Hasil untuk "Electricity and magnetism"

Yudi Yang, Zhuang Qian, Ruichun Xiao et al.

We identify hexagonal YMnO$_3$ as a material realization of the elusive $β$-phase of unconventional magnetism, a noncollinear, noncoplanar antiferromagnetic state defined by intrinsic spin-momentum locking and a topological spin texture. First-principle calculations reveal that this unique electronic structure enables a perpendicular electric field to generate a transverse pure spin current, a response that occurs without requiring relativistic spin-orbit coupling. Symmetry analysis demonstrates that this spin current is intimately related to the material's ferroelectric polarization that breaks the inversion symmetry and is rigorously forbidden at domain walls where electrical polarization vanishes. This provides a blueprint for a non-volatile transistor where a gate voltage switches the spin current conductivity by controlling domain wall density, enabling all-electrical control for energy-efficient antiferromagnetic spintronics.

William Reed Kendrick, Benoit Forget

Multiphysics analysis has become a common technique for nuclear reactor design validation, with neutronic-thermal analysis being the typical choice for understanding reactor dynamics. The concept of adding mechanical simulation such as thermal expansion to this coupling is still relatively new, however, and presents many computational challenges. While large reactors see relatively little neutronic impact from thermal expansion and may not warrant the challenge of undertaking this level of coupling, recent studies of microreactor geometries show that smaller reactors see larger impacts from thermal expansion. This work performs coupled neutronic-thermal-mechanical simulation of the Kilowatt Reactor Using Stirling TechnologY (KRUSTY) using OpenMC and Multiphysics Object-Oriented Simulation Environment in order to analyze the neutronic and thermal impact of including thermal expansion at steady state. The results show that while thermal expansion has a significant effect on global neutronic tallies, it has relatively minor impact on spatial heating rates or temperatures in the system. This remains true even when simulating a multiple heat pipe failure scenario to introduce thermal asymmetry.

TANG Shihao, YANG Jinyu, XU Yajie et al.

Signal-to-noise ratio (SNR) is a key parameter governing signal quality in benchtop MRS spectrometers, where quadrature circularly polarized coils offer an effective means to enhance SNR. However, the confined space within the compact magnets of desktop systems poses challenges for implementing such coils—a strategy previously unattempted in this domain. Leveraging a self-developed desktop MRS platform, this study designed and fabricated a flexible printed circuit-based transceiver-integrated circularly polarized coil system, comprising orthogonally arranged saddle and Helmholtz coils. The coil geometry was optimized through Ansys Maxwell simulations, and experimental validation using CuSO₄ solution demonstrated SNR improvements of 28.78% and 29.21% over single-channel saddle and Helmholtz coils, respectively, alongside a 37.5% reduction in reflected power. These results confirm the viability of circularly polarized coils for advancing desktop MRS probe performance.

Ming REN, Qianyu LI, Changjie XIA et al.

The timely and accurate online estimation for composite insulators of transmission lines can effectively prevent pollution flashover accidents. A visualized estimation method of composite insulator pollution status of transmission line was proposed in this paper. Firstly, a semi-automatic registration method for multisource reflective spectral images was constructed by combining image registration algorithm and target area selection, which solved the inherent image registration problem of multi-lens camera. Secondly, model pre-training was conducted through shooting artificial contaminated samples using the low cost, lightweight, and high imaging quality multi-lens multispectral imaging equipment, and further transfer training was conducted through real natural contaminated samples to construct a pollution grade diagnosis model of composite insulation material surfaces. Finally, the actual pollution status of transmission line composite insulators was measured and analyzed under different shooting conditions using the unmanned aerial vehicle platform. The results indicate that the pollution grade classification accuracy for artificial and natural contaminated samples is 95.3% and 87.8%, respectively, and the pollution grade classification accuracy for actual transmission line composite insulators can reach up to 90% with pollution distribution area clearly displayed. The feasibility of transmission line insulator pollution grade estimation and pollution distribution visualization diagnosis based on reflective multispectral imaging technology is verified, which can provide a new technique for status inspection and maintenance decision of transmission line insulators.

Xuan Li, Jiang Guo, Jiangang Bi et al.

Abstract To address the lack of voltage ratio standards for accuracy testing of low‐frequency voltage transformers, it is necessary to develop a 3 kV low‐frequency induction voltage divider. Firstly, based on the analysis of the error sources of the induction voltage divider, a method was proposed to calculate the excitation impedance of the induction voltage divider using complex magnetic permeability. A measurement circuit based on the lock‐in principle was set up to measure the complex magnetic permeability of grained‐oriented silicon steel 30P100 and permalloy 1J85 at different frequencies. Secondly, a 3 kV low‐frequency induction voltage divider with a two‐stage excitation and a series‐wound ratio winding in 10 sections was designed. The errors of the two stages of the instrument transformers were calculated at 20 and 50 Hz, respectively. Finally, the divider's errors were calibrated at 20 and 50 Hz using the reference potential method. The results showed that, compared to 50 Hz, the excitation impedance of the two stages decreased and the errors increased at 20 Hz, with the overall error of the induction voltage divider being better at 50 Hz than at 20 Hz. Experimental measurements indicated that at 20 Hz, the ratio error and phase error of the 3 kV two‐stage excitation induction voltage divider were better than 1 × 10−5, whereas at 50 Hz, the errors were better than 1 × 10−6. This study provides support for the accuracy testing of voltage transformers used in low‐frequency flexible AC transmission projects.

Vera Shikhova, Andrey Akhmatkhanov, Maria Chuvakova et al.

In this paper, we present the electric field controllable diffractive optical elements in strontium–barium niobate single crystals with stable tailored spiral-shaped domain structure and demonstrate the generation of optical beam with orbital angular momentum. The required domain pattern was created in the sample with initial domain structure by electric field application using the photolithographically defined liquid electrode. A series of bipolar triangular electric field pulses were applied to the sample for determination of the optimal parameters for complete polarization switching under the electrode. The stable tailored domain pattern of the spiral shape was created by the application of the unipolar pulse of a special shape. The complete switching under the electrode and partial switching under the photoresist layer have been revealed. The imaging by Cherenkov-type second harmonic generation microscopy confirmed that the created domain structure reaches the opposite polar surface. The imaging of the diffraction pattern of the laser beam passing through a voltage-biased DOE confirmed the formation of the beam with orbital angular momentum. The half-wave voltages of 237[Formula: see text]V and 302[Formula: see text]V for wavelength 632.8[Formula: see text]nm and 532[Formula: see text]nm, respectively, for 2-mm-thick sample were measured. The obtained knowledge can be used for the development of domain engineering methods in strontium–barium niobate single crystals for the creation of tailored domain structures for manufacturing of electric field controllable diffractive optical elements.

Theodore Modis

The main advantage of electric vehicles, namely, their non-polluting operation, is compromised when the electricity they use comes from burning fossil fuels. The number of electric vehicles on the road is growing much faster than the amount of green electricity produced. It is forecasted that in 2037 the number of electric vehicles on the road will need an amount of electricity equal to the entire green electricity produced at that time. Therefore, green operation of electric vehicles entering the market after 2037 will be impossible. The sales of hydrogen-burning vehicles are poised to overtake the sales of electric vehicles in 2041, but a non-polluting overall operation for them is not guaranteed either at this time.

Myung-Geun Han, Joachim Dahl Thomsen, John P. Philbin et al.

Two-dimensional van der Waals magnets hosting topological magnetic textures, such as skyrmions, show promise for applications in spintronics and quantum computing. Electrical control of these topological spin textures would enable novel devices with enhanced performance and functionality. Here, using electron microscopy combined with in situ electric and magnetic biasing, we show that the skyrmion chirality, whether left-handed or right-handed, in insulating Cr2Ge2Te6, is controlled by external electric field direction applied during magnetic field cooling process. The electric-field-tuned chirality remains stable, even amid variations in magnetic and electric fields. Our theoretical investigation reveals that nonzero Dzyaloshinskii-Moriya interactions between the nearest neighbors, induced by the external electric field, change their sign upon reversing the electric field direction, thereby facilitating chirality selection. The electrical control of magnetic chirality demonstrated in this study can be extended to other non-metallic centrosymmetric skyrmion-hosting magnets, opening avenues for future device designs in topological spintronics and quantum computing.

Yuanyang Ren, Yang Wang, Qiankai Zhang et al.

Abstract The ionic transport process is an important counterpart to charge transport in oil‐paper insulation, and it significantly impacts oil flow electrification at the oil‐paper interface. Despite this, the dynamics of this phenomenon and the underlying mechanisms remain unclear, particularly at the molecular level. To understand this fundamental aspect, we conduct Molecular Dynamics study on the transport behaviour of an impurity ion in different oil‐paper insulation models under various external electric fields. Different influence factors, such as external electric fields, temperatures, and local structural characteristics, are investigated in relation to the corresponding ionic mobility in different polymer models. According to the simulations, ionic mobility and its response to electric fields are higher in weaker electrostatic models. As a result, mineral oil exhibits the highest ionic mobility and the most substantial enhancement of ionic mobility by external electric fields, followed by vegetable oil, oil‐paper blends, and insulating paper. This significant deviation in ionic mobility between oil and paper leads to the formation of an electric double layer near the oil‐paper interface. The underlying physical mechanisms of different ionic mobility and its response to the electric field in different polymer models could be explained by the different polymer structural influences in terms of interaction energy and coordination numbers in a static manner, as well as by the interactions between the impurity ion and its surrounding atoms in terms of lifetime correlation functions and velocity autocorrelation functions in a dynamic manner. In addition, the influence of temperature on ionic mobility in mineral and vegetable oil is examined, and their activation energies are calculated. Advancing in the fundamental understanding of the dynamics of the ion transport process in oil‐paper insulation is vital to improving their insulating properties for oil‐impregnated power transformers.

Edgar C. Buck, Dallas D. Reilly, Luke E. Sweet et al.

The degradation of the internal structure of plutonium (IV) oxalate during calcination was investigated with Transmission Electron Microscopy (TEM), electron diffraction, Electron Energy-Loss Spectroscopy (EELS), and 4D Scanning TEM (STEM). TEM lift-outs were prepared from samples that had been calcined at 300°C, 450°C, 650°C and 950°C. The resulting phase at all calcination temperatures was identified as PuO2 with electron diffraction. The grain size range was obtained with high-resolution TEM. In addition, 4D STEM images were analyzed to provide grain size distributions. In the 300°C calcined sample, the grains were <10 nm in diameter, at 650°C, the grains ranged from 10 to 20 nm, and by 950°C, the grains were 95–175 nm across. Using the Kolmogorov-Smirnov (K-S) two sample test, it was shown that morphological measurements obtained from 4D-STEM provided statistically significant distributions to distinguish samples at the different calcination conditions. Using STEM-EELS, carbon was shown to be present in the low temperature calcined samples associated with oxalate but had formed carbon (possibly graphite) deposits in the 950°C calcined sample. This work highlights the new methods of STEM-EELS and 4D-STEM for studying the internal structure of special nuclear materials (SNM).

Yipeng ZHANG, Dongdong LU, Xiaolan QIU et al.

With the widespread application of Synthetic Aperture Radar (SAR) images in ship detection and recognition, accurate and efficient ship classification has become an urgent issue that needs to be addressed. In few-shot learning, conventional methods often suffer from limited generalization capabilities. Herein, additional information and features are introduced to enhance the understanding and generalization capabilities of the model for targets. To address this challenge, this study proposes a few-shot ship classification method for SAR images based on scattering point topology and Dual-Branch Convolutional Neural Network (DB-CNN). First, a topology structure was constructed using scattering key points to characterize the structural and shape features of ship targets. Second, the Laplacian matrix of the topology structure was calculated to transform the topological relations between scattering points into a matrix form. Finally, the original image and Laplacian matrix were used as inputs to the DB-CNN for feature extraction. Regarding network architecture, a DB-CNN comprising two independent convolution branches was designed. These branches were tasked with processing visual and topological features, employing two cross-fusion attention modules to collaboratively merge features from both branches. This approach effectively integrates the topological relations of target scattering points into the automated learning process of the network, enhancing the generalization capabilities and enhancing the classification accuracy of the model. Experimental results demonstrated that the proposed approach obtained average accuracies of 53.80% and 73.00% in 1-shot and 5-shot tasks, respectively, on the OpenSARShip dataset. Similarly, on the FUSAR-Ship dataset, it achieved average accuracies of 54.44% and 71.36% in 1-shot and 5-shot tasks, respectively. In the case of both 1-shot and 5-shot tasks, the proposed approach outperformed the baseline by >15% in terms of accuracy, underscoring the effectiveness of incorporating scattering point topology in few-shot ship classification of SAR images.

Walter Schirmacher, Thomas Franosch, Marco Leonetti et al.

We consider Maxwell's equations in a 3-dimensional material, in which both, the electric permittivity, as well as the magnetic permeability, fluctuate in space. Differently from all previous treatments of the disordered electromagnetic problem, we transform Maxwell's equations and the electric and magnetic fields in such a way that the linear operator in the resulting secular equations is manifestly Hermitian, in order to deal with a proper eigenvalue problem. As an application of our general formalism, we use an appropriate version of the Coherent-Potential approximation (CPA) to calculate the photon density of states and scattering-mean-free path. Applying standard localization theory, we find that in the presence of both electric and magnetic disorder the spectral range of Anderson localization appears to be much larger than in the case of electric (or magnetic) disorder only. Our result could explain the absence of experimental evidence of 3D Anderson localization of light (all the existing experiments has been performed with electric disorder only) and pave the way towards a successful search of this, up to now, elusive phenomenon.

Xin REN, Du WANG, Yafei JIN et al.

A multi-objective optimization model for combined heat and power units is established to address the problem of difficulty in balancing energy consumption, economy and low carbon in the operation of the combined heat and power units. Firstly, combining with the power peaking auxiliary market and carbon emission trading market, and taking the efficiency, profit and carbon emission rate as the objective functions, the multi-objective particle swarm algorithm is used to find the best power generation power considering the constraints related to the unit operation. Then, the multi-objective decision making is performed by using the information entropy weight method combined with the technique for order preference by similarity to an ideal solution. Finally, it is verified by the unit simulation model. The results show that the optimized optimal power generation is 115.1, 89.5 and 89.1 MW for 20, 100 and 180 t/h steam supply, respectively, and the optimized operation scheme significantly reduces the carbon emission and takes into account the energy consumption, economy and low carbon performance of the unit.

Quan CHEN, Xuanjun ZONG, Mengyuan LI

The planning and operation of multi-heterogeneous energy systems often only considers a single optimization objective, which is not conducive to the balanced among economic operation, low carbon emission and energy conservation. This paper proposes a multi-dimensional objective collaborative optimization method that considers energy saving. Firstly, a multi-dimensional optimization objective is proposed with consideration of system economy, environmental protection and energy saving, and a multi-objective optimization model framework for multi-heterogeneous energy system is established by modeling energy conversion and distribution equipment in the system. Then, the NSGA-Ⅲ (non-dominated sorting genetic algorithm Ⅲ) is utilized to solve the multi-objective collaborative optimization model proposed in this paper, and the optimal feasible solution set (Pareto optimal solution set) is obtained. Finally, based on the simulation example, the effectiveness of the proposed method is verified through analysis of the optimal solution set and decision-maker preference. It is also demonstrated that considering the objective of energy conservation can avoid the system's excessive preference to consuming natural gas energy.

B. Ploss, D. Smykalla, S. Engel

Vinylidene fluoride-trifluoroethylene copolymer films of molar ratio 70/30 with thickness of about 1 [Formula: see text]m have been deposited from solution in ethyl methyl ketone to a glass substrate with an aluminum electrode by spin coating. The solution has been filtrated through a PTFE membrane filter with pore size 0.2 [Formula: see text]m directly before spin coating or it has been used as is (unfiltrated). After deposition of a top electrode, the samples have been polarized by hysteresis loops with an electric field amplitude of about 100 V/[Formula: see text]m. In samples, annealed at temperature 145[Formula: see text]C for 3 h, a high remanent polarization of about 7.5 [Formula: see text]C/cm2 has been achieved, without significant differences between samples fabricated of filtrated or unfiltrated solution. Spherulitic lamella are growing in films fabricated of filtrated solution when they are heated above the melting temperature to 159[Formula: see text]C for 3 min before the further annealing process at 145[Formula: see text]C. These films show substantially lower remanent polarization below 4 [Formula: see text]C/cm2. Pyroelectric images recorded with a pyroelectric laser scanning microscope show that the spherulites have very small pyroelectric activity, i.e., the spherulites consist of flat-on lamella. In contrast, no spherulitic lamella are growing in films fabricated of unfiltrated solution heated above the melting temperature, melted and annealed under the same conditions. An explanation for this observation is that filtrating changes the structure of the copolymer in solution from polymer coil to rod. Copolymer rods deposited on a substrate will crystallize in flat-on lamella when heated above the melting temperature, in contrast to copolymer coils which crystallize in edge-on lamella.

Lei WANG, Yibing LIU, Wei TENG et al.

In addition to withstanding aerodynamic forces, blades also experience other forces such as gravity and centrifugal force during operation, as well as damage from rain, snow, sand, salt spray, lightning and other factors, making the wind turbine blade structure and surface vulnerable. Failure to detect and repair such damage in a timely manner can lead to reduced power generation efficiency, downtime and even accidents. Therefore, damage detection of wind turbine blades is of great significance for ensuring the safe and efficient operation of wind turbines and reducing the cost of power generation over the life cycle of the system. This article provides a comprehensive review of the types and causes of wind turbine blade damage based on relevant literature from both Chinese and international sources. It also systematically introduces existing wind turbine blade damage detection technologies, categorizing them into real-time online monitoring and non-real-time detection, and compares the advantages and disadvantages of each technology. Finally, based on the actual engineering application of wind turbines and the development of non-destructive testing technology, the future development trend of non-destructive monitoring/detection technology for wind turbine blades is proposed.

Joanna Blawat, Madalynn Marshall, John Singleton et al.

Eu-based compounds often exhibit unusual magnetism, which is critical for nontrivial topological properties seen in materials such as EuCd2As2. We investigate the structure and physical properties of EuZn2As2 through measurements of the electrical resistivity, Hall effect, magnetization, and neutron diffraction. Our data show that EuZn2As2 orders antiferromagnetically with an A-type spin configuration below TN = 19 K. Surprisingly, there is strong evidence for dominant ferromagnetic fluctuations above TN, as reflected by positive Curie-Weiss temperature and extremely large negative magnetoresistance (MR) between TN and Tfl » 200 K. Furthermore, the angle dependence of the MRab indicates field-induced spin reorientation from the ab-plane to a direction approximately 45° from the ab plane. Compared to EuCd2As2, the doubled TN and Tfl make EuZn2As2 a better platform for exploring topological properties in both magnetic fluctuation (TN < T < Tfl) and ordered (T < TN) regimes.

Bang DU, Xiaolan QIU, Zhe ZHANG et al.

Synthetic Aperture Radar (SAR) Tomography (TomoSAR) is a novel technique that enables three-Dimensional (3-D) imaging using multi-baseline two-Dimensional (2-D) data. The essence of TomoSAR is actually to solve a one-dimensional spectral estimation problem. Compressed Sensing-based (CS) algorithm can retrieve solutions with only a few non-uniform acquisitions and has gradually become the main imaging method. In the conventional processing flow of CS algorithms, the continuous elevation direction is divided into a pre-set grid, and the targets are assumed to be exactly on the grid. \begin{document}$ {{L}}_{1} $\end{document} minimization has been proven to be effective in TomoSAR imaging. In the conventional processing flow, the continuous elevation axis is divided into fixed grids, and scatters are assumed to be exactly on the pre-set grid. However, this hypothesis is generally untenable, and will lead to a problem called “Basis Mismatch”, which is rarely discussed in TomoSAR. In this letter, we first discuss the model of Off-grid TomoSAR, and then propose an addictive perturbation model to compensate for the errors caused by the grid effect. We utilize the local optimization thresholding algorithm to solve the complex-valued \begin{document}$ {{L}}_{1} $\end{document} minimization problem of TomoSAR. We conducted experiments both on simulation data and actual airborne flight data. Our simulation results indicate that the proposed method can estimate a more accurate position of scatters, which leads to better original signal recovery. The reconstruction results of actual data verify that the impact of grid mismatch can be mostly eliminated.

Rangga Ade Julianto, Efrizon Efrizon, Hendrick Hendrick et al.

PCBs are very influential on the manufacture of electronic devices, for example when there is even a small number of PCB paths that are cut off or damaged, the electronic device cannot be operated properly. Therefore, in this study, the author tried to create and analyze a defect checking tool on PCBs to replace human vision to make it easier and can save costs. This tool is equipped with the help of a Logitech c920 Webcam and a Raspberry Pi 3b+ microprocessor which is used to store and run programs that have been created on Python programming software, so this tool can be used portablely. With these two technologies, Image Processing can be used to detect objects with the OpenCv library and Google Colab. PCB defect detection tool with the help of Image Processing uses yolo convolutional neural network method to help determine path damage on the PCB. You Only Look Once (YOLO) algorithm with five detection classifications, namely short, open circuit, missing hole, mouse bite, and spur. From the results of the study, the results were obtained that the YOLO algorithm was able to detect these five classifications with a value of mAP@0.5 short 90.67%, open circuit 97.86%, Mouse Bite 94.43%, Missing Hole 96.09%, and spur 97.56%.

Mihir Ranjan Sahoo, Saroj Kumar Nayak, Kalpataru Pradhan

Using density functional theory we show that the interaction between two Mn atoms can be tuned from anti-ferromagnetic (AFM) to ferromagnetic (FM) state by creating charge disproportion between the two on a 2D surface. The non-metallic planar heterostructures, the 2D surface, in our work is designed by doping carbon hexagon rings in a hexagonal boron nitride (h-BN) sheet. In addition, we show that an external electric field can be used to control the charge disproportion and hence the magnetism. In fact, our calculations demonstrate that the magnetic states of the dimer can be switched from AFM to FM or vice versa in an external electric field. The origin of this magnetic switching is explained using the charge transfer from (or to) the Mn dimer to (or from) the 2D material. The switching between anti-ferromagnetic to ferromagnetic states can be useful for future spintronic applications.