the process and key algorithms for terminal registration, network access and authentication are given. The safety and spatial-temporal complexity of the proposed scheme are analyzed. The authentication scheme is systematically implemented, and experiments are performed on its average authentication latency and average terminal storage cost, which has verified the feasibility of the proposed scheme and its advantages in spatial-temporal efficiency. The proposed scheme improves the communication safety between terminals of the power grid safety and stability control system without affecting the communication efficiency, thus ensuring the safe and stable operation of power grid.

Yong Xu, Dejun Feng, Junjie Wang et al.

Abstract The micro‐motion target can perform micro‐Doppler modulation on the electromagnetic wave due to motion components in different directions, leading to the defocus effect of the target imaging feature along the azimuth direction. This phenomenon has been widely concerned and investigated in the field of target recognition and anti‐recognition. However, the micro‐motion target fails to transform image features along the distance direction according to its slow mechanical modulation speed. In comparison, electromagnetic metasurfaces can flexibly control the characteristics of electromagnetic waves with faster modulation speed through electronic control. It can realize the image feature transformation along the range direction. Inspired by this idea, a joint modulation method of rotational micro‐motion and electronic control through an active frequency selective surface (AFSS)‐loaded rotating Luneberg lens reflector is proposed. The signal models of micro‐motion modulation and non‐periodic AFSS modulation are established separately. On this basis, the imaging properties of the joint modulation are further analysed and the two‐dimensional (2D) defocusing phenomenon of the image is discovered. Moreover, the simulation of the measured synthetic aperture radar (SAR) data with different modulation methods is conducted to demonstrate the effectiveness of the proposed method.

Zhaoqi Zhang, Hui Song, Xianglin Meng et al.

Abstract Temperature is an important environmental factor during the operation of gas‐insulated switchgear (GIS), affecting the evaluation results of the GIS equipment to increase the risk of the power system. However, the influence of temperature on the partial discharge detection signal of GIS is still unclear. Aimed at the common void defects in GIS, the law of change on the number of ultrahigh‐frequency (UHF) pulses, the UHF amplitude, the characteristic value of the UHF map, and the maximum apparent charge of a single pulse with temperature are obtained using the UHF method and IEC60270, and corresponding theoretical analysis is carried out. The results show that an increase in temperature leads to a decrease in the void discharge delay time, causing an increase in UHF pulses and a decrease in the apparent charge of a single discharge pulse in the experiment. The increase of temperature makes the void discharge current rise quickly so that the induced UHF amplitude increases. In the range of 40–70°C, the maximum pulse amplitude increases by approximately 30% for every 10°C increase, and the average pulse amplitude increases by approximately 12%. The result of UHF signals affected by temperature obtained in this study has research significance for the realisation of a comprehensive evaluation of the insulation state of GIS equipment considering temperature.

Jinfeng He, Shuting Liang, Fengjiao Li et al.

Abstract Liquid metals (LM) have shown a very broad development prospect over the past decades. This review article focuses on the latest research dedicated to liquid metal materials and their applications in five significant areas: stretchable conductive composite, intelligent sensing electronic skin, catalysis, 3D printing material, and driving machines. The fabrication, specific properties and application of stretchable liquid metal‐polymer composites that can be used as self‐healing materials have been summarized. Liquid metal deposition printing technology, liquid phase 3D printing, suspension 3D printing technology, micro‐contact printing technology, and in vivo 3D printing molding technology have also been reviewed. Furthermore, the application of liquid metal catalyst in aldehyde reaction, photocatalysis, and electrocatalysis have been discussed. We have shown that electricity, magnetism, sound, light and heat could stimulate the movement of liquid metal. Through this comprehensive overview of the latest research, the main practical application, development, and mechanism of liquid metal were summarized and described. The future development of liquid metal technology was prospected, thus providing a strong basic research support for the further development of LM materials and their applications.

Ning Hou, Minghai Wang, Ben Wang et al.

Liming Zhou, Shuhui Ren, G. Meng et al.

Abstract The node-based smoothed radial point interpolation method for solving the transient responses of magneto-electro-elastic structures in thermal environment is proposed. Considering the coupling relations between the elasticity, magnetism, electricity and heat, the generalized displacement (displacement, electric potential and magnetic potential) is calculated using the modified Newmark method. G space theory and the weakened weak formulation are applied to derive the equations of node-based smoothed radial point interpolation method for the magneto-electro-thermo-elastic multi-physics coupling problems. We use triangular background meshes as they could be generated more easily for structures with complex geometry. In some cases, they could even be created automatically. Detailed numerical study has shown that node-based smoothed radial point interpolation method not only successfully overcomes the overly-stiff behavior in the FEM and provides more accurate results, but also works well with distorted meshes. Therefore, the node-based smoothed radial point interpolation method could be adopted to solve the magneto-electro-thermo-elastic multi-physics coupling problems in practical engineering.