Hasil untuk "Electricity and magnetism"

Kashminder S. Mehta, Braden Goddard, Zeyun Wu

This study presents a multiphysics computational simulation framework for analyzing pebble dynamics and thermal-fluid behavior in High-Temperature Gas-Cooled Pebble Bed Reactors (HTG-PBR). The pebble circulation and intermixing effects are predicted using Discrete Element Method (DEM) implemented in LIGGGHTS, while the thermal-fluid behavior is simulated with computational fluid dynamics (CFD) in OpenFOAM. The CFD model employs a porous-media formulation with a local thermal non-equilibrium model to capture the energy exchange between the helium coolant and pebbles. Integrating the DEM-based mixing effects into the porous CFD model enables a more physically representative and scalable approach for full-core reactor analysis. Both DEM and CFD solvers are validated using established pebble-bed benchmark problems to confirm the viability of the developed computational models. A HTG-PBR-like conical model reactor is employed as a test problem to evaluate the developed method. The simulation results confirm the predictive capability of the developed models for HTG-PBR performance analysis and provide insight for future multiphysics coupling strategies for reactor design optimization.

Stefan Finsterle, Michael J. Hannon, Jesse Sloane

We propose, apply, and verify a screening approach for the selection of safety-relevant radionuclides that should be tracked in models assessing the performance of geologic repositories for the disposal of spent nuclear fuel and high-level radioactive wastes. Starting with a comprehensive list of radionuclides present in the waste form, a multi-step down-selection process evaluates each isotope’s potential relative contribution to the total peak exposure dose, which is a surrogate metric for overall repository safety. In the first screening step, only basic, readily available characteristics of a radionuclide are needed, such as its inventory, half-life, specific activity, and dose coefficient. In the second step, the radionuclide’s transport time from the repository to the accessible environment is estimated based on factors affecting its mobility and retardation. By adjusting the screening threshold, the number of radionuclides considered potentially safety-relevant can be changed, thus yielding a larger or smaller (more or less conservative) set of radioisotopes being tracked in the performance assessment model, as warranted by the stage of repository development. We exercise the proposed screening approach for a particular waste form—spent nuclear fuel assemblies—and two disposal pathways—deep horizontal and vertical borehole repositories. An integrated performance assessment model is then used to simulate the migration of a considerably larger set of radionuclides from the disposal canisters to the land surface. The acceptably small difference in peak dose calculated with the comprehensive and reduced set of radionuclides indicates the appropriateness of the proposed screening approach.

Dawei SU, Yihui FAN, Tianhui ZHAO et al.

With large scale integration of renewable energy, motivating valley-filling users to participate in power grid regulation to tap the valley-filling potential of charging loads has become one of the important means to enhance the space for renewable energy consumption. Firstly, an evaluation framework for valley-filling potential of urban public charging stations is built in this paper. Probability modeling is conducted on charging orders, and a random sampling-based Monte Carlo simulation is carried out to obtain the sampling data representing the starting charging time. Then, the typical load characteristic indicators including valley-period and flat-period load rates are proposed, and the charging load valley-filling potential evaluation parameters are introduced to carry out valley-filling potential evaluation of urban public charging stations. Finally, based on the actual charging order data of the urban charging stations in a pilot city under different price incentives, a quantitative evaluation of the valley-filling potential of urban public charging stations is carried out. The results show that the simulated charging load is consistent with the actual load in tendency, and the change pattern is similar to the actual situation. When the service fee discount exceeds 30%, for every additional 10% discount, the average valley-filling response will increase by approximately 23.6 MW. Therefore, the proposed evaluation framework realizes the quantification of valley filling potential of public charging stations.

Teruya Nakagawara, Minoru Kanega, Shunsuke C. Furuya et al.

Electric-field controls of Dzyaloshinskii-Moriya interactions (DMIs) have recently been discussed from the microscopic viewpoint. Since the DMI plays a critical role in generating topological spin textures (TSTs) such as the chiral soliton, the magnetic skyrmion, and the magnetic hedgehog, electric-field controls of these TSTs have become an important issue. This paper shows that such electric-field-induced DMI indeed creates and annihilates TSTs by numerically solving the Landau-Lifshitz-Gilbert (LLG) equation for many-body spin systems at finite temperatures. We show that when a strong electric field is applied in a proper way to one- or two-dimensional ferromagnets, the Hamiltonians are changed into the well-known spin models for the chiral soliton or the skyrmion lattice, and the TST states emerge. We utilize a machine-learning method to count the number of generated TSTs. In the three-dimensional (3D) case, we demonstrate the electric-field induction of a magnetic hedgehog structure as follows: Applying a strong enough electric field along a proper direction to a skyrmion-string state (a triple-$\boldsymbol{q}$ state) at low but finite temperatures, we find that the field-induced DMI can drive a quadruple-$\boldsymbol{q}$ state with hedgehog-antihedgehog pairs. This result indicates that we have succeeded in constructing a simple 3D short-range interacting spin model hosting a magnetic hedgehog structure.

Suwei ZHAI, Yinyin LI, Fan DU et al.

In view of the influence of unconventional safety risks on new power systems, a two-layer cooperative reactive power control strategy considering the uncertainty of source load was proposed. The reactive power optimization model of distribution network was established with the aim of minimizing the loss of distribution network and considering various regulation equipment constraints. The distribution network distributed reactive power optimization solution framework was constructed. The outer layer adopted the adaptive overrelaxation penalty parameter alternating direction method of multipliers (ADMM) for global update iterative solution. In the inner layer, the column-and-constraint generation (C&CG) algorithm was used to solve the two-stage distributionally robust reactive power optimization model for each region. The proposed strategy can effectively improve the solving efficiency of distributed reactive power optimization model, reduce network losses, and improve the stability of the new power system.

Jun Xie, Zhe Zhou, Ziqian Liu et al.

Abstract Fibre‐reinforced polymer (FRP)/rigid polyurethane foam (RPUF) interface is susceptible to moisture intrusion in addition to natural ageing during operation. This study investigated the influence of moisture intrusion on the FRP/RPUF interface under natural ageing using experiments and molecular dynamics (MD) simulations. Water absorption, shear strength, and leakage current tests were used to clarify the changes in the interface performance. The degradation mechanism of moisture intrusion at the interface under natural ageing was revealed by MD simulation and micro‐characterisation. The results show that the natural ageing of interfacial materials will slightly reduce the quality of the interface but will reduce the water resistance of the material and promote the process of water intrusion into the interface. In addition, water mainly invades the interface through RPUF. After water penetration, the interfacial bonding strength and insulation performance significantly decreased. Plasticisation and hydrolysis of interfacial materials are the main reasons for decreased interfacial adhesion. Hydrolysis can cause irreversible damage to the interface, increasing interface defects and water absorption. The vicious cycle of material hydrolysis is the ultimate cause of interfacial debonding. The polar molecules produced by this process and the water absorbed by the interface caused the degradation of the interface insulation performance.

Qi Qi, Yunuo Fan, Xinyuan Cao et al.

Abstract The wide‐angle electromagnetic scattering problems can be rapidly solved by using the method of moments in conjunction with compressive sensing theory. The method mainly has two computational parts: measurement and recovery. To further enhance the performance, an improved orthogonal matching pursuit algorithm with a randomised atom selection process is proposed, significantly reducing the computational complexity of the recovery part. Additionally, a restart mechanism is designed to eliminate possible errors that might occur during the random process, ensuring the accuracy of recovery results. Numerical experiments with objects of different shapes validate the effectiveness and efficiency of the proposed scheme.

N. Khan, M. Bilal, R. Ali et al.

In this manuscript, a 16-port compact multi-antenna array for fifth generation (5G) communications is presented. The proposed antenna offers high data rate communication, by using MIMO (multiple-input-multiple-output) wireless technology. Efficient bandwidth enhancement techniques are used to achieve wider bandwidth response i.e., 3.4-3.8 GHz within sub-6GHz. This system is realized over low-cost FR-4 laminate having dimensions of 64mm × 131mm. The fractal shape slotted radiators and open-ended square ring (OESR) isolating structures achieves at least 25dB isolations among antenna pairs while maintaining wideband response. The optimum isolation, low-cost design profile, matched scattering parameters without compromising compactness and acceptable specific absorption rate (SAR) makes this system a suitable candidate for 5G smart phone communications.

Gang Zhang, Minghan Shu, Kam Weng Tam et al.

Abstract In this study, a direct synthesis approach is proposed to extract the coupling matrix of multi‐port filtering power divider (FPD) with arbitrary phase shift, power division as well as reference impedances, for the first time. This method provides an attractive technique to synthesise a multi‐functional device that combines the characteristics of bandpass filter, multi‐port power divider and ideal phase shifters as well as the impedance matching network, which can effectively diminish the overall size and improve the performance of the microwave front‐end network. A newly defined coupling matrix corresponding to arbitrary multi‐port topologies that introduces ideal phase shift by virtue of constant frequency‐independent reactance at the source and load is developed in FPD synthesis process. The coupling matrix is obtained directly by optimising the presented cost‐function in this paper, avoiding complex similar transformation process of coupling matrix. Finally, several numerical examples of multi‐port FPD with equal/unequal power division ratio, arbitrary phase shift and reference impedances are synthesised to well verify the proposed synthesis method, and a practical example is given to verify the validity of arbitrary phase shift and arbitrary reference impedance.

S. Kuschert, M. Stroet, Y. K.-Y. Chin et al.

<p>Peptides and proteins containing non-canonical amino acids (ncAAs) are a large and important class of biopolymers. They include non-ribosomally synthesised peptides, post-translationally modified proteins, expressed or synthesised proteins containing unnatural amino acids, and peptides and proteins that are chemically modified. Here, we describe a general procedure for generating atomic descriptions required to incorporate ncAAs within popular NMR structure determination software such as CYANA, CNS, Xplor-NIH and ARIA. This procedure is made publicly available via the existing Automated Topology Builder (ATB) server (<span class="uri">https://atb.uq.edu.au</span>, last access: 17 February 2023) with all submitted ncAAs stored in a dedicated database. The described procedure also includes a general method for linking of side chains of amino acids from CYANA templates. To ensure compatibility with other systems, atom names comply with IUPAC guidelines. In addition to describing the workflow, 3D models of complex natural products generated by CYANA are presented, including vancomycin. In order to demonstrate the manner in which the templates for ncAAs generated by the ATB can be used in practice, we use a combination of CYANA and CNS to solve the structure of a synthetic peptide designed to disrupt Alzheimer-related protein–protein interactions. Automating the generation of structural templates for ncAAs will extend the utility of NMR spectroscopy to studies of more complex biomolecules, with applications in the rapidly growing fields of synthetic biology and chemical biology. The procedures we outline can also be used to standardise the creation of structural templates for any amino acid and thus have the potential to impact structural biology more generally.</p>

Xinyu Bu, Changhong Yang, Mengjia Fan et al.

Lead-free ([Formula: see text][Formula: see text])NbO3 (KNN) and [Formula: see text]([Formula: see text][Formula: see text])[Formula: see text]NbO3 (LKNN) thin films were fabricated by a sol-gel method. The effects of Li substitution on crystal structure, microstructure and electrical properties of KNN film were systematically studied. Li doping can enhance the ferroelectric and piezoelectric properties of KNN film. Compared with pure KNN film, the LKNN film possesses larger remanent polarization ([Formula: see text] [Formula: see text] 9.3 [Formula: see text]C/[Formula: see text]) and saturated polarization ([Formula: see text] [Formula: see text] 41.2 [Formula: see text]C/[Formula: see text]) and lower leakage current density ([Formula: see text]A/[Formula: see text] at 200 kV/cm). Meanwhile, a typical butterfly shaped piezoelectric response curve is obtained in the LKNN film with a high piezoelectric coefficient ([Formula: see text] [Formula: see text] 105 pm/V). Excellent fatigue resistance ([Formula: see text][Formula: see text] switching cycles) and aging resistance ([Formula: see text] 180 days) demonstrate the long-term working stability of LKNN film. These findings indicate that KNN-based lead-free piezoelectric films have a broad application prospect in microelectromechanical systems (MEMS).

Meng Xiao, Mengdie Zhang, Boxue Du

Abstract The degradation of dielectric properties of polypropylene (PP) at high temperature affects the operational stability of metallised film capacitors. This study presents a method to improve the high‐temperature dielectric performance of PP through long‐chain branching modification and regulating the crystalline properties. Different amounts of nucleating agents were added to long‐chain branched polypropylene (LCBPP) to study the effect of crystallisation on electrical properties. The results show that the long‐chain branches improve thermal stability by enhancing the chain entanglement, and also increase the number of crystals due to heterogeneous nucleation. The addition of nucleating agents promotes the crystallisation of LCBPP, which increases the nucleation density and improves the crystallinity. The regulation of the microstructure of PP suppresses the relaxation of the chains and limits the charge transport. The dielectric constant of the modified films with long‐chain branching is slightly increased, and the doping of nucleating agents has little effect on the dielectric constant and loss of LCBPP. At 125°C, the conductivity of the modified LCBPP films with the addition of 0.05 wt% nucleating agent decreased by 2 orders of magnitude and the breakdown strength increased by 26.3%. This study has implications for improving the dielectric properties of PP films.

Deliang XIANG, Yihao XU, Jianda CHENG et al.

Synthetic Aperture Radar (SAR) image registration has recently been one of the most challenging tasks because of speckle noise, geometric distortion and nonlinear radiation differences between SAR images. The repeatability of keypoints and the effectiveness of feature descriptors directly affect the registration accuracy of feature-based methods. In this paper, we propose a novel Feature Intersection-based (FI) keypoint detector, which contains three parallel detectors, i.e., a Phase Congruency (PC) detector, horizontal/vertical oriented gradient detectors, and a Local Coefficient of Variation (LCoV) detector. The proposed FI detector can effectively extract keypoints with high repeatabilityand greatly reduce the number of false keypoints, thus greatly reducing the computational cost of feature description and matching. We further propose the Siamese Cross Stage Partial Network (Sim-CSPNet) to rapidly extract feature descriptors containing deep and shallow features, which can obtain more correct matching point pairs than traditional synthetic shallow descriptors. Through the registration experiments on multiple sets of SAR images, the proposed method is verified to have better registration results than the three existing methods.

Lili WANG, Hao WANG, Zhouyang REN et al.

The rapid growth of grid-connected installed capacity of wind power and photovoltaic power has brought great challenges to the safe operation of the power system. Exploiting the flexible resources of the power grid is an effective way to ensure the healthy development of renewable energy. Therefore, this paper proposes an evaluation method for accommodation capacity of high voltage distribution networks considering the regulation potential of flexible resources. Firstly, a set of typical scenarios of wind power, photovoltaic and load are produced based on the fuzzy C-means clustering algorithm. Then, taking into account the flexibility of hydropower and power grid, a renewable energy planning model is established with the maximum renewable energy accommodation capacity of distribution networks as objective and with a comprehensive consideration of the normal operation states and the N–1 contingency states of distribution networks. Finally, the effectiveness of the proposed model and method are verified through case study of an 110 kV high voltage distribution network.

Li Cai, Qiang Hu, Jianguo Wang et al.

Abstract In 2018–2019, two types of rocket‐triggered lightning tests, that is, striking to ground and distribution line, were conducted in Guangdong, China. The main focus of this paper is to compare the waveform parameters of the return strokes (RS) from the two tests. For current, the 10%–90% risetime of RS from lightning striking to distribution line is 2.4 times higher than that striking to ground, and the differences in the other parameters are small. For close magnetic field, the RS from lightning striking to distribution line have a lower peak (30% lower after considering the peak current) and a larger risetime and half‐peak width time; besides, it is necessary to divide the front edge of the close magnetic field waveform into two parts: leader (BL) and return stroke (BRS). For close electric field, the close RS electric field peak (ERS) was less sensitive to distance than the leader electric field peak (EL). For far electric field, the differences in waveform parameters of RS from the two tests were not significant, but after considering the peak current, the normalised initial electric field peak (EP) of RS from lightning striking to distribution line was 14% lower than that striking to ground.

Sheng Zhang, Yadong Fan, Qingquan Lei et al.

Abstract The high‐voltage isolated energy supply transformer (HIET) is the key component of the HVDC breaker, which is used for energy transmission and the potential isolation. There is a lack of research results that can meet engineering applications at home and abroad. The design of a 500 kV HIET with dry‐type insulation is proposed, using 10 cascade connected 50 kV sub‐transformers (STs), which uses silicon rubber suitable for DC voltage as the main insulation material. High‐voltage (HV) winding of ST adopts double‐shielding structure of coil semi‐conductive shielding and inner semi‐conductive shielding to improve electric field distribution. The simulation analysis of an electric field at different insulation thicknesses and temperatures shows that the electric field decreases with an increase in thickness of insulation. When the thickness is greater than 25 mm, the electric field reduction effect is significantly weakened. The electric field is closely related to temperature, when at 20°C, the electric field between double‐shielding is relatively uniform. When at 70°C, the inner shielding electric field is much higher than coil shielding, and undergoes obvious reversal. In addition, the 500 kV HIET's electric field has been analysed. The 50 0kV HIET prototype has been manufactured and passed the type test, and successfully applied to the 500 kV Zhangbei DC grid project.

Mohammad Omid Bagheri, Hamid Reza Hassani, Abdel Razik Sebak

Abstract The design strategy to stabilise the phase centre (PC) of the conventional horn antenna using a shaped dielectric rod is presented for aperture efficiency improvement of space‐fed antennas. In most practical horn antennas, PC location has significant variations with frequency leading to phase error loss and aperture efficiency reduction over the bandwidth of interest. To overcome this drawback, based on physical reasoning, shaped dielectric rods with appropriate excitation mode are designed and placed on the aperture of conventional rectangular and conical horn antennas. The simulation results show that using a shaped dielectric rod inside the horn antenna leads to a decrease in phase‐centre variations versus frequency without disturbing the radiation pattern and reflection coefficient. To investigate the performance, a conical corrugated horn antenna loaded by a conical tapered dielectric rod is used as a feed of the transmitarray antenna. Using a shaped dielectric rod fabricated by 3D printing technology, the PC variations of the proposed horn decrease from 1.06 λ to 0.08 λ over the X‐band (λ at 8 GHz). The measurement of the fabricated transmitarray antenna shows an improvement of maximum aperture efficiency from 55% to 64.7% at 10 GHz. The aperture efficiency bandwidth above 50% level is also increased from 1 to 2.2 GHz.

Li GUAN, Lei ZHOU, Hanghang LIU et al.

With the rapid growth of wind power and photovoltaic new energy generation capacity, accelerating the improvement of energy storage facilities participating in the electricity spot market trading mechanism is conducive to consumption of new energy. In order to improve the regulation ability of the power system, taking the trading mechanism of Shandong independent electric energy storage participating in the spot market as the research object,the operation mechanism of independent electric energy storage participating in the spot market in the self scheduling mode is proposed. The simulation operation data shows that the participation of energy storage devices in the spot market plays an important role in promoting the consumption of new energy and improving the power supply guarantee capacity.

David Romero Abad

We calculate the magnetic field generated by a steady current that takes the shape of two types of special curves: hypocycloids and epicycloids with n numbers of sides. The computation was performed in the center of the referred curves. For this purpose, we use the Biot-Savart law which is studied in every introductory-level electricity and magnetism course. The result is quite general because it is obtained as a function of the number of sides of the curve and in terms of a parameter ϵ that identifies the type of curve considered (ϵ = −1 hypocycloids and ϵ = + 1 epicycloids).

Zhangmeng LIU, Shuo YUAN, Shiqian KANG

Retrieving the working modes of multifunction radar from electronic reconnaissance data is a difficult problem, and it has attracted widespread attention in the field of electronic reconnaissance. It is also an important task when extracting benefits from big electromagnetic data and provides straightforward support to applications, such as radar type recognition, working state recognition, radar intention inferring, and precise electronic jamming. Based on the assumption of model simplicity, this study defines a complexity measurement rule for multifunction radar pulse trains and introduces the semantic coding theory to analyze the temporal structure of multifunction radar pulse trains. The model complexity minimization criterion guides the semantic coding procedure to extract radar pulse groups corresponding to different radar functions from pulse trains. Furthermore, based on the coded sequence of the pulse train, the switching matrix between different pulse groups is estimated, and the hierarchical working model of multifunction radars is ultimately reconstructed. Simulations are conducted to verify the feasibility and performance of the new method. Simulation results indicate that the coding theory is successfully used in the proposed method to automatically extract pulse groups and rebuild operating models based on multifunction radar pulse trains. Moreover, the method is robust to data noises, such as missing pulses.