Hasil untuk "Electricity and magnetism"

GUAN Yao, FENG Jin, WANG Qinghui et al.

In the evaluation of low-porosity and low-permeability light oil reservoirs in the eastern South China Sea using nuclear magnetic resonance(NMR) logging data, the permeability values tend to be overestimated. To improve the accuracy of NMR-derived permeability calculations, it is essential to thoroughly analyze the causes of this overestimation and establish corresponding correction methods. This paper systematically conducted NMR transverse relaxation time (T2) spectroscopy experiments under different saturation states, including water-saturated, bound water, oil-saturated, and residual oil states. By comparing the T2 spectra of the same core sample under water-saturated and oil-containing states, it was observed that light crude oil causes a significant rightward shift in the distribution of macropores within the T2 spectrum, while the distribution of micropores remains largely unchanged. This indicates that light oil is the primary cause of T2 spectrum anomalies and NMR permeability deviations. Based on this finding, T2 cutoff values for different reservoir types were determined through core classification, and a T2 spectrum correction method calibrated for macropore components was established. Results demonstrate that this method effectively corrects T2 spectra from light oil-bearing reservoirs to fully water-saturated state, significantly enhancing the accuracy of NMR-derived permeability measurements.

Muhammad Uzair, Guillaume François, Dirk Heberling et al.

ABSTRACT This study presents the design, characterisation and prototyping of a novel all‐dielectric artificial magnetic conductor (AMC) operating at 77 GHz. Unlike traditional metallic or hybrid counterparts, the proposed AMC is fabricated entirely from a commercial dielectric substrate, offering a low‐loss and low‐profile solution ideal for integration into compact antenna systems. The proposed AMC demonstrates strong reflection magnitude and achieves a 0° reflection phase at the targeted operating frequency. The −1‐dB reflection bandwidth is 3.6 and 8.2 GHz for ± 45° and ± 90° phase windows, respectively. Integration with a dipole antenna confirms that the AMC maintains reflection phase stability under placement and fabrication tolerances. Measured results using a commercial material characterisation kit align closely with simulations, with deviations primarily attributed to substrate anisotropy at 77 GHz. Additionally, two alternative all‐dielectric reflectors with high reflection magnitudes and nonzero reflection phases at 77 GHz are presented to support broader millimetre wave scenarios where in‐phase reflection is nonessential. This work is among the first to report an all‐dielectric AMC operating at millimetre wave frequencies while providing experimental validation, insights into anisotropy effects, fabrication constraints and real‐world integration.

Jingwei Wang, Zhanwen Wang, Lida Liu et al.

We revisit finite element method of modeling multi-scale photonic/electromagnetic devices via the proposed beam basis function, in combination with domain decompositions. Our approach ensures mathematical and physical consistency, can also handle multi-scale computational tasks efficiently with the assistance of the damping block-Jacobi iterative solver. By implementing the first-order Robin transmission condition at the interfaces between neighboring subdomains and introducing the dual “current” variables, we can significantly reduce the computational burden and communication data volume during the iterative solving process. The theoretical foundation and detailed implementation procedures are presented, accompanied with two representative examples. The first example is a refractive-diffractive hybrid optical system with feature size contrast up to 104, while the second example is the free surface optical system wherein the geometric ray tracing algorithm is inadequate. The obtained results for the two examples show excellent agreement with the standard finite element method (standard FEM) with significantly reducing the number of meshes required for computation and memory usages to nearly one-fifth. Since the computational time is inversely proportional to the number of decomposed subdomains (N) under the parallel computing configuration, the computational time in our work is approximately reduced to \begin{document}${1}/{3N}$\end{document} of that using standard FEM for the two examples.

G. Saxena, U. Gupta, S. Shukla et al.

A quad-element super-wideband (2-20GHz) MIMO antenna including dual notched-band response at WiMAX (3.30-3.70GHz) and satellite-band (6.99-8.09GHz) is designed on RO3035 with total dimension of 118mm×86mm×1.67mm. Unique decoupling structure has been deployed to enhance the isolation (˃20dB) between two antenna elements. The fundamental properties of MIMO antennas like bandwidth ratio (10:1), isolation (>18dB), gain (4.14dB), Envelop Correlation-Coefficient (<0.0065), Total Active Reflection-Coefficient (< 0dB), Channel Capacity Loss (<0.25bps/Hz) and radiation patterns are also investigated in order to determine their practicality. Measurement and simulation results of the proposed SWB-MIMO antenna from 2 to 20GHz indicate that it will be the suitable candidate for wireless and biomedical applications.

E. Mazzucato

Since a fusion reactor using the Deuterium-Tritium fuel cycle cannot be a source of clean energy because of the deleterious effects of energetic neutrons carrying 80% of the energy output, and it is very doubtful that it will be able to achieve Tritium self-sufficiency because of an extremely problematic and still unproven breeding procedure, this paper proposes a new reactor scheme capable of confining hot and dense plasmas using the Deuterium – Helium-3 fuel cycle. Such a reactor must be considered a source of clean energy because of its very low level of neutrons production, and its fuel is available in large quantity since we can get the needed Deuterium from seawater and likewise Helium-3 from the moon, as it was found from the samples of lunar soil brought back by the astronauts of the Apollo Mission. The proposed reactor consists of two 100 m long cylindrical plasmas, connected by semicircular sections to form a racetrack configuration. It should be capable of producing from 16 to 20 GW of fusion power when operating with an electron density of 3 × 1020 m−3, a magnetic field of 10 T and average temperatures from 40 to 45 keV. Out of this power, up to 10 GW will be used for replacing the loss of electron energy from bremsstrahlung radiation, with a consequent reduction in the reactor power output. However, such a loss could be mitigated by a partial recovery of the energy plasma radiation.

Pu ZHAO, Man ZHOU, Jianyu GAO et al.

According to the multi-energy coupling characteristics of the park-level integrated energy system (IES), the influencing factors of the IES construction are analyzed. Considering the positive impact of electric power substitution, an index system is built with such indexes as social benefits, energy utilization efficiency, reliability, economy and environmental protection, and a quantification model and calculation method for the indexes are proposed as well. A comprehensive evaluation method is proposed using combination weighting method to optimize the matter element extension model, in which the combination weighting method is used to integrate the subjective and objective weights according to the theory of minimum weight deviation vector, and the obtained expected combination weights are applied to the matter-element extension model to give the evaluation grades of the construction schemes. The case study has verified the scientificity and rationality of the proposed evaluation method, and demonstrated the positive effects of electric power substitution equipment on the construction of the park-level IES.

Yongliang ZHAO, Xin FU, Yang GUO et al.

The power accessories have various types and models, and the storage and retrieval management with RFID technology cannot cover them all, which often leads to the inaccuracy and low efficiency of power accessories storage and retrieval, and the management quality not to meet the production requirements. In view of these problems, we carry out a research on intelligent recognition of power accessories based on machine learning and image recognition to correct the deficiency of RFID technology for storage and retrieval management of power accessories. Firstly, the gray-scale processing and binarization methods are used to process the original images, and the minimum circumscribed rectangle is used to correct the original images. Secondly, a deep learning model suitable for identifying power accessories is constructed using CNN and CRNN deep neural networks with combination of CTC loss function, and the suspected accessories are recommended synchronously according to the image recognition coincidence. The images of power accessories are acquired by intelligent equipment, and their name and model are identified in real time using the proposed methods, with prompt of their overall dimension, application scope and product use. The experimental results show that the accuracy of the intelligent recognition of power accessories based on machine learning and image recognition reaches 95%, which significantly improves the intelligent level of warehousing management.

Kai ZHU, Yuqun FANG, Guangkai YU

In view of the problem that the test voltage of live working insulation tools for 1 000 kV UHV AC transmission lines is too high, causing abnormal damage to the work tools, we made an in-depth analysis of the power frequency and operating overvoltage level for the live working condition of 1 000 kV AC transmission lines. And at the same time, a research was carried out on the voltage selection and safety margin for the 1 000 kV UHV live working insulation tool test. After comprehensive analysis, the reasonable test voltage and safety margin range are put forward, and the proposed revision values are verified by a number of tests including power frequency withstand voltage test, insulation material electrical performance test and live working safety test, which have fully proved the rationality of the proposed revision values.

Muchen DAI, Xiangguang LENG, Boli XIONG et al.

Sea–land segmentation is a basic step in coastline extraction and nearshore target detection. Because of poor segmentation accuracy and complicated parameter adjustment, the traditional sea–land segmentation algorithm is difficult to adapt in practical applications. Convolutional neural networks, which can extract multiple hierarchical features of images, can be used as an alternative technical approach for sea–land segmentation tasks. Among them, BiSeNet exhibits good performance in the semantic segmentation of natural scene images and effectively balances segmentation accuracy and speed. However, for the sea–land segmentation of SAR images, BiSeNet cannot extract the contextual semantic and spatial information of SAR images; thus, the segmentation effect is poor. To address the aforementioned problem, this study reduced the number of convolution layers in the spatial path to reduce the loss of spatial information and selected the ResNet18 lightweight model as the backbone network for the context path to reduce the overfitting phenomenon and provide a broad receptive field. At the same time, strategies for edge enhancement and loss function are proposed to improve the segmentation performance of the network in the land and sea boundary region. Experimental results based on GF3 data showed that the proposed method effectively improves the prediction accuracy and segmentation rate of the network. The segmentation accuracy and F1 score of the proposed method are 0.9889 and 0.9915, respectively, and the processing rate of SAR image slices with the resolution of 1024 × 1024 is 12.7 frames/s, which are better than those of other state-of-the-art approaches. Moreover, the size of the network is more than half of that of BiSeNet and smaller than that of U-Net. Thus, the network exhibits strong generalization performance.

Yawei Wang, Hongyu Bai, Jianwei Li et al.

Second generation (2G) high-temperature superconductor (HTS) (RE)Ba(2)Cu(3)O(x) (REBCO) shows a great potential in building high field magnets beyond 23.5 T. The electromagnetic modelling is vital for the design of HTS magnet, however, this always suffers the challenge of huge computation for high field magnets with large number of turns. This study presents a novel electromagnetic modelling based on T-A formulation for REBCO magnets with thousands of turns. An equivalent turn method is proposed to reduce the number of turns in calculation, so that the computation cost can be reduced significantly, and meanwhile the key electromagnetic behaviour of HTS magnet can be simulated with enough accuracy. The ramping operation of a fully HTS magnet with 12,000 turns are analysed using both the original T-A model with actual turns and improved T-A model with equivalent turns. The two models show a good agreement on the key electromagnetic behaviours of the magnet: distribution of current density, magnetic fields, screen current induced field and magnetisation loss, so that this improved T-A model using equivalent turns is validated. The T-A modelling of REBCO magnet is a powerful tool for the electromagnetic analysis of industry-scale high field magnets.

Kuayu WU, Jiancheng ZHANG, Long WU et al.

Based on the development trend of the next generation power system, a novel flexible excitation system is designed based on three-level voltage source converter, and a matching five-level DC chopping circuit is proposed. An analysis is made of the controlling mode and performance of two DC chopping circuits with excitation current 6-IGBT or 3-IGBT. A simulation model of flexible excitation system is built based on PSCAD. The feasibility of the flexible excitation system with proposed five-level chopping topology and the control performance advantage over conventional self-shunt excitation are analyzed and verified.

LIU Wen-qing, SONG Yan-hong, WANG Xue-lu et al.

The reaction of photocatalytic methanol reforming in a real solid-liquid reaction environment was studied by in operando nuclear magnetic resonance (NMR) spectroscopy. Four liquid-state intermediate products were detected in the reaction systems investigated, including HOCH2OH, CH3OCH2OH, HCOOH and HCOOCH3. It was also demonstrated that the crystal types of TiO2 catalysts had a strong influence on the production of the four intermediate products. And the contents of the four products increased with the increasing illumination time. Palladium (Pd) loading enhanced the production of CH3OCH2OH and HOCH2OH by 2~3 orders of magnitude, but had little effects on the production of HCOOCH3 and HCOOH.

S. Bankov, A. Davydov, V. Kalinichev et al.

A two-function filtering antenna device in the 1-2 GHz band is investigated. The device radiates or receives electromagnetic waves of circular polarization and simultaneously performs the function of a second-order bandpass filter. The considered design consists of a dual-mode printed antenna-resonator coupled with two non-radiating resonators which are fed by a quadrature balanced power divider. Using the model in the form of an equivalent circuit the main features of the structure synthesis and its tuning are analyzed including potentially achievable characteristics. The results of the numerical simulations using electromagnetic software are presented in comparison with the experimental characteristics for the prototype made of high-permittivity high-quality ceramics. It is found that the proposed design is characterized by an almost two-fold increase of the operating frequency band compared to the resonant antenna itself while maintaining a low level of cross-polarization within the passband. It is also shown that the design has the frequency response of the second-order bandpass filter.

Bu Yuncheng, Wang Yu, Zhang Fubo et al.

The array InSAR system obtains a three-dimensional image of an observed scene using a combination of pulse compression and synthetic and real aperture techniques. However, Antenna Phase Center (APC) errors can occur within a practical array InSAR system, which thus degrades the imaging quality in a height direction. The aim of this paper is to improve calibration problems occurring with APC errors. The effect of APC errors is analyzed, and a calibration method based on the orthogonal subspace principle is proposed that utilizes SAR Single Look Complex (SLC) to obtain the noise subspace through eigenvalue decomposition. The subspace orthogonal principle is then used to solve the APC positions of multiple channels simultaneously. In addition, a calibration scheme for the APC position is presented for application with an array InSAR system. The effectiveness of the proposed calibration method is verified using simulations and experimental results.

Wenxia Sima, Potao Sun, Ming Yang et al.

At present, the insulation performances of electrical apparatus under lightning impulse voltages are always evaluated by the withstand test of standard lightning impulse voltage (1.2/50 µs), which is recommended by IEC Standard. However, the actual time parameters of transformer invading lightning impulse voltage present an obvious dispersibility characteristics. The standard wave shape is only representative of one particular class of lightning waves, which is far from satisfactory to act as the guidance waveform in the design of power equipment insulation. On the basis of the above research background, the relationship between breakdown characteristics of oil paper insulation and time parameters of applied lightning impulse voltage was investigated in this study. The 50% breakdown voltage characteristics of oil paper insulation under lightning impulse voltage with different time parameters were determined. The test results indicate that a short wave front time could lead to relatively low 50% breakdown voltage, while when the wave tail time varied, the 50% breakdown voltage of oil paper insulation barely changed. At last the simulation model of oil paper insulation was developed, and the current flowing through the oil paper insulating system under lightning impulse voltage was calculated. On the basis of the simulating results, the relationship between current and time parameters was analysed.

Zhang Zhe, Zhang Bingchen, Hong Wen et al.

Sparse microwave imaging is new concept, theory and methodology of microwave imaging, which introduces the sparse signal processing theory to microwave imaging and combines them together to overcome the paradox of increasing system complexity and imaging performance of current Synthetic Aperture Radar (SAR) systems. Traditional airborne SAR systems are facing a phase error problem in the echo which is caused by the non-ideal motion of the aircraft. This phase error could be compensated by autofocus algorithms. But in the sparse microwave imaging, such autofocus algorithm are no longer valid because traditional signal processing based on matched filtering has been replaced with sparse reconstruction. Current autofocus algorithms under sparse constraints are usually based on a two-step iteration, which convergences slowly and costs plenty of computation. In this paper, we introduce the Map-Drift (MD) autofocus algorithm to the accelerated sparse microwave imaging algorithm based on SAR raw data simulator, and propose the novel “MD-SAR raw data simulator autofocus algorithm”. This algorithm keeps the advantages of both accelerated imaging algorithm and MD algorithm, including the fast convergence and accurate compensation of two-order phase error in echo. Compared with current algorithms based on two-step iteration, the propose method convergences fast and effectively.

P. Manfredi, F. Canavero

Cable bundles often exhibit random parameter variations due to uncertain or uncontrollable physical properties and wire positioning. Efficient tools, based on the so-called polynomial chaos, exist to rapidly assess the impact of such variations on the per-unit-length capacitance and inductance matrices, and on the pertinent cable response. Nevertheless, the state-of-the-art method for the statistical extraction of the per-unit-length capacitance and inductance matrices of cables suffers from several inefficiencies that hinder its applicability to large problems, in terms of number of random parameters and/or conductors. This paper presents an improved methodology that overcomes the aforementioned limitations by exploiting a recently-published, alternative approach to generate the pertinent polynomial chaos system of equations. A sparse and decoupled system is obtained that provides remarkable benefits in terms of speed, memory consumption and problem size that can be dealt with. The technique is thoroughly validated through the statistical analysis of two canonical structures, i.e. a ribbon cable and a shielded cable with random geometry and position.

Xiang Yin, Zhang Kai, Hu Cheng

Radar Automatic Target Recognition (RATR) is the key technique to be breaked through in the fuure development of intelligent weapon system. Compared to the 2-D SAR image target recognition, High Resolution Range Profile (HRRP) target recognition has the advantage of low data dimension, low requirement of radar system's calculation and storage ability, and the imaging algorithm is also not complicated. HRRP imaging is the first and the key process in target recognition, its speed and imaging quality can directly influence the real-time capability and accuracy of target recognition. In this paper a new HRRP imaging algorithm — NUFFT algorithm is proposed, the derivation of mathematical expression is given, both for the echo simulation process and the imaging process. In the meantime, by analyzing each step's calculation complexity, we compared the calculation complexity of four different imaging algorithms, we also simulate two target's imaging and target recognition processing. Theoretical analysis and simulation both prove that the proposed algorithm's calculation complexity is improved in various degree compared with the others, thus can be effectively used in target recognition.

Kelly Miller, Nathaniel Lasry, Kelvin Chu et al.

Previous research suggests that students’ prior knowledge can interfere with how they observe and remember lecture demonstrations. We measured students’ prior knowledge in introductory mechanics and electricity and magnetism at two large universities. Students were then asked to predict the outcome of lecture demonstrations. We compare students’ predictions before having seen the demonstration to what they report having seen both right after the demonstration and several weeks later. We report four main findings. First, roughly one out of every five observations of a demonstration is inconsistent with the actual outcome. Second, students who understand the underlying concepts before observing the demonstration are more likely to observe it and remember it correctly. Third, students are roughly 20% (23%) more likely to observe a demonstration correctly if they predict the outcome first, regardless of whether the prediction is correct or not. Last, conceptual learning is contingent on the student making a correct observation. This study represents an initial step towards understanding the disconnect reported between demonstrations and student learning.

Homeyra R. Sadaghiani

We have been piloting web-based multimedia learning modules (MLMs), developed by the Physics Education Research Group at the University of Illinois at Urbana Champaign (UIUC), as a “prelecture assignment” in several introductory physics courses at California State Polytechnic University at Pomona. In this study, we report the results from a controlled study utilizing modules on electricity and magnetism as a part of a blended hybrid-online course. We asked students in the experimental section to view the MLMs prior to attending the face-to-face class, and to make sure this would not result in additional instructional time, we reduced the weekly class time by one-third. We found that despite reduced class time, student-learning outcomes were not hindered; in fact, the implementation of the UIUC MLMs resulted in a positive effect on student performance on conceptual tests and classroom discussion questions.