Hasil untuk "Electricity and magnetism"

CAO Fei, XU Qianqian, CHEN Hao et al.

Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disease primarily diagnosed through diffusion-weighted imaging (DWI). However, the limitation of human visual interpretation and clinical experience can lead to inaccuracies in diagnosis. This research proposes a deep learning method based on cross self-supervision, alongside the construction of Co-ResNet50 and CO-ViT models for intelligent auxiliary diagnosis of NIID. This method uses self-supervised learning and effectively combines the characteristics of ResNet50 and ViT networks to improve the model’s feature extraction capabilities. The experiment preprocessed 249 DWI data and divided them into 204 training sets and 45 test sets. The results reveal that the CO-ResNet50 model has the best performance, with an accuracy of 95.49%, precision of 95.51%, recall of 95.44%, F1 score of 0.954 7, and AUC of 0.989 7. These findings underscore the model's potential to provide support for clinical NIID diagnosis.

Bo ZHANG, Congbo WANG, Rongrong ZHAN et al.

The VSC-HVDC transmission system for large-scale new energy has become a typical scenario in China's new power system. However, the transmission line between the new energy station and the flexible direct converter is special with its both sides being power electronic devices, and affected by different converter control strategies, the short-circuit current waveform is seriously distorted, which reduces the sensitivity of traditional longitudinal protection and increases the risk of rejection. Therefore, an adaptive current differential protection method considering control and protection coordination is proposed. Based on the fault ride throgh strategy of the VSC-HVDC, the fault current characteristics on both sides are analyzed, and an adaptive protection criterion for control and protection coordination is constructed by combining the control reference value of the converter and the protection criterion. Finally, a VSC-HVDC transmission system model for new energy is built based on PSCAD, and the performance of the proposed protection is verified by simulation. The results show that the proposed protection can quickly identify different fault types in the fault region with the sensitivity improved by 2~3 times compared with the traditional differential protection principle, which can meet the requirements of the new power systems for protection sensitivity and reliability.

Jianjun GE, Siqi TANG, Mingqiang LI et al.

This paper addresses the challenges of adapting complex perception systems to perform core tasks such as detection, tracking, and countermeasures in highly dynamic and adversarial battlefield environments. We propose an information-driven theoretical model and a systematic methodology for system construction. This study introduces an information-driven theoretical model and construction methodology for such systems. Specifically, a multi-layered information description framework is introduced to overcome the application barriers of traditional static modeling and fixed-pattern design. This framework is based on syntax, semantics, and pragmatics and is designed to overcome the limitations of single syntactic structures and surface-level semantics. A dynamic evolution architecture is incorporated into the system. The theoretical achievements are also applied to the practice of distributed radar detection systems. Moreover, a structured hierarchical optimization algorithm with a finite-scenario interactive learning mechanism is designed to achieve ordered system organization and capability emergence, thereby addressing the complexity of system optimization. This study provides a theoretical framework and technical approach for the design of intelligent perception systems in complex battlefield environments.

Hongcheng ZHOU, Xiaoran YU, Yu WANG et al.

Metasurfaces are two-dimensional artificial structures with numerous subwavelength elements arranged periodically or aperiodically. They have demonstrated their exceptional capabilities in electromagnetic wave polarization manipulation, opening new avenues for manipulating electromagnetic waves. Metasurfaces exhibiting electrically controlled reconfigurable polarization manipulation have garnered widespread research interest. These unique metasurfaces can dynamically adjust the polarization state of electromagnetic waves through real-time modification of their structure or material properties via electrical signals. This article provides a comprehensive overview of the development of metasurfaces exhibiting electrically controlled reconfigurable polarization manipulation and explores the technological advancements of metasurfaces with different transmission characteristics in the microwave region in detail. Furthermore, it delves into and anticipates the future development of this technology.

Boxue Du, Guoning Sun, Heyu Wang et al.

Abstract The authors focus on the impact of melt‐free radical grafting with hindered phenolic antioxidants (AO3052) on the electrical properties of polypropylene (PP) for DC cable insulation. The DC conductivity, space charge distribution and breakdown characteristic tests of grafting‐modified PP are performed by comparing unmodified PP. The results demonstrate that the grafting of antioxidants can effectively suppress space charge injection, owing to the deeper trap sites at the grafting molecule. The breakdown strength of the grafted PP is significantly enhanced from 30°C to 90°C and especially achieves a 5.3%–6.7% increase after the same DC‐prestressed time at 90°C. The surface electrostatic potential and molecular orbitals of the grafted PP are calculated. Simulation shows that the antioxidant introduces multi‐level local state traps that can effectively trap the injected space charge, thus decreasing the destruction of molecular chains by electrons and increasing the breakdown strength level. In conclusion, antioxidant grafting modification can improve the breakdown characteristics with or without DC prestress, and thus it appears to be promising in the application of PP‐insulated cables.

Vadim Pavlovich Markovskiy, Dauren Dzhambulovich Issabekov, Viktor Yuryevich Mel’Nikov

This paper presents the development and principle of operation of resource-saving overcurrent protection, which is an alternative to traditional current protections. The experiments were used to study the electromagnetic field for the protection of electrical installations connected to the cells of complete switchgears, voltage 6–10 kV, without the use of conventional protections with metal-core current transformers. As is known, such current transformers (CTs) have significant weight and dimensional parameters and high price costs. The method of research is comparison of the developed protection with traditional current protections made using traditional measuring current transformers. The scientific novelty of this work consists of the developmental theory of the construction of protection for inductive coils based on the measurement of electromotive force values in different modes and points in the simulation of a three-phase short circuit inside the cell of the complete switchgear. The dependence of magnetic induction on the position of the inductive coil inside the cell has been found. It has been shown that the simplest formula of the Biot–Savart–Laplace law can be used to calculate them. This paper presents and describes the conducted experiments with their methodology. As a result of the industrial application of such protections, the act of implementation of the patent for the invention of an industrial enterprise is presented. The selection of settings of resource-saving protection is presented, as well as a feasibility study of the presented protection in comparison with conventional protection. This paper consists of the following sections: The Materials and Methods section describes the methodology used to achieve the purpose of the research. The Experiments section describes all the experiments conducted to achieve the purpose of the research. The Results section presents the results of the conducted experiments, an evaluation of the use of inductive coils in relay protection, an example of calculating the selection of the settings of parameters of resource-saving protection, a presentation of the patent for the invention, and a presentation of the feasibility study of the effectiveness of the considered resource-saving protection on inductive coils. The Conclusions section presents the result of this work, which is the creation of resource-saving protection on inductance coils. The References section presents a list of the sources used.

Zhaohong LI, Huaping XU, Shuhang DUAN et al.

The performance of Synthetic Aperture Radar (SAR) active deception jamming detection based on the interferometric phase is analyzed. Based on the slant-range local fringe frequency probability distributions of a real scene and a false target, the influences of the vertical baseline length, jamming-to-signal ratio, and local fringe frequency estimation window size on the True Positive Rate (TPR) are analyzed. Furthermore, when the False Positive Rate (FPR) is known, the vertical baseline length required for the SAR system to meet the detection probability requirements is analyzed, thereby providing a theoretical basis for the baseline design of the SAR system. Finally, the result of theoretical analysis is verified by simulation. The theoretical analysis and experimental results show that, for a certain false alarm probability, as the vertical baseline length, jamming-to-signal ratio, or local fringe frequency estimation window value increases, the detection probability also increases.

Manoj Kumar, Gowrish Basavarajappa

Abstract This paper presents the design of novel compact multifunctional coaxial to waveguide power combining transition (PCT) for X‐band applications. For the proof of the proposed concept, 2‐way PCT operating over the entire X‐band (8.2–12.4 GHz) and 4‐way PCT operation from 9.5 to 10.8 GHz are designed, developed, and characterised. Two‐way PCT achieves a measured return loss better than 14 dB over the operating band, and the measured amplitude imbalance and phase imbalance are within 0.25 dB and 4°, respectively. Four‐way PCT achieves a measured return loss better than 15 dB over the operating band, and the measured amplitude imbalance and phase imbalance are within 1 dB and 10°, respectively. Furthermore, a 6‐way PCT is also designed, fabricated, and measured to demonstrate the scalability of the proposed concept. The 6‐way PCT achieves the measured return loss better than 15 dB from 9.9 to 10.475 GHz, and measured amplitude and phase imbalances are within 0.6 dB and 10°, respectively. The designed power combining transition is proposed to be used in X‐band applications like antenna array applications and power combining applications.

Tetsu Anan, Roberto Casini, Han Uitenbroek et al.

The efficient release of magnetic energy in astrophysical plasmas, such as during solar flares, can in principle be achieved through magnetic diffusion, at a rate determined by the associated electric field. However, attempts at measuring electric fields in the solar atmosphere are scarce, and none exist for sites where the magnetic energy is presumably released. Here, we present observations of an energetic event using the National Science Foundation's Daniel K. Inouye Solar Telescope, where we detect the polarization signature of electric fields associated with magnetic diffusion. We measure the linear and circular polarization across the hydrogen H-epsilon Balmer line at 397 nm at the site of a brightening event in the solar chromosphere. Our spectro-polarimetric modeling demonstrates that the observed polarization signals can only be explained by the presence of electric fields, providing conclusive evidence of magnetic diffusion, and opening a new window for the quantitative study of this mechanism in space plasmas.

Urmimala Dey, Emma E. McCabe, Jorge Íñiguez-González et al.

The promise of a strong magnetoelectric coupling in a multiferroic material is not only of fundamental interest, but also forms the basis of next generation memory devices where the direction of magnetization can be reversed by an external electric field. Using group-theory led first-principles calculations, we have identified a hitherto unknown polar phase of the $A_4B_3\rm{O}_9$ layered oxides, where the polar mode couples to the magnetic modes through a rare $Γ$-point magnetoelectric-multiferroic coupling scheme such that the net magnetization can be directly reversed by an electric field switching of the polar mode. Furthermore, in agreement with previous experimental observations, we predict room temperature magnetism in $A_4B_3\rm{O}_9$ oxides which indicates the promising practical applications of these compounds in the next generation memory devices.

R. Casini, R. Manso Sainz, A. Lopez Ariste et al.

We extend the spherical tensorial formalism for polarization to the treatment of electric- and magnetic-multipole transitions of any order. We rely on the spherical-wave expansion to derive the tensor form of the operator describing the interaction of the atomic system with a polarized radiation field, which naturally leads to the introduction of spherical tensors describing the polarization properties of the interacting field. As a direct application, the formalism is used to model the radiation anisotropy affecting the scattering of radiation in an electric-quadrupole transition, and the associated Hanle effect in the presence of a magnetic field.

Dong-Su Choi, Yoon-Seon Choi, Hyo-Jin Lee et al.

In this study, a dual-mode waveguide circularly polarized antenna for TC&R (telemetry, command, and ranging) was proposed for the communication between a low-orbit satellite and a ground station. The proposed antenna required both a wide −10 dB bandwidth and axial ratio bandwidth of 7.1–7.3 GHz and 8.0–8.4 GHz. The antenna was designed with a stepped septum inside a square waveguide to obtain circular polarization and the axial ratio wide bandwidth. Next, a dual-mode synthesis method was adopted for link budgeting by combining square and circular waveguides. The requirement was that the co-polarization level with a symmetric −3 dB beamwidth of 39° must be −5 dBic or higher at ±76.5°, and the cross-polarization level must average −15 dBic or lower at ±76.5°. Finally, the corrugate structure attached to the outside of the extended circular waveguide was offset in multiple steps to suppress the back lobe of the cross-polarization As a result, the axial ratio maintained an average of 1.8 dB at 0° within each band of the required frequency. In addition, the co-polarization obtained an average of −4.52 dBic in the 7.2 GHz band and −5.31 dBic in the 8.2 GHz band at ±76.5°. Finally, in the case of the cross-polarization pattern, the back lobe level was suppressed by 9.89 dB at 7.2 GHz by the corrugate structure, and an average value of −19.9 dBic or less was obtained at ±76.5°. The proposed antenna was confirmed to be effective as a Korean low-orbit satellite TC&R antenna with a radiation pattern of a symmetric beamwidth.

Yiyi Zhang, Qianlun Du, Wenchang Wei et al.

Abstract Engineering experience shows that for transformers with long service life and serious moisture exposure, the inter‐turn paper insulation inside the winding will precipitate bubbles under the condition of electric field and conductor heating, which will endanger the equipment insulation. In order to explore the influence factors of bubbles formation in the moist insulating paper of transformers, based on the existing research on the influence of moisture content and gas dissolution in transformer oil, this study further considers the influence of air pressure (AP) and electric field and establishes an experimental platform to change the air pressure and electric field, thereby studying the formation characteristics of bubbles in oil‐paper insulation. The results show that air pressure and electric field can affect the initial temperature, volume, and shape of bubble formation. From 0 to −0.05 MPa for air pressure, the initial temperature of bubble generation decreased by 41°C, its maximum two‐dimensional projected area increased by 418.4% with more severe distortion, and the breakdown voltage decreased. When the AC voltage applied on the needle plate electrode increased from 0 to 10 kV, the initial temperature of bubble formation increased by 29°C, and the maximum two‐dimensional projection area increased by 336.6%.

Taejoo Sim, Dong-min Lee, Wansik Kim et al.

In this study, a dual-band low-noise amplifier (LNA) was implemented by applying a transformer-based neutralization technology to the W-band. Incorporating the neutralization technique was difficult owing to performance degradation in the W-band. However, circuit performance was enhanced thanks to the layout optimization of transformer-based neutralization networks, and the improved operation was confirmed in the W-band. The neutralization technique was implemented in four stages with a 0.1-μm gallium arsenide (GaAs) pseudomorphic high-electron-mobility-transistor monolithic microwave integrated circuit LNA. The LNA showed small signal gains of 20.3 dB and 21.7 dB and noise figures of 5.0 dB and 6.4 dB (at 84 GHz and 96 GHz, respectively) while consuming 46 mW from a 1-V supply.

Yilun LI, Yishu ZHANG, Guang SONG

The accurate and rapid identification of model parameters is crucial to the simulation of the hysteresis characteristics of current transformer cores based on the J-A hysteresis model. With regard to the difficulties in measuring the input and output of the existing J-A model parameters in addition to the slow convergence speed and low accuracy of the extraction method, a parameter extraction method of the ψ-i JA hysteresis model based on the improved whale algorithm is proposed in this paper. The model is established in terms of flux linkage and current instead of flux density and magnetic field. The parameters are extracted using an improved whale algorithm with adaptive adjustment of weights and search strategies. By taking advantage of the proposed method, particle swarm algorithm, and whale algorithm respectively, the hysteresis curves of P-type current transformer and PR-type current transformer are identified and compared. The result comparison shows that the improved whale algorithm has higher accuracy and fewer iterations, such that the high efficiency of the proposed method is verified.

Zunaira Nazir, Math H. J. Bollen

The increased complexity of the transmission grid can endanger the operational security of the grid. Operational risk assessment, a stochastic tool, helps to enhance security. Contingency analysis and its impact quantification are the main constituents of operational risk assessment. In this study, different graphical methods are proposed to visualize operational risk contingency-based detailed results: heat-map and risk-based contingency chart. Through the heat-map, the system operator can determine which contingencies contribute most to the operational risk and would therefore be the most threatening contingencies for operational security of the grid. The “risk-based contingency chart” allows the system operator to analyze contingency cases from the probability and impact aspect in one chart. Both tools may be used in the control room for improved operational planning. In this study of contingency analysis and various types of network studies of severity factor quantification, the IEEE 39-Bus sample network is used in Power-Factory to analyze the contingencies behavior under different operational scenarios.

Zhen-lin WANG, Rong ZHANG, Ni ZHANG et al.

Two-dimensional nuclear magnetic resonance (NMR) technology can perform non-destructive, rapid and quantitative measurement and characterization of various hydrogen-containing fluids in the reservoir, but is limited by the acquisition methods and parameters of NMR equipment. In the detection of samples with ultra-fast relaxation components such as organic matter and asphalt, the problem of missing or inaccurate fluid components in two-dimensional spectrum due to incomplete signal acquisition often occurs. In this paper, a high-precision inversion method of T2-T1 two-dimensional spectrum based on ultrafast relaxation component compensation technology is proposed. This method extends the one-dimensional NMR front-end signal compensation technology. By compensating the components of the echo data before the inversion of two-dimensional NMR data, the problem of signal leakage at the front end of two-dimensional NMR logging can be effectively solved. The application of experiments and logging data shows that this method can obtain more accurate and complete reservoir information in shale oil and other reservoirs rich in signals of fast relaxation components.

Anastasios G. Koutinos, George A. Kyriacou, John L. Volakis et al.

Abstract A novel antenna design technique is proposed, which offers bandwidth enhancement up to the limits defined by element radiation efficiency. The employed technique is referred as frequency pulling (FP) as it mimics the ‘insertion loss design methodology of band‐pass filters’. This is essentially a wideband matching approach pushing the antenna efficiency to the limits set up by radiation efficiency. There are three options towards this trend: (i) first to enhance a single element bandwidth (compact element) exploiting its possibly multiple symmetrical feeding points as distinct resonator ports, (ii) frequency pulled array as to design a small antenna array (less than about 10 elements) where each element acts as a resonator and (iii) second order frequency‐pulled array as to build a small array using compact elements of category (i). Similar to the band‐pass filter design, all antennas or distinct‐port circuits resonate at the same resonant frequency when isolated, cascading two or more of them; FP yields to multiple‐overlapping successive resonances in their overall response. Although the proposed technique is general within this first effort, it is applied to simple patch antenna elements exhibiting multiple symmetrical feeding points, namely two—for rectangular, four—for square and five—for pentagonal. The third option is applied to an array of three compact 4‐feeding point square elements offering triple bandwidth with respect to the already wideband single element. However, this is achieved at the expense of a significant beam squint. Thus, in general, these wideband compact elements should be used within a classical array design. Further bandwidth enhancement using FP to antenna elements with inherent multiple resonances as patches with slots or truncated edges constitutes our next task. Their inherent wider bandwidth in radiation efficiency is expected to allow multiply higher bandwidths when exploited with our FP technique.

Yu Chen, Qiang Fan, Yiding Liu et al.

Controlling magnetism and electronic properties of two-dimensional (2D) materials by purely electrical means is crucial and highly sought for high-efficiency spintronics devices since electric field can be easily applied locally compared with magnetic field. The recently discover 2D Janus crystals has provide a new platform for nanoscale electronics and spintronics due to their broken inversion symmetry nature. The intrinsic ferromagnetic Jauns monolayer, and hence the tunable physical properties, is therefore of great interest. Here, through comprehensive density functional theory calculations and Monte Carlo simulations, we unveil that single-layer MnSSe is an intrinsic ferromagnetic half-metal with a direct band gap of 1.14 eV in spin-down channel and a Curie temperature of about 72 K. The exchange coupling can be significantly enhanced or quenched by hole and electron doping, respectively. In particular, a small amount of hole doping MnSSe can tune its magnetization easy axis in between out-of-plane and in-plane directions, which is conducive to designing 2D spin field-effect transistor for spin-dependent transport. We also find a reversible longitudinal interlayer charge transfer between S and Se layers for the first time that is highly sensitive to the applied external electric field. Interestingly, the directions of charge flow and the applied field are the same. The behavior originates from the coexistence and/or the competition of external and built-in fields. These findings, together with the excellent stability and large in-plane stiffness, can greatly facilitate the development of nanoscale electronics and spintronics devices based on 2D MnSSe crystal.

Zheng HUANG, Hongxing WANG, Hang ZHOU et al.

The sequence of conventional shooting viewpoints for power tower is fixed and the inspection distance of multi-rotor UAV is not optimal. In addition, as the dimension increases, the path planning algorithm cannot meet the requirements of real-time path planning because the space complexity increases exponentially. Aiming at those problems, a three-dimensional path planning method for power tower inspection is proposed based on ant colony optimization and A * (ACO-A*) hybrid algorithm. The method is composed of global planning and local planning. Firstly, the global planning uses the ant colony optimization algorithm to find a relatively optimal path that covers all viewpoints, and to judge whether the path passes through obstacles. And then the A* algorithm is used for local planning. The simulation results show that the path length planned by the proposed ACO-A* algorithm is reduced by 16.68% compared to that stipulated in the Shooting Manual for UAV Inspection Images of Overhead Transmission Lines, and the path planning time is reduced by 99.68% compared to that of the A* algorithm. Therefore, the proposed method not only reduces the energy consumption for inspection, but also enhances the efficiency of path planning.