Hasil untuk "Electricity and magnetism"

Junyu WANG, Hao SUN, Qihao HUANG et al.

Synthetic Aperture Radar (SAR) is widely used in military and civilian applications, with intelligent target interpretation of SAR images being a crucial component of SAR applications. Vision-Language Models (VLMs) play an important role in SAR target interpretation. By incorporating natural language understanding, VLMs effectively address the challenges posed by large intraclass variability in target characteristics and the scarcity of high-quality labeled samples, thereby advancing the field from purely visual interpretation toward semantic understanding of targets. Drawing upon our team’s extensive research experience in SAR target interpretation theory, algorithms, and applications, this paper provides a comprehensive review of intelligent SAR target interpretation based on VLMs. We provide an in-depth analysis of existing challenges and tasks, summarize the current state of research, and compile available open-source datasets. Furthermore, we systematically outline the evolution, ranging from task-specific VLMs to contrastive-, conversational-, and generative-based VLMs and foundational models. Finally, we discuss the latest challenges and future outlooks in SAR target interpretation by VLMs.

Guillaume L. Giudicelli, Guillaume L. Giudicelli, Fande Kong et al.

High fidelity simulations of nuclear systems generally require a multi-dimensional representation of the system. Advanced nuclear reactor cores are governed by multiple physical phenomena which should be all be resolved, and the coupling of these physics would also need to be resolved spatially in a high-fidelity approach, while lower fidelity may leverage integrated quantities for the coupling instead. Performing a spatially resolved multiphysics simulation can be done on a single mesh with a single coupled numerical system, but this requires catering to each equations’ time and spatial discretization needs. Instead, each physics, usually neutronics, thermal hydraulics and fuel performance, are solved individually with the discretization they require, and the equations are coupled by transferring fields between each solver. In our experience coupling applications within the MOOSE framework, mostly for advanced nuclear reactor analysis, there are several challenges to this approach, from non-conservation problems with dissimilar meshes, to losses in order of spatial accuracy. This paper presents the field transfer capabilities implemented in MOOSE, and numerous technical details such as mapping heuristics, conservation techniques and parallel algorithms. Examples are drawn from nuclear systems analysis cases to illustrate the techniques.

Aimin TANG, Shuhan WANG, Wenze QU

With the emergence of the low-altitude economy, the communication and detection issues of Unmanned Aerial Vehicles (UAVs) have gained considerable attention. This paper investigates sensing reference signal design for Integrated Sensing And Communication (ISAC) in Orthogonal Frequency Division Multiplexing (OFDM) systems aimed at detecting long-range, high-speed UAVs. To address the ambiguity problem in long-range and high-speed UAV detection, traditional reference signal designs require densely arranged reference signals, leading to significant resource overhead. In addition, long-range detection based on OFDM waveforms faces challenges from Inter-Symbol Interference (ISI). To address these issues, this paper first proposes a reference signal pattern that supports long-range detection and resists ISI, achieving the maximum unambiguous detection range of the system with reduced resource overhead. Then, to address the challenge of high-speed detection, the paper incorporates range-rate into the Chinese Remainder Theorem-based method. Through the proper configuration of sensing reference signals and the cancellation of ghost targets, this approach significantly increases the unambiguous detection velocity while minimizing resource usage and avoiding the generation of ghost targets. The effectiveness of the proposed methods is validated through simulations. Simulation results show that compared with the traditional sensing reference signal design, our proposed scheme can reduce 72% overhead of reference signals for long-range and high-speed UAV detections.

Emanuele Greco

Magnetic turbulence plays a crucial role in confining charged particles near the shock front of Supernova Remnants, enabling them to reach energies up to hundreds of TeV through a process known as Diffusive Shock Acceleration (DSA). These high-energy electrons spiral along magnetic field lines, emitting X-ray synchrotron radiation. The launch of the Imaging X-ray Polarimetry Explorer (IXPE) has opened a new window into the study of magnetic fields in SNRs through X-ray polarization measurements. For the first time, IXPE allows us to resolve the polarization degree (PD) and angle (PA) in the X-ray band across different areas of SNRs, offering direct insight into the geometry and coherence of magnetic fields on different scales. In this mini-review, I summarize the key observational results on SNRs obtained with IXPE over the past four years and discuss their implications for our understanding of magnetic turbulence in synchrotron-emitting regions. I also show how we can combine polarization parameters and standard X-ray spectral/imaging analysis to better constrain the structure and scale of magnetic turbulence immediately downstream of the shock and understand the particle acceleration occurring in SNRs.

Rasmus Bjørk

A closed-form solution for the magnetic scalar potential generated by a uniformly magnetized cylindrical slice and a full cylinder is determined by solving Poisson's equation analytically. The solution is given in terms of elliptic integrals of the first, second and third kind. We show that the magnetic scalar potential can be written as the dot product of a demagnetization vector, containing all the geometric information of the generating cylinder, and the magnetization. We validate the derived analytical expressions for the magnetic scalar potential by comparing with a finite element simulation and show that these agree perfectly for both the cylindrical slice and the full cylinder.

Shengyao Li, Sabpreet Bhatti, Siew Lang Teo et al.

In alignment with the increasing demand for larger storage capacity and longer data retention, electrical control of magnetic anisotropy has been a research focus in the realm of spintronics. Typically, magnetic anisotropy is determined by grain dimensionality, which is set during the fabrication of magnetic thin films. Despite the intrinsic correlation between magnetic anisotropy and grain dimensionality, there is a lack of experimental evidence for electrically controlling grain dimensionality, thereby impeding the efficiency of magnetic anisotropy modulation. Here, we demonstrate an electric field control of grain dimensionality and prove it as the active mechanism for tuning interfacial magnetism. The reduction in grain dimensionality is associated with a transition from ferromagnetic to superparamagnetic behavior. We achieve a non-volatile and reversible modulation of the coercivity in both the ferromagnetic and superparamagnetic regimes. Subsequent electrical and elemental analysis confirms the variation in grain dimensionality upon the application of gate voltages, revealing a transition from a multidomain to a single-domain state accompanied by a reduction in grain dimensionality. Furthermore, we exploit the influence of grain dimensionality on domain wall motion, extending its applicability to multilevel magnetic memory and synaptic devices. Our results provide a strategy for tuning interfacial magnetism through grain size engineering for advancements in high-performance spintronics.

Electricity Editorial Office

High-quality academic publishing is built on rigorous peer review [...]

Qiwen Cheng, Jun Zou

Abstract In order to achieve high performance for solving the ion flow field problem, an approach is proposed with the tensor‐structured finite element method (FEM) to accelerate the Newton iteration. The Poisson equation and the continuity equation are reformulated into the tensor expressions, respectively. The element level evaluation phase is decomposed into the concatenated tensor contraction operations, which is implemented by the highly optimised arithmetic operation provided in Matlab. In contrast to the traditional implemented FEM, the tensor‐structured FEM has significantly improved the throughput and achieved high performance. The accuracy and efficiency of the tensor‐based algorithm are verified under the unipolar and bipolar model, respectively. The tensor‐based algorithm provides one order of magnitude speedup over the traditional algorithm in the elemental evaluation phase. ‘Tensorization’ is an efficient way to bridge the algorithm and the hardware.

Ashwini K. Arya, Soyul Han, Sanghoek Kim

This paper presents a review of the state-of-the-art antennas for the railway communications. There are various aspects that one should consider when designing an antenna, such as antenna size and directivity. While size constraints on railway antennas are not as critical as for mobile consumer counterparts, a radome structure is required to cover the antenna to minimize the aerodynamic resistance antenna. This paper reviews aerodynamic simulations to account for the drag coefficient of the antenna. In a low-frequency band (<5 GHz), railway antennas used to be omnidirectional in the horizontal plane. As the communication scheme advances toward 5G technology, high directivity is required for the railway antenna to compensate for the high path loss at high-frequency bands, i.e., 28-GHz band. We review recent studies of railway antennas over various frequency bands, such as LTE-R, LTE, and the lower and upper 5G bands. To accommodate multiple frequency bands with a single antenna, along with the aerodynamic radome cover, design techniques allowing multiple frequency bands are reviewed in this paper.

Nihad Abuawwad, Manuel dos Santos Dias, Hazem Abusara et al.

The emergence of topological magnetism in two-dimensional (2D) van der Waals (vdW) magnetic materials promoted 2D heterostructures as key building-blocks of devices for information technology based on topological concepts. Here, we demonstrate the all-electric switching of the topological nature of individual magnetic objects emerging in 2D vdW heterobillayers. We show from the first principles that an external electric field modifies the vdW gap between CrTe $_2$ and (Rh, Ti)Te$_2$ layers and alters the underlying magnetic interactions. This enables switching between ferromagnetic skyrmions and meron pairs in the CrTe$_2$/RhTe$_2$ heterobilayer while it enhances the stability of frustrated antiferromagnetic merons in the CrTe$_2$/TiTe$_2$ heterobilayer. We envision that the electrical engineering of distinct topological magnetic solitons in a single device could pave the way for novel energy-efficient mechanisms to store and transmit information with applications in spintronics.

S. Piltyay, A. Bulashenko, Y. Kalinichenko et al.

Modern wireless networks, stationary terrestrial and satellite systems use many modern technologies to increase communication channels information capacity. They save limited frequency resources. In satellite communications the polarization signal processing is applied to reuse the allocated frequency bands. Usage of circularly polarized electromagnetic waves, which transmit useful signals, reduces fading effects and eliminates disadvantages introduced by multipath propagation interferences. In this case the distortion levels for signals with an odd number of electromagnetic waves reflections in the receiving antenna systems will be reduced down to the thresholds of their cross-polarization isolation. Besides, in the case of orthogonal polarizations usage, the achieved information capacity of the applied wireless communication channel multiples almost by the factor of two. The type of polarization of the used electromagnetic wave strongly determinates the peculiarities of the process of its propagation in the space or transmission line. Polarization signal processing is frequently carried out in horn feed systems of the reflector antennas. Such feed networks and systems allow to transmit and receive signals with several kinds of polarization at the same time. The fundamental element of dual circular polarization antenna feed networks is a waveguide polarization duplexer. The phase, isolation and matching characteristics of a polarization converter strongly influence on the functionality and polarization discrimination possibilities of the entire reflector antenna system. Therefore, the development and optimization of the characteristics of waveguide polarizers for satellite communication antennas is a crucial technical problem, which must be solved by fast and accurate methods. The comparison of electromagnetic performance of waveguide polarizers with sizes obtained using a fast single-mode technique and by more accurate trust region optimization method is carried out in this research. The results for differential phase shift, level of voltage standing wave ratio, ellipticity coefficient and cross-polarization discrimination are shown and discussed.

Yu Feng, Wenxin Tang, Yue Zhang et al.

Abstract Film dielectric capacitors have been widely used in high‐power electronic equipment. The design of microstructure and the choice of fillers play an important role in nanocomposites' energy storage density. Machine learning methods can classify and summarise the limited data and then explore the promising composite structure. In this work, a dataset has been established, which contained a large amount of data on the maximum energy storage density of nanocomposites. Though using processed visual image information to express the internal information of composite, the prediction accuracy of the prediction models built by three machine learning algorithms increase from 84.1% to 91.9%, 80.9% to 68.9%, 70.6% to 81.6%, respectively. By calculating the branch weight in the random forest prediction model, the influence degree of different descriptors on the energy storage performance of nanocomposites is analysed. A total of 10 groups of composites with different structure and filler amount were prepared in the laboratory, which were used to verify the reliability of prediction models. Finally, the effective filler's structure is explored by three prediction models and some suggestions for the interface design of filler are given.

Yifan SONG, He ZHAO, Junyan SHEN et al.

The allowable harmonic current limits injected to the common connection points are stipulated for users respectively by GB/T 14549—93 and IEEE std.519:2014. However, there are some differences between two standards in determination methods and engineering application. The harmonics national standard GB/T 14549 under revision intends to adopt the emission limits of harmonic current for single user in IEEE std.519:2014. Therefore, it is necessary to fully discuss the rationality of the methods for determining the harmonic current limits. In this paper, the limits of the harmonic current in two standards are introduced, and their determination methods are deduced and discussed respectively. Finally, the similarities and differences between them are analyzed through case study.

Vasil Tabatadze, Kamil Karaçuha, Ömer Faruk Alperen et al.

Abstract The study investigates the H‐polarized plane wave diffraction by a slotted cylinder with different surface impedances employing an analytical‐numerical approach. The solution is obtained by expressing the current distribution on the obstacle with Gegenbauer polynomials considering the edge conditions. To obtain the field and current distribution on the surface, the Leontovich boundary condition on each side of the slotted cylinder is employed. The results are compared with Dirichlet and Neumann boundary condition cases obtained previously. It is observed that the resonant field amplitudes and the location at the resonances strongly depend on the impedance values.

Honglei Wang, Yingda Ren

Abstract Wireless data transmission near the sea surface can be realized by electromagnetic (EM) waves. The transmitting antenna is one of the most important parts of the EM communication system. The optimal antenna form can greatly improve communication performance. In this work, theoretical and experimental studies were presented for analysing the communication performance of magnetic dipoles near the sea surface. The influence of the seabed on the EM waves propagation near the sea surface was analysed. The model based on vector potential was built to study the radiation of magnetic dipoles in three‐layered conducting media. The experiments on the sea were conducted to comprehensively verify the EM waves propagation from seawater to seawater, seawater to air, air to air, and air to seawater. The good agreement of the theoretical and experimental results indicates that the performance of a horizontal magnetic dipole is superior to that of a vertical magnetic dipole in both‐way communications between seawater and air. The studies in this work are helpful for antenna design and system development in wireless data transmission near the sea surface.

Vyacheslav Klyukhin, Benoit Curé, Nicola Amapane et al.

The principal difficulty in large magnetic systems having an extensive flux return yoke is to characterize the magnetic flux distribution in the yoke steel blocks. Continuous measurements of the magnetic flux density in the return yoke are not possible and the usual practice uses software modelling of the magnetic system with special 3D computer programs. The flux return yoke of the Compact Muon Solenoid (CMS) magnet encloses a 3.8 T superconducting solenoid with a 6-m-diameter by 12.5-m-length free bore and consists of five dodecagonal three-layered barrel wheels around the coil and four endcap disks at each end. The yoke steel blocks serve as the absorber plates of the muon detection system. A TOSCA 3D model of the CMS magnet has been developed to describe the magnetic field outside of the solenoid volume, which was measured with a field-mapping machine. To verify the magnetic flux distribution calculated in the yoke steel blocks, direct measurements of the magnetic flux density with 22 flux loops installed in selected regions of the yoke were performed during the CMS magnet test in 2006 when four "fast" discharges of the CMS coil were triggered manually to test the magnet protection system. No fast discharge of the CMS magnet from its operational current of 18.2 kA, which corresponds to a central magnetic flux density of 3.8 T, has been performed that time. For the first time, in this paper we present measurements of the magnetic flux density in the steel blocks of the return yoke based on the several standard linear discharges of the CMS magnet from the operational magnet current of 18.2 kA. To provide these measurements, the voltages induced in the flux loops have been measured with six 16-bit DAQ modules and integrated offline over time. The results of the measurements during magnet linear ramps performed with a current rate as low as 1-1.5 A/s are presented and discussed.

Ramanand Sagar Sangam, Rakhesh Singh Kshetrimayum

Abstract Two bandpass filters based on hybrid spoof surface plasmon polariton (SSPP) and substrate integrated waveguide (SIW) are presented for X‐band applications, herein. The dispersion and transmission characteristics of the proposed hybrid SSPP‐SIW structures are analysed, and the influence on the variation of their structural parameters is investigated. The proposed dumbbell‐shaped SSPP shows more slow‐wave effects than the rectangle‐shaped SSPP for the same height of grooves, and hence could be a good choice in the design of compact, low loss and highly integrated microwave and terahertz devices. The lower and upper cut‐off frequencies of hybrid SSPP‐SIW bandpass filters can be adjusted independently by varying the structural parameters of SIW and SSPP units, respectively. The proposed two filters exhibit excellent passband (8–13.15 GHz for filter I and 8–13.5 GHz for filter II) and wide upper‐band rejection (>42.5 dB from 14.1 to 20 GHz for filter I and >41 dB from 14.2 to 19.5 GHz for filter II) simultaneously. Their size is very compact, amounts to only about 1λg × 0.7λg, where λg is the guided wavelength in the SIW at the centre frequency.

Wentao MA, Jinmei WANG, Yongqi WANG

Using virtual impedance technology to optimize the double closed-loop control structure can improve the equivalent output impedance of the inverter to be inductive and enhance the accuracy of power distribution by traditional inductive droop control strategies in low-voltage micro-grids, thus inhibiting circulating current. This approach, however, tends to overlook the impact of virtual impedance on system stability. In this regard, the transfer function of a three-loop control structure is derived, which includes virtual impedance, line impedance and common point voltage. A parallel model of inverters with different voltage levels is built, considering virtual complex impedance, and the model is simplified with the Thevenin’s equivalent. According to the Nyquist stability criterion, the effect of virtual impedance on system stability is analyzed under various operating conditions. The results show that the multi-inverter parallel system can maintain stable operation after the virtual impedance is added.

Patrick Wintzek, Shawki Alsayed Ali, Markus Zdrallek et al.

In contrast to rural distribution grids, which are mostly “feed-in oriented” in terms of electrical power, urban distribution grids are “load oriented”, as the number of customer connections and density of loads in urban areas is significantly higher than in rural areas. Taking into account the progressive electrification of the transport and heating sector, it is necessary to assess the required grid optimization or expansion measures from a conventional, as well as an innovative point of view. This is necessary in order to be able to contain the enormous investment volumes needed for transforming the energy system and aligning the infrastructures to their future requirements in time. Therefore, this article first explains the methodological approach of allocating scenarios of the development of electric mobility and heat pumps to analyzed grids. The article continues with describing which power values need to be applied and which conventional and innovative planning measures are available for avoiding voltage band violations and equipment overloads within the framework of strategic grid planning. Subsequently, the results of grid planning studies are outlined and evaluated with an assessment model that evaluates capital as well as operational costs. On this basis, planning and operation guidelines for urban low-voltage grids are derived. The main result is that low-voltage grids can accommodate charging infrastructure for electric mobility, as well as heat pumps to a certain degree. In addition, it is concluded that conventional planning measures are not completely avoidable, but can be partially avoided or deferred through dynamic load management.