Hasil untuk "Electricity and magnetism"

Zhongyu LI, Haozhuo PI, Jun’ao LI et al.

Bistatic Synthetic Aperture Radar (BiSAR) needs to suppress ground background clutter when detecting and imaging ground moving targets. However, due to the spatial configuration of BiSAR, the clutter poses a serious space-time nonstationary problem, which deteriorates the clutter suppression performance. Although Space-Time Adaptive Processing based on Sparse Recovery (SR-STAP) can reduce the nonstationary problem by reducing the number of samples, the off-grid dictionary problem will occur during processing, resulting in a decrease in the space-time spectrum estimation effect. Although most of the typical SR-STAP methods have clear mathematical relations and interpretability, they also have some problems, such as improper parameter setting and complicated operation in complex and changeable scenes. To solve the aforementioned problems, a complex neural network based on the Alternating Direction Method of Multiplier (ADMM), is proposed for BiSAR space-time adaptive clutter suppression. First, a sparse recovery model of the continuous clutter space-time domain of BiSAR is constructed based on the Atomic Norm Minimization (ANM) to overcome the off-grid problem associated with the traditional discrete dictionary model. Second, ADMM is used to rapidly and iteratively solve the BiSAR clutter spectral sparse recovery model. Third according to the iterative and data flow diagrams, the artificial hyperparameter iterative process is transformed into ANM-ADMM-Net. Then, the normalized root-mean-square-error network loss function is set up and the network model is trained with the obtained data set. Finally, the trained ANM-ADMM-Net architecture is used to quickly process BiSAR echo data, and the space-time spectrum of BiSAR clutter is accurately estimated and efficiently restrained. The effectiveness of this approach is validated through simulations and airborne BiSAR clutter suppression experiments.

Mariam, Mariam, Manish Joshi et al.

IntroductionA significant quantity of radioactive iodine is expected to be released following severe nuclear reactor accidents. Recent studies have shown that among various species expected, iodine oxides (IxOy) are less explored but play a crucial role in nuclear safety assessments due to their impact on source term evaluation. Therefore, this study was designed to generate and characterize iodine oxides in a laboratory scale setup.MethodsExperiments were conducted at room temperature and ambient relative humidity using an I2 concentration of ∼1 ppm and an O3 concentration of ∼30 ppm inside a controlled chamber. The reaction kinetics were determined by continuously monitoring O3 concentration. While many previous studies have relied on the radioactive iodine tracers and gamma spectroscopy, this study adopts an alternative approach by analysing ozone decay as a proxy for iodine oxidation. The generated iodine oxide aerosols were characterized for their physical and chemical properties. Impactors and gross samplers were used to collect aerosols, giving particle mass size distribution and total mass concentration, respectively. Particle morphology and chemical composition were determined using a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS).Results and discussionThe reaction kinetics showed that ozone decay followed first-order kinetics with a high correlation (R2 > 0.99). The particles were found to have I2O5 chemical species with varied shapes, from small porous cloud-like structures to large rod-shaped particles. The findings provide valuable insights into iodine oxidation under environmentally relevant conditions, bridging knowledge gaps in source term estimation and contributing to the enhancement of accuracy of the modeling codes for nuclear safety applications.

Teruo Matsushita

Shuang Qiu, Jianlin Ye, Renli Zhang et al.

Abstract In a phased array radar, the phase quantisation error of phase shifters can lead to the beam steering error (BSE) between the predetermined and the actual directions. Existing researches on phase feeding optimisation suffer from high computational complexity and large storage space. In this study, an equivalent monopulse method is first proposed to yield the BSE with O(N) complexity by formulating the equation between the phase quantisation error and BSE. Further, a symmetric phase feeding compensation (SPFC) method is developed on the basis of the proposed scheme to cancel the phase quantisation error employing a symmetric planar array. Subsequently, a random phase compensation method is formulated to further reduce the residual quantisation errors of SPFC, and a random symmetric phase feeding compensation (RSPFC) method is proposed. The proposed SPFC and RSPFC methods possess O(N) complexities and allow for parallel calculation of element phase feedings, thus making the proposed methods more applicable on the embedded beam controller of a phased array radar. Based on computer simulations and phased array radar experiments, the proposed SPFC and RSPFC methods are validated to yield superior beam pointing accuracies and can improve the fluctuations in angle tracking.

Tiecheng LI, Hui FAN, Qian ZANG et al.

The linear section location method based on remote signaling data does not consider the influence of communication time-delay and reliability, and is only applicable to large current faults and single faults. In this regard, a multi-point synchronous protection scheme for active distribution network based on 5G communication is proposed. Firstly, a section location communication architecture based on 5G communication is established, and its communication time-delay and reliability are analyzed. Secondly, on the basis of analyzing the direction distribution characteristics of the transient zero-sequence current, the switching function is redefined, and a logical relationship location model suitable for small current faults is proposed. Then, using the left-right approximation method, the switching function established according to the logic relationship is linearized, which makes the linearized logic relationship location model not only suitable for single faults, but also for multiple faults. Finally, the proposed protection scheme is validated in an active distribution network with different topologies and 5G communication. The results show that the proposed scheme can not only realize multi-point synchronous protection, but also be applicable to both small current faults and multiple faults.

Shuqi Li, Qiang Wang, Dongxin He et al.

Abstract The oil‐pressboard insulation on the valve side of the converter transformer withstands pulsating square wave voltage. The voltage contains lots of DC components and high‐order harmonics, which is likely to cause insulation failures. The partial discharge and space charge experiments of oil‐impregnated pressboard under DC superimposed harmonic voltage are conducted to study the effects of harmonic frequency and DC components on the discharge and charge accumulation and to explore the correlation mechanism of charge dynamic behaviour and discharge. Firstly, it is found that high‐order harmonic voltage promotes the partial discharge generation, but DC component suppresses the discharge. Moreover, the charge inside the pressboard is mainly injected in the same polarity and accumulates over time. The space charge density near the electrode increases with the increase of harmonic frequency, and the large amount of charge injection leads to electric field distortion. Meanwhile, the electric field direction changes faster, and the frequent charge injection and extraction behaviours make the charge recombination intensify, which promotes the discharge. Through the above analysis, the influence law of harmonic voltage on the failure of oil‐pressboard insulation is obtained, providing a theoretical basis for the structural optimisation and condition assessment of the converter transformer insulation.

حامد معظمی گودرزی, علیرضا دولت آبادی

سامانه‏ های پروازی متعددی با کاربردهای گسترده در زمینه‏ های مختلف علمی، صنعتی، و تجاری وجود دارند. یکی از بخش‏های مورد استفاده در این ساختارها، رادار است. بسیاری از کاربردهای این سامانه‏ ها، نیازمند ردگیری اهداف یا جهات در محدوده زاویه ‏ای باریک است. این ویژگی با به ‏کارگیری آنتن‏هایی دارای پهنای پرتو باریک به‏ دست می ‏آید. آنتن‏های آرایه ‏ای، می‏ توانند در کنار فراهم نمودن بهره مورد نیاز، تحقق بخش چنین نیازی باشند. همچنین، این پهنای پرتو باید در محدوده قابل قبولی از جهات مختلف قابل تنظیم باشد. چنین ویژگی تنظیم پذیری به کمک استفاده از آنتن‏های آرایه فازی تحقق پذیر است. قابلیت تغییر جهت گلبرگ اصلی یک چنین آنتنی، به کمک ادوات فعال تغییر دهنده فاز تغذیه آنتن‏های موجود در آرایه، مانند دیودهای پین و ادوات فریت، فراهم است. با این حال، استفاده از ادوات غیرفعال ماتریس باتلر ابزاری ساده ‏تر و ارزان‏تر برای تحقق چنین راهکاری به‏ شمار می‏ آید. به‏ کارگیری ماتریس باتلر با تعداد درگاه ورودی-خروجی بیشتر منجر به الگوی تشعشعی با پهنای باند باریک‏تر می ‏شود. در این مقاله، طرحی ساده از ماتریس باتلر 32×32 در طیف فرکانسی باند X معرفی، و نتایج شبیه ‏سازی عملکرد آن ارائه می‏شود. این شبیه‏ سازی ‏ها به‏ کمک نرم ‏افزار کامسول که مبتنی بر روش اجزای محدود است اجرا شده ‏اند. در نهایت، پس از اِعمال موج به دو درگاه ورودیِ مشخص و اتصال ساختار ماتریس باتلر به آرایه مایکرواستریپ، پهنای پرتوی 3/5 درجه به‏ دست می ‏آید. دست‏یابی به تشعشع با پهنای پرتو باریک بر اساس آرایه آنتن‏های مایکرواستریپ تغذیه شده با ماتریس باتلر 32×32 و تنها بر پایه بُرد تک ‏لایه، هدف اصلی این پژوهش است.

GUO Jiangfeng, MACMILLAN Bryce, BALCOM Bruce

Nuclear magnetic resonance (NMR) is a non-destructive technique that can reveal the phase structure and dynamics of polymers at the molecular level. It is sensitive to polymer chain mobility and requires minimal special sample preparation. We investigated the phase structure and molecular dynamics of polyurethane rubber (PUR) based on the T1-T2* relaxation correlation spectra, and analyzed the T1-T2* data by multi modal decay. The T1-T2* spectra showed three types of signals: rigid 1H with the shortest T2* value, interphase 1H with an intermediate T2* value, and mobile-amorphous 1H with the longest T2* value. The three 1H components exhibit the similar T1 values in PUR, which decreased with increasing hardness or decreasing temperature. The integrals of these signals depend on the durometer hardness and temperature for PUR. They increase for the rigid phase but reduce for mobile-amorphous phase and interphase with an increase of PUR durometer hardness. The rigid 1H component decreased and the mobile-amorphous 1H component increased with increasing temperature, while the interphase 1H component remained constant. In addition, the hard/soft ratio decreased with increasing temperature for PUR systems. These results indicated that T1-T2* spectra can be used to characterize phase structure and dynamics of PUR.

Zhen WANG, Dong LIU, Chongyou XU et al.

In the context of energy transition, the new power system is being built continuously with the goal of being clean and low-carbon, open and interactive. With the fast development of monitoring technology and communication technology, the data sources of power system have become more diverse and the structures of the data have become more complex, which provides a data basis for and at same time brings new challenges to the new power system data fusion. Firstly, the data characteristics of the new power system are analyzed and the data fusion requirements of the new power system are proposed. Then the data model of the new power system and the hierarchical division of multi-source heterogeneous data fusion technologies are introduced, and the advantages and limitations of the key fusion technologies and their applicable scenarios are analyzed. The data requirements, data sources, fusion objectives, common methods and research difficulties of multi-source heterogeneous data fusion technologies are summarized under five typical scenarios, including transmission and distribution collaboration, source-grid-load-storage collaboration, virtual power plants, multi-type loads, and electricity-carbon trading. Finally, the future prospects of the new power system data fusion technology are explored.

Yantao LOU, Xiaoping SUN, Qi LIU et al.

The reverse recovery characteristics of the diode plays an important role in IGCT-MMC. This paper firstly introduces the reverse recovery characteristics of the fast recovery diode. Then the switching behaviors of the fast recovery diode in the IGCT-MMC topology are analyzed. Finally a double-pulse experimental platform is built for IGCT-MMC testing, and the reverse recovery characteristics of three commercial fast recovery diode products are compared. The test results show that the reverse recovery peak current and power of the fast recovery diode have a linear relationship with di/dt, and the testing result at high temperature are higher than that at room temperature. While under the same di/dt and temperature conditions, different fast recovery diodes have different reverse recovery peak currents and powers in IGCT-MMC. As a result, it is necessary to choose a suitable di/dt according to the safe working area of the diode in IGCT-MMC.

Xuesong ZHOU, Chenglong WANG, Youjie MA et al.

In the process of asynchronous motor vector control, the motor speed information is obtained through the speed measuring devices. Influenced by such factors as interference, quantization errors, and motor operating conditions, the detection elements gives the speed information mixed with noise that needs to be filtered, but the traditional speed filtering method cannot consider both real-time and precision requirements. The linear extended state observer (LESO) has the function of filtering the output signal of the system. The traditional LESO channel is added with filtering to improve the noise suppression ability, and the observer is upgraded to improve the observation ability, thereby improving the contradiction between the system response speed and controller noise suppression. In the frequency domain, the improved linear active disturbance rejection controller is analyzed through the Bode diagram in terms of stability, tracking and anti-disturbance. The theoretical analysis shows that the improved active disturbance rejection controller can reduce the effects of the noise at the controller input and system feedback. The simulation results have verified the effectiveness of the controller in noise suppression.

Marina Jordão, Daniel Belo, Rafael F. S. Caldeirinha et al.

Abstract The main objective of this study is to present a characterization system that can be used to measure the active reflection coefficient of each port of the multiple input multiple output (MIMO) antennas, when the main beam is steered to an intended direction. Since MIMO systems are composed of antennas with several elements and each antenna element is connected to a power amplifier, an active component, the beamforming will contribute to the mismatch of each branch. To this extent, a calibrated measurement system has been implemented using off‐the‐shelf software defined radio and designed to effectively extract such coefficients, when all the ports are simultaneously excited. Results for linear and planar MIMO antenna arrays have been experimentally obtained for several beam directions and the impact of beamforming on each element of the antenna is presented and compared to simulated results. Additionally, their behaviour was also assessed when some of the radiation elements are deliberately disconnected, mimicking those not working properly.

Xiaofei XIA, Yufeng LU, Yi SU et al.

The vibration signals generated by transmission and impact of circuit breaker mechanical components have chaotic characteristics, which are difficult to be analyzed with conventional signal processing methods. Firstly, the vibration signals are reconstructed into a high-dimensional space by mutual information method and Cao algorithm, and the permutation entropy is calculated as the feature vector. And then the support vector machine (SVM) is used to identify the mechanical fault types of circuit breakers. Finally, the PSO improved GSA hybrid algorithm is used to optimize the parameters of SVM, and the measured vibration signals of the circuit breakers are used to verify the results. The results show that the characteristics of circuit breaker vibration signals can be accurately extracted with combination of phase space reconstruction and permutation entropy. The PSO-GSA-SVM can quickly and effectively identify the fault types of circuit breakers, thus providing an effective solution to such problems as path distortion, energy leakage and mode overlap of existing diagnosis methods.

Chandana SaiRam, Damera Vakula, Mada Chakravarthy

In this paper, a novel compact broadband antenna at UHF frequencies is presented with canonical shapes. Hemispherical, conical and cylindrical shapes have all been considered for antenna configuration. The designed antenna provides an instantaneous frequency range from 370 to 5,000 MHz with omnidirectional characteristics. The antenna was simulated in CST Microwave Studio, fabricated and evaluated; the results are presented. The simulated and measurement results are in good agreement. The antenna has voltage standing wave ratio (VSWR) ≤ 1.9:1 in 400–570 MHz, 2,530–3,740 MHz and 4,180–4,620 MHz; it has VSWR ≤ 3:1 over the operating frequency range 370–5,000 MHz and the measured gain varies from −0.6 to 4.5 dBi over the frequency band. The concept of canonical-shaped antenna elements and the incorporation of triple sleeves resulted in a reduction of the length of the antenna by 62% compared to the length of a half-wave dipole antenna designed at the lowest frequency. The antenna can be used for trans-receiving applications in wireless communication.

Yogesh Kumar, Jaswinder Pal, Parambir Singh Malhi et al.

The perovskite (La0.7Ba0.3)(Mn0.5Fe0.5)1−xZrxO3, where x = 0.1, 0.2 and 0.3, ceramics were synthesized by solid-state reaction method. The introductory structural studies were followed through by X-ray diffraction technique and the results have disclosed that all the samples were crystallized into an isolated phase. The Zr substitution in the resulting solid solutions increases the electrical conductivity and the maximum value of ac conductivity has been found to be ∼118.8 S . cm−1 for x = 0.3 at 200∘C (at 1 MHz). The frequency dependence of ac conductivity data follows Jonscher’s power law. The variation of the exponent n versus temperature follows the nonoverlapping small polaron tunneling (NSPT) model. The dielectric relaxation has been observed to be of non-Debye nature for all measuring temperatures (50–200∘C). The impedance spectroscopy reveals that all the samples exhibit negative temperature coefficient of resistance (NTCR) behavior. The prepared samples (for x > 1) are supposed to be suitable for cathode materials in SOFCs.

Fengqi Wang, Wei Cai, Chunlin Fu et al.

The electronic structure and optical properties of Ca3(Mn1−xTix)2O7 (x=0, 1/8, 2/8, 3/8, 4/8) were studied by first-principle calculations within the generalized gradient approximation approaches (GGA). The lattice constants of Ca3(Mn1−xTix)2O7 increase with the increase of Ti4+ content caused by the substitution of Ti4+ with larger ionic radius for Mn4+. Ca3(Mn1−xTix)2O7 is a direct band gap semiconductor, and the band gap (Eg) increases with the increase of Ti4+ content. From the density of states, the introduction of Ti-3d states can weaken the effects of Mn-3d states on the bottom of conduction band and has little influence on O-2p states on the top of valence band. The introduction of nonmagnetic Ti4+ ions can weaken the magnetism of Ca3(Mn1−xTix)2O7. According to the Mulliken population analysis, it is found that the introduction of Ti4+ enhances the electronic accepting capacity of oxygen ions and enhances the electronic losing capacity of manganese ions. The bond strength of Ti–O covalent bond is stronger than that of Mn–O covalent bond. Furthermore, the optical properties of Ca3(Mn1−xTix)2O7 was calculated. As Ti4+ content increases, the absorption edge of Ca3(Mn1−xTix)2O7 has a blue shift, the static refractive index n0 decreases, the static dielectric constant ε1(0) decreases, the position of loss peak moves to higher energy.

YANG Yun-han, DU Yao, YING Fei-xiang et al.

An inclusion complex of naringenin (NAR) and β-cyclodextrin (βCD) was prepared with ultrasonication. Powder X-ray diffraction (XRD) and infrared absorption spectroscopy (IR) indicated that the inclusion complex formed had some new physical/chemical properties. 1H NMR and ROESY spectroscopy revealed that the stable supramolecular inclusion complex was formed by having the benzene ring of NAR introduced into the big end of the βCD. The formation processes of NAR/βCD inclusion complex were also studied by quantum chemical calculations. It was revealed that enthalpy and hydrogen bonding weak interaction force were the driving forces behind the formation. The optimal inclusion mode obtained from energy gap and binding energy analyses were consistent with the most inclusive mode obtained from molecular docking analysis and the NMR results. These results were further confirmed by ONIOM calculation.

Yu HAN, Chao FAN, Guangke WANG et al.

By collecting the sound pressure signals of the aerodynamic noise of the converter transformer fans, the electric field noise of the smoothing reactors and the electric field noise of the DC/ AC filter field in the 800 kV converter station, the spectrum characteristics of the sound pressure signals of different locations are analyzed under the load condition, and the low-frequency and A-weighted sound level noise values of each noise signal are given. It is concluded that the noise of HVDC convert stations covers the low-, mid- and high-frequency bands, and various types of noise signals have similar spectrum characteristics; the low-frequency energy makes up larger portion of the total noise energy, and the low-frequency noise value of the fans is much higher than that of other converter station outdoor equipment under the same test condition.

John Henao, Lorenzo Martinez-Gomez

Abstract Rare-earth perovskites-type oxides are compounds with the general formula ABO3. There are many industrial and research applications related to their properties such as photocatalytic activity, magnetism, or pyro-ferro and piezo-electricity, and interest in these compounds in the field of energy storage and conversion is growing. Rare-earth perovskite-type oxides may be used in nickel–metal hydride (Ni/MH) battery technology because these materials may store hydrogen in strong alkaline environments, and also because of their abundance and low cost. In this review, the use of rare-earth perovskite-type oxides in Ni/MH batteries is described, starting from their crystalline structure and production methods. In each category, a description concerning the latest advances and future research direction is presented. Electrochemical performance of the perovskite-type electrodes is reviewed extensively. In addition, various strategies for enhancing their hydrogen storage capacity as a negative electrode in hydrogen batteries are discussed. Drawbacks and challenges of this technology are also presented. Graphical Abstract

Li Jiao Gong, Cheng Liang Pan, Qiao Sheng Pan et al.

Ferroelectric single crystals, such as PZN-PT, provide novel prospects in piezoelectric bending devices such as actuators, sensors or energy harvesters because of their extraordinarily large piezoelectric coefficients. However, large errors may occur in some analyses on electromechanical behaviors using the conventional models. We find the bending rigidity of piezoelectric composited bender is affected not only by thickness, width and the modulus of elasticity of the different layers but also electromechanical coupling coefficients (EMCCs) of the piezoelectric material and the larger EMCCs mean more marked effect. This paper focuses on the derivation of the applied input excitation and output response characteristics in the circular frequency domain for piezoelectric cantilever triple-layer benders (PCTBs), taking into account the secondary piezoelectric effect. Analytic dynamic descriptions of such actuators and transducers are obtained. Based on the presented models dynamic features of PCTB composed of PZN-8%PT are calculated, and numerical results coincide with simulations using the finite element method (FEM).