Hasil untuk "Electricity and magnetism"

R. Winkler, U. Zülicke

Electric and magnetic multipole densities in crystalline solids, including the familiar electric dipole density in ferroelectrics and the magnetic dipole density in ferromagnets, are of central importance for our understanding of ordered phases in matter. However, determining the magnitude of these quantities has proven to be conceptually and technically difficult. Here we present a universally applicable approach, based on projection operators, that yields gauge-invariant absolute measures for all types of electric and magnetic order in crystals. We demonstrate the utility of the general theory using concrete examples of electric and magnetic multipole order in variants of lonsdaleite and diamond structures. Besides the magnetic dipole density in ferromagnets, we also consider, e.g., the magnetic octupole density in altermagnets. The robust method developed in this work lends itself to be incorporated into the suite of computational materials-science tools. The multipole densities can be used as thermodynamic state variables including Landau order parameters.

Apekshya Ghimire, Chandralekha Singh

In this research, we investigated the impact of peer collaboration and changes from individual to group performance of graduate students on the Conceptual Survey of Electricity and Magnetism (CSEM) without any guidance from the instructor. We define construction of knowledge as a case in which the group answered the question correctly but in the individual administration of the survey before the group work, one member gave the correct answer and the other gave incorrect answer. We find that there was a significant improvement in the performance of students after peer interaction, which was mostly attributed to construction of knowledge. However, students had very few opportunities to co-construct knowledge as there were hardly any situations in which neither student in a group provided a correct answer. We analyzed the effect size for improvement from individual to group scores for each CSEM item to understand the characteristics of these questions that led to productive group interaction. We also compared the group performance of the graduate students to the introductory physics students in a prior study using the CSEM to get insight into the concepts that showed differences for the two groups and those that were challenging for both groups of students before and after collaboration with peers. Our findings can motivate physics instructors to incorporate group interactions both inside and outside of the classroom even without instructor's involvement so that students at all levels can learn from each other and develop a functional understanding of the underlying concepts.

Yunping Bai, Zhihui Liu, Mengmeng Duan et al.

With the help of photonic techniques, microwave photonic links (MPLs) have remarkable advantages in terms of generating, transmitting, and processing analog or microwave signals with high frequency or wide bandwidth relative to traditional electrical systems, which have been widely and deeply researched over the past few decades. Recently, significant advances in photonic integrated technologies have stimulated and promoted the emergence of high-performance integrated components that make up MPLs, thereby greatly enriching their capabilities and further expanding their application prospects. Here, we review the recent advances in MPLs, which involve high-performance MPLs, MPLs for microwave photonic radar systems, MPLs for optical signal processing, and MPLs for optical neuromorphic computing. Firstly, key parameters of MPLs performance are analyzed, and the approaches to constructing high-performance (i.e., broadband and large dynamic range) MPLs are summarized. Secondly, the architecture of MPLs used for different function modules of microwave photonic radar systems is reviewed, wherein the recent schemes based on MPLs are classified according to radar signal generation, radar signal processing, and radar signal transmission. Thirdly, the existing system schemes of MPLs for implementing optical signal processing are outlined, which include microwave photonic filters, integrators, channelizers, and phased array antennas. Fourthly, the photonic neuromorphic computing systems, a nascent flourished applications field engendered by integrated or partially integrated MPLs, are introduced and reviewed, which provide readers with a novel understanding of MPL and its potential applications. Finally, we briefly present our outlook on key technologies needed to further advance MPL techniques and their relative applications.

Zhen XIAO, Yanfeng GU, Yanze JIANG et al.

Small-footprint full-waveform Light Detection And Ranging (LiDAR) exhibits significant application potential owing to its high penetration capability and ability to capture complete echo data. However, the efficient and accurate processing of massive echo signals remains a crucial challenge for practical use, particularly in advancing waveform decomposition technology. In small-footprint full-waveform LiDAR systems, most echoes are single-target, while only multi-target echoes require detailed decomposition. Current solutions often sacrifice precision by employing simplified rapid waveform decomposition algorithms or process all echoes indiscriminately, resulting in low efficiency and the inability to balance accuracy and speed effectively. This study proposes a spatiotemporal coupling model-driven lightweight algorithm for detecting multi-target echoes in small-footprint full-waveform LiDAR. For the first time, it achieves efficient and accurate detection of multi-target echoes from waveform data with unknown echo counts. The proposed method eliminates redundant computations caused by indiscriminate processing of single-target echoes, significantly reducing waveform decomposition iterations. The technical contributions include constructing a spatiotemporal coupling echo signal model that captures the spatiotemporal characteristics of echo transmission, implementing model-driven lightweight waveform parameter estimation through double Gaussian function superposition fitting, and introducing an adaptive correlation discrimination method based on a signal-to-noise ratio approach. By leveraging the consistency of system-emitted pulses, the proposed method enables lightweight yet accurate multi-target echo detection. Experimental results on terrestrial and airborne waveform datasets demonstrate that our algorithm achieves 98.4% detection accuracy with a 93.1% recall rate. When integrated with four waveform decomposition methods, it improves processing efficiency by 2–3 times. The efficiency gain becomes even more pronounced as the proportion of single-target echoes increases.

Yongkun SONG, Tianxing YAN, Ke ZHANG et al.

Low-frequency Ultra-WideBand (UWB) radar offers significant advantages in the field of human activity recognition owing to its excellent penetration and resolution. To address the issues of high computational complexity and extensive network parameters in existing action recognition algorithms, this study proposes an efficient and lightweight human activity recognition method using UWB radar based on spatiotemporal point clouds. First, four-dimensional motion data of the human body are collected using UWB radar. A discrete sampling method is then employed to convert the radar images into point cloud representations. Because human activity recognition is a classification problem on time series, this paper combines the PointNet++ network with the Transformer network to propose a lightweight spatiotemporal network. By extracting and analyzing the spatiotemporal features of four-dimensional point clouds, end-to-end human activity recognition is achieved. During the model training process, a multithreshold fusion method is proposed for point cloud data to further enhance the model’s generalization and recognition capabilities. The proposed method is then validated using a public four-dimensional radar imaging dataset and compared with existing methods. The results show that the proposed method achieves a human activity recognition rate of 96.75% while consuming fewer parameters and computational resources, thereby verifying its effectiveness.

Dariusz Korzec, Florian Freund, Christian Bäuml et al.

The generation of ozone by dielectric barrier discharge (DBD) is widely used for water and wastewater treatment, the control of catalytic reactions, and surface treatment. Recently, a need for compact, effective, and economical ozone and reactive oxygen–nitrogen species (RONS) generators for medical, biological, and agricultural applications has been observed. In this study, a novel hybrid DBD (HDBD) reactor fulfilling such requirements is presented. Its structured high-voltage (HV) electrode allows for the ignition of both the surface and volume microdischarges contributing to plasma generation. A Peltier module cooling of the dielectric barrier, made of alumina, allows for the efficient control of plasma chemistry. The typical electrical power consumption of this device is below 30 W. The operation frequency of the DBD driver oscillating in the auto-resonance mode is from 20 to 40 kHz. The specific energy input (SEI) of the reactor was controlled by the DBD driver input voltage in the range from 10.5 to 18.0 V, the Peltier current from 0 to 4.5 A, the duty cycle of the pulse-width modulated (PWM) power varied from 0 to 100%, and the gas flow from 0.5 to 10 SLM. The operation with oxygen, synthetic air, and compressed dry air (CDA) was characterized. The ultraviolet light (UV) absorption technique was implemented for the measurement of the ozone concentration. The higher harmonics of the discharge current observed in the frequency range of 5 to 50 MHz were used for monitoring the discharge net power.

A. Krupka, M.-C. Firpo

We consider a visco-resistive magnetohydrodynamic modelling of a steady-state incompressible tokamak plasma with a prescribed toroidal current drive, featuring constant resistivity η and viscosity ν. It is shown that the plasma velocity root-mean-square behaves as ηf(H) as long as the inertial term remains negligible, where H stands for the Hartmann number H≡(ην)−1/2, and that f(H) exhibits power-law behaviours in the limits H≪1 and H≫1. In the latter limit, we establish that f(H) scales as H1/4, which is consistent with numerical results.

Yuxuan YANG, Dongliang GAO, Yiming CHEN et al.

For the problem of low-carbon dispatch of gas-power integrated energy system, gas-grid hydrogen blending, carbon capture and electricity-to-gas conversion are all effective technical means. Meanwhile, carbon trading mechanism is also an effective economic means to control carbon emission. Therefore, this paper constructs a carbon capture plant model with liquid-rich and liquid-poor tanks, combined with an electric-to-methane technology model to flexibly recover and utilize CO2 in the system. Secondly, a gas-grid hydrogen blending technology model is used to improve energy efficiency, while considering the nodal calorific value change constraint during gas-grid hydrogen blending. Then the sum of incentive carbon trading cost and operation cost is used as the objective function. Finally, an arithmetic test is carried out based on the improved Belgian 20-node natural gas system and IEEE 39-node power system models. The results verify that the integrated consideration of carbon capture, gas network hydrogen blending and incentive carbon trading mechanism can improve the low carbon economic dispatch of the system. The carbon price and incentive factor can be adjusted flexibly to regulate the system carbon emission level.

A. Khan, J. S. Roy

Massive MIMO (multiple-input multiple-output) is a multi-user MIMO technology that can provide high-speed multimedia services in 5G wireless networks using sub-6 GHz and millimeter wave bands. The massive MIMO (MMIMO) installs array antennas in the base stations, using hundreds of transceivers with other RF modules. One of the drawbacks of the MMIMO system is its huge power consumption, and the beamforming network with RF modules for a large number of antennas is the main contributor to the power consumption. In this paper, a novel beamforming method is proposed for the low power consumption of an MMIMO system. The proposed thinned smart antenna (TSA) of a semi-circular array produces a secure beam toward the user’s terminal with reduced interference. By thinning the antenna array, some of the antenna elements are kept off, resulting in less power consumption, while the array pattern remains the same as a fully populated array with a reduced side lobe level (SLL). The sub-6 GHz band of 5 GHz is used for the design of thinned array antennas. The genetic algorithm (GA) is used to determine the array sequence in thinning, and the adaptive signal processing algorithms least mean square (LMS), recursive least square (RLS), and sample matrix inversion (SMI) are used for the beamforming of the TSA, and the corresponding algorithms are GA-LMS, GA-RLS, and GA-SMI. The power saving of 40% to 55% is achieved using TSA. The maximum SLL reductions of 13 dB, 12 dB, and 14 dB are achieved for TSA using GA-LMS, GA-RLS, and GA-SMI algorithms, respectively.

Jun YAO, Yongfei WU, Yali WANG et al.

In recent years, China has perfected the executive mode of two-part electricity price policy by increasing users’ options. This paper uses the social welfare model to analyze the impact of the implementation of the national adjustment two-part electricity price system on the efficiency of market resource allocation in the year of 2016. Results show that the relaxation of the change cycle of the two-part pricing system can reduce the basic electricity price burden of enterprises, who have stopped production or half stopped production. However, it is not beneficial to the efficient production enterprises, which is not conducive to promoting the survival of the fittest in enterprises as a whole, and reduces the long-term utility of the whole society. The empirical results also show that The change of the two-part electricity price policy led to the decline of the total social welfare, which was reflected in the drop of the load rate by 7%. Meanwhile, it also reduces the fairness among users, which is reflected in the capacity utilization rate dropping by 30.6%. We believe that simply adjusting the executive mode of the electricity price policy is not conducive to the optimal allocation of power resources, and all enterprises should adopt the fair electricity price policy at the same time.

Wenqin WANG, Shunsheng ZHANG

Due to the range dependence and time-varying array factor of Frequency Diverse Array (FDA) radar, it can overcome the miss of range variable in traditional phased-array factor and gain loss of Multiple-Input Multiple-Output (MIMO) radar array. In recent years, FDA radar techniques have attracted more and more attention of researches and institutions. Nevertheless, there are still many open problems to be solved in FDA radar system theory, signal processing and application implementation. In this overviewing paper, we introduced the FDA concepts, motivation and extending techniques. The latest research advances on FDA radars and their applications are comprehensively reviewed, and the typical application prospects of FDA in jamming radar and radar anti-jamming, ambiguous clutter suppression and blind velocity target detection together with localization deception are discussed. Finally, several key research problems that need to be solved in future work are pointed out.

Júlia Karnopp, Bernardo Magaldi, Julio Sagás et al.

Global modeling of inductively coupled plasma (ICP) reactors is a powerful tool to investigate plasma parameters. In this article, the argon ICP global model is revisited to explore the effect of excited species on collisional energy through the study of different approaches to particle and energy balance equations. The collisional energy loss is much more sensitive to modifications in the balance equations than the electron temperature. According to the simulations, the multistep ionization reduces the collisional energy loss in all investigated reaction sets and the inclusion of heavy species reactions has negligible influence. The plasma parameters obtained, such as total energy loss and electron temperature, were compared with experimental results from the literature. The simulated cases that have more excited species and reactions in the energy balance are in better agreement with the experimental measurements.

Hyunwoong Shin, Hyeongdong Kim

Parallel loop feed structures can be used to implement wideband impedance. However, when a parallel loop feed structure is employed, parasitic resonance occurs in certain feed structures, resulting in the degradation of radiation efficiency. This is caused by the inductance and capacitance of the shunt line that is added to achieve the wideband impedance. We compared two antennas, one with a high impedance level and another with a low impedance level, by adjusting the ratio of the inductance to the capacitance of the parasitic resonance. When the parasitic resonance has a high impedance level, there is an improvement in the impedance bandwidth as well as the radiation efficiency of the antenna.

Volodymyr Krasnoholovets

It is shown that a magnetic monopole appears as the tension state of the primary electric charge at its motion through each section of the path equal to the particle's de Broglie wavelength. This conclusion is followed from a submicroscopic consideration of particles and their motion in the framework of the theory of physical space in the form of a tessellattice developed by Michel Bounias and the author. The periodical change of the particle's charged state to its monopole state can easily be introduced in the conventional Maxwell equations and the magnetic monopole automatically shows up in the structure of Maxwell's equations. The monopole is also presented in any quark system as a quark obeys dynamics that are also characterized by the appropriate de Broglie wavelength and hence the electric charge changes periodically to the magnetic monopole. A (anti)neutrino emerges as the typical electron's monopole. When the charged particle becomes the monopole, it also loses its mass (the mass passes to the particle's inerton cloud) and thus the neutrino is a massless particle, or more correctly massless monopole.

Mehdi Bozorgi

Abstract This study developed a generalized solution based on modal expansion for scattering by large cavities with known wave functions placed in an infinite perfect electric plane. Under the assumption of a large cavity, to reduce simulation time and simplify expressions, the half‐space above cavity with a strong singular Green's function is substituted by an arbitrary semi‐waveguide. The fields inside the cavity are expanded by the semi‐waveguide eigenfunctions. The corresponding modes are matched to create a system of linear equations for unknown expansion coefficients. To demonstrate the validity and ability of this method, it is applied to several grooves with different shapes (triangular, circular, and elliptical grooves) and then their scattering signatures are compared with each other. The results are also verified by the results obtained by the method of moment. The measured simulation time for both methods shows that this scheme can be an appropriate candidate for analysing the scattered fields by large cavities.

Mei Li, Jie Lu

Chirality and current-driven dynamics of topologically nontrivial 360$^{\circ}$ domain walls (360DWs) in magnetic heterostructures (MHs) are systematically investigated. For MHs with normal substrates, the static 360DWs are Néel-type with no chirality. While for those with heavy-metal substrates, the interfacial Dzyaloshinskii-Moriya interaction (iDMI) therein makes 360DWs prefer specific chirality. Under in-plane driving charge currents, as the direct result of "full-circle" topology a certain 360DW does not undergo the "Walker breakdown"-type process like a well-studied 180$^{\circ}$ domain wall as the current density increases. Alternatively, it keeps a fixed propagating mode (either steady-flow or precessional-flow, depending on the effective damping constant of the MH) until it collapses or changes to other types of solition when the current density becomes too high. Similarly, the field-like spin-orbit torque (SOT) has no effects on the dynamics of 360DWs, while the anti-damping SOT has. For both modes, modifications to the mobility of 360DWs by iDMI and anti-damping SOT are provided.

S. V. Zubkov

The Aurivillius phases (APs) [Bi2O2]2+[Am−1BmO3m+1]2− are well-known ferroelectrics with high Curie temperatures. High-temperature piezoceramics Bi3−xGdxTiNbO9(BiGdTiNb, x=0, 0.1, 0.2, 0.3) were prepared by a solid-state reaction method. The structural and electrophysical characteristics of BiGdTiNb ceramics have been studied. According to the data of powder X-ray diffraction, all the compounds are single-phase with the structures of two-layer APs (m=2) with the orthorhombic crystal lattice (space group A21am). The temperature dependence of the relative permittivity ε∕ε0 (T) of the compounds was measured and showed that the Curie temperature of perovskite-like oxides Bi3−xGdxTiNbO9 increases linearly with an increase in the substitution parameter x to TC=950∘C. The activation energies of charge carriers have been found in different temperature ranges.

GONG Jin-chang, WANG Yu, WANG Yuan-jun

An automatic algorithm based on wavelet fusion is proposed for segmenting brain glioma with blurred boundaries and complex intratumoral structures on multimodal magnetic resonance (MR) images. Firstly, the T1, T1ce, T2 and Flair MR images of brain glioma are fused with the bias field corrected. Secondly, the image blocks to be classified are extracted, and the 3D-UNet network is trained to classify the pixels in the image blocks. Finally, the trained network model is used for segmentation, and the contour extraction method based on connected regions is used to reduce false positives. The average segmentation accuracy (DSC) of the whole, core and edema parts of the tumors was found to be 90.64%, 80.74% and 86.37%, respectively. The results indicated that the accuracy of the algorithm proposed was similar with or higher than the gold standard method. Compared with the method without multimodal image fusion, the algorithm proposed not only reduced the amount of data and redundant information in the input network, but also improved the accuracy and robustness of segmentation.

YUE Qing, WANG Yuan-jun

Fiber tracking with diffusion magnetic resonance imaging provides a powerful tool for non-invasive observation of white matter in the brain. Constrained spherical deconvolution (CSD) is a multi-fiber tracking model, which can model the orientation of fibers in the voxel and achieve brain fiber reconstruction. This paper proposes a deterministic fiber tracking algorithm based on a non-local CSD model that combines neighborhood information and fractional regularization. The algorithm aimed to solve the ill-posed problem and loss detailed information in the conventional CSD model. The nonlocality of fractional order reduced the errors of fiber orientation distribution estimation, and the neighborhood information was used to ensure spatial consistency, reducing the effects of random noise. Simulation data and experimental human brain data were used to compare the performance of the proposed algorithm and the conventional CSD deterministic tracking algorithm. The results demonstrated that the proposed algorithm produced not only better overall visual effect, but also more complete and accurate reconstruction of the crossing fibers.

Yuanjian SONG, Zheng XU, Jingqiu YU et al.

The modeling of wind turbine tower is an important part of the research on lightning protection of offshore wind turbines. The establishment of its model has an important impact on the analysis results. This paper first analyzes the inapplicability of the tower multi-surge impedance model in the research of lightning protection for offshore wind turbines, and then establishes a non-uniform transmission line model of tower. Secondly, the influence of the spatial structure change of the tower on its own electromagnetic transient characteristics was studied by using the multi-surge impedance model. The results show that the more the tower is divided into sections, the more accurate its electromagnetic transient response is. Finally, a comparative analysis of the lightning transient response of the tower using the non-uniform transmission line model and the multi-surge impedance model is performed, which proves that the non-uniform transmission line model is more in line with actual conditions.