Hasil untuk "Electricity and magnetism"

D. Griffiths

In this new edition of the standard undergraduate textbook on electricity and magnetism, David Griffiths provides expanded discussions on topics such as the nature of field lines, the crystal ambiguity, eddy currents, and the Thomson kink model. Ideal for junior and senior undergraduate students from physics and electrical engineering, the book now includes many new examples and problems, including numerical applications (in Mathematica) to reflect the increasing importance of computational techniques in contemporary physics. Many figures have been redrawn, while updated references to recent research articles not only emphasize that new discoveries are constantly made in this field, but also help to expand readers' understanding of the topic and of its importance in current physics research.

G. Temple

Chaofan Wang, Kaiyi Tian, Haochen Zuo et al.

Abstract The low temperature flow properties of synthetic esters were investigated based on molecular dynamics simulations, and the influence of the molecular structure of pentaerythritol esters on the pour point was explored. When the carbon number and parity of the ester chain are the same, the pour point of the ester with a branched chain is relatively low. The pour point is related to the position of the branched chain, which near the ester group or methyl group is slightly less effective in reducing the pour point than in the β‐C position. When the number of carbons in the ester chain increases from an even to an odd number (from 6 to 7, or from 8 to 9), the pour point rises by approximately 14.5°C (from −47.65°C to −33.15°C) or 9.5°C (from −9.65°C to −0.15°C). When the number of carbons increases from odd to even numbers (from 7 to 8, or from 9 to 10), the pour point rises by approximately 23.5°C (from −33.15°C to −9.65°C) or 15.5°C (−0.15°C to 15.35°C). The branched‐chain modification method for reducing the pour point of pentaerythritol ester has been proposed. The pour point of the pentaerythritol ester was −40°C when the percentage of branched chain acid in the raw material was 10% and 15%.

Zhiyi Li, Yuzhu Tang, Zhifan Zhao et al.

Magnetoelectric dipoles have attracted global research attention due to its broadband, unidirectional, and high front-to-back ratio characteristics. This study implemented a co-simulation between a basic magnetoelectric dipole and its front feeding circuit through the step-by-step numerical extraction of its equivalent circuit model equipped with lumped and frequency-independent components. First, the series resonance subcircuit was derived from the series resonance point in the impedance of the magnetoelectric dipole. Second, the parallel resonance sub-circuit was achieved based on the parallel resonance point. By combining the series and parallel sub-circuits according to the sequence of their resonance frequency, the final form of the equivalent circuit for the basic magnetoelectric dipole was realized. Furthermore, to obtain the component values of the proposed circuit, a numerical fitting technique was adopted to accurately match the input impedance of the antenna and its equivalent circuit. A comparison of the circuit and antenna electromagnetic simulations showed that they agreed well with each other. Hence, the correctness and feasibility of the extraction process were verified. The overall results showed that the proposed circuit model can easily substitute for a basic magnetoelectric dipole in the implementation of antenna/circuit co-simulation in circuit simulators.

Shanshan SHI, Ran FENG, Chen FANG et al.

As the locational marginal pricing mechanism is hard to guarantee the real bidding of productive microgrids, the market efficiency may be decreased as a result. Considering the frequent occurence of transmission line conges-tion, this paper proposes a competitive trading mechanism for microgrid group considering congestion cost allo-cation and fair distribution. Based on the Vickrey-Clarke-Groves (VCG) theory, a payment model that promotes the real bidding of microgrids is proposed. Since the inherent problem of the VCG mechanism is the budget im-balance, and the existence of congestion in the system worsens this imbalance, this paper proposes a method to deal with the system budget imbalance based on the responsibility sharing method, in which the congestion cost is shared according to the impact of microgrid on the congestion, and the remaining system budget imbalance excluding the congestion cost is shared among consumption-oriented microgrids. The simulation results have ful-ly verified the effectiveness of the proposed mechanism.

Mahjabeen Fatima, Saleem Ayaz Khan, Syed Rizwan

The work reports nonmagnetic behavior (0.04 $μ$B) in two-dimensional (2D) V2C-OF MXene and ferromagnetism in MnO$_2$ adsorbed V2C-OF MXene. The density functional theory (DFT) calculations were carried out to study the magnetic moments of V$_2$C-OF and MnO$_2$@V$_2$C-OF MXene. The MXene, which is derived from the exfoliation of its parent V$_2$AlC MAX phase, shows a good potential to be a ferromagnetic when MnO$_2$ is adsorbed on it. The V$_2$C MXene and MnO$_2$ adsorbed V$_2$C MXene were successfully synthesized, as characterized using X-ray diffraction, showing an increased c-lattice parameter from 22.6Å to 27.2Å after MnO$_2$ adsorption. The DFT study confirmed that MnO$_2$ adsorbed V$_2$C MXene changed from nonmagnetic (in V$_2$C MXene) to a strong ferromagnetic with a magnetic moment of 4.48$μ$B for Mn adsorbed V$_2$C-OF MXene. The current work is a step-forward towards understanding of magnetism in two-dimensional materials for future 2D spintronics.

Andrea Botteon

Diffuse synchrotron emission in the form of radio halos and radio relics probe the existence of relativistic electrons and magnetic fields in galaxy clusters. These nonthermal components are generated from the dissipation of kinetic energy released by turbulence and shocks injected in the intracluster medium (ICM) during the large-scale structure formation process. By using the deepest images ever obtained on a galaxy cluster at low-frequency (72 h LOFAR-HBA + 72 h LOFAR-LBA), in arXiv:2211.01493 we provided an unprecedented view of the distribution of relativistic electrons and magnetic fields in the far outskirts of Abell 2255. In particular, we observed pervasive radio emission that fills the entire cluster volume and extends up to the cluster virial radius, reaching a maximum projected linear size of 5 Mpc. By combining radio and X-ray observations with advanced numerical simulations, we estimated the magnetic field and energy budget associated to turbulent motions at such large distances from the cluster center. Our results suggest an efficient transfer of kinetic energy into nonthermal components in the extremely diluted cluster outskirts. In the past two years, the total LOFAR-HBA observation time on Abell 2255 has increased to 336 hours. The analysis of this ultra-deep dataset aims to further advance our understanding of relativistic electrons and magnetic fields in cluster peripheries.

Gaoya Dong, Xiaolong Yang, Yunnan Fang et al.

Abstract This article presents a dual‐band filtering power amplifier (DB‐FPA) with extended passband bandwidths and wide stopband rejection, which is helpful in reducing the number of microwave components in the dual‐band radio frequency front end, resulting in compact circuit size and low loss. In the designed DB‐FPA, a wideband low‐pass filter is applied as the input matching network (IMN) to provide wideband impedance matching and good stopband rejection, while a dual‐band filtering impedance transformation is adopted as the output matching network (OMN) to provide dual‐band impedance matchings and filtering responses simultaneously. Specifically, the IMN is constructed by high‐impedance transmission‐line sections and low‐impedance open‐circuit stubs. The OMN is designed based on the specific external quality factors and coupling coefficients during two bands, resulting in dual‐band impedance transformations and dual‐band filtering responses. Then, based on the above IMN and OMN, the design procedure of the presented DB‐FPA is summarised. To verify the proposed idea, a novel DB‐FPA has been fabricated and measured. During the two frequency bands, the measured maximum power added efficiencies are 55.11% and 47.78% within 33.0 dBm input power, while the measured peak gains are 15.4 and 14.0 dB within 15.0 dBm input power.

Pedro Moura, Anand Mohan, Sophia Lau et al.

Transportation electrification can significantly reduce carbon footprint and accelerate the modernization of aging electric infrastructure. In the U.S., the growing adoption of electric vehicles (EVs) will significantly impact the electrical grid and associated greenhouse gas emissions, but with significant differences between the balancing regions due to the diverse characteristics of their electrical grids. This work assesses the impacts associated with the increasing penetration of EVs in the U.S., considering the characteristics of the grid in the different regions, in order to discuss the needed strategies to maximize the future decarbonization benefits. The assessment considers the variation in generation mix profiles during the day in each region, as well as different charging profiles associated with home, work, and public charging. The results show that more ambitious policies for the increasing share of carbon-free generation in the regions with the highest emissions are needed, emphasizing incentives for the use of work and public charging, and ensuring effective management of the charging flexibility.

Che LIU, Kaiqiao YANG, Jianghan BAO et al.

Since the introduction of Maxwell’s equations in the 19th century, computational electromagnetics has dramatically increased development. This growth can be attributed to the evolution of numerical algorithms, such as the finite difference method, finite element method, method of moments, and high-frequency approximation methods. These numerical techniques have become a crucial foundation of modern electronic and information engineering. Artificial intelligence has recently witnessed considerable development in electromagnetics; the rapid growth within this field owes itself to its robust modeling and inferential capability. This advancement has given rise to the emerging field of intelligent electromagnetic computing, which has captured the attention of numerous researchers. Remarkable achievements include electromagnetic modeling and simulation, analysis and synthesis of new electromagnetic materials and devices, and detection and perception. These contributions have injected fresh insights into the realm of electromagnetics. This paper discusses recent advances in intelligent electromagnetic computing to highlight new perspectives and avenues in research in this emerging field.

Limin Hou, Changxiao Li, Xinjian Wang et al.

With the increasing demand of high-power and pulsed power electronic devices, environmental-friendly potassium sodium niobate ((Na[Formula: see text]K[Formula: see text])NbO3, KNN) ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density ([Formula: see text]). Nevertheless, the dielectric loss also increases as the external electric field increases, which will generate much dissipated energy and raise the temperature of ceramic capacitors. Thus, an effective strategy is proposed to enhance the energy storage efficiency ([Formula: see text]) via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na[Formula: see text]K[Formula: see text])-NbO3–0.1Bi(Zn[Formula: see text](Nb[Formula: see text]Ta[Formula: see text])[Formula: see text])O3 ceramics. On the one hand, the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short–range polar nanoregions (PNRs), resulting in the high [Formula: see text]. On the other hand, the introduction of Ta ions could boost the intrinsic band energy gap and thus improve the [Formula: see text]. As a result, high [Formula: see text] of 3.29 J/cm3 and ultrahigh [Formula: see text] of 90.1% at the high external electric field of 310 kV/cm are achieved in [Formula: see text] = 0.5 sample. These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.

Manuel Sierra Castañer, Stefania Monni, Oscar Quevedo‐Teruel

Enmin Wang, Sheng Zhang, Ciyao Wang et al.

Abstract In this study, conductive polyaniline (PANI) ribbons were introduced to a semiconductive layer to improve the conductivity stability of the layer during thermal expansion and enhance its ability to inhibit charge injection into the insulating layer. To maximise the effect of PANI, PANI and carbon black (CB) were preformed into a uniformly dispersed composite, which was then added to the polymer matrix of the semiconductive layer. The experimental results show that the resistivity of the semiconductive layer containing the PANI/CB composite is more stable during thermal expansion than that of the semiconductive layer only doped with CB. This is attributed to the conductive CB network being enhanced by the PANI ribbons. In addition, due to the unique conductivity mechanism and high dielectric constant of PANI, the semiconductive layer has a strong ability to inhibit space charge injection into the insulating layer.

M. K. Akkaya, A. E. Yilmaz, M. Kuzuoğlu

Electromagnetic waves present very interesting features while the permittivity of the environment approaches to zero. This property known as ENZ (Epsilon Near Zero) has been analysed with the perturbation approach-asymptotic analysis method. Wave equations have been solved by space transformation instead of phasor domain solution and the results compared. Wave equation is non-dimensionalised in order to allow asymptotic series extension. Singular perturbation theory applied to the Wave Equation and second order series extension of electromagnetic waves have been done. Validity range of the perturbation method has been investigated by modifying parameters.

Jian-sheng LIN, Li-jia WANG

The left myocardium is the strongest cardiac muscle, representing the ability of heart to pump arterial blood throughout the body. Quantitative analysis of the contractive motion of left ventricle (LV) stands an important approach to diagnose cardiovascular diseases such as myocardial infarction. This paper utilized a biomechanical model describing the material of left myocardium to reconstruct the displacement field of LV. The mechanical model was used as an interpolation term, which was incorporated into the Bayesian estimation framework with the displacement field observed by cardiac cine magnetic resonance (CCMR) image, and the equation of displacement field was solved by finite element method. Functional parameters of LV were compared between the weak (46 cases) and normal (55 cases) ejection fraction groups of LV in the experiment. Significant differences in radial and circumferential displacement and velocity, strain and strain rate were observed between the two groups (p < 0.001), which proved that the method could effectively distinguish whether the motion of LV is normal or not. The experimental results are also highly correlated with the functional parameters of LV measured by CVI software, indicating that the method will facilitate the diagnosis of cardiovascular diseases.

Xiwen LIU, Zhuoyin PENG, Xinqiang HU et al.

Fuel cost accounts for 60%–70% of the production cost of a power plant, and the management of fuel cost has a direct influence on the power plant’s economic benefits. At present, the thermal power plants in China have attached great importance to the whole process of fuel cost management. Based on the relationship among fuel purchase cost, inventory cost and loss cost, an annual fuel cost minimization decision model is established for thermal power plants. The actual operation data of a power plant in 2019 was calculated for decision making. The results show the decision in fuel purchase timing and purchase volume reduced the total annual fuel cost, the annual fuel procurement cost, and the annual fuel inventory and loss cost by 1.18%, 1.14% and 1.43%. respectively. The proposed model provides a new method for scientific management of the fuel cost in thermal power plants.

Hiroshi Imamura, Hiroko Arai, Rie Matsumoto et al.

Recent advances in experimental techniques have made it possible to manipulate and measure the magnetization dynamics on the femtosecond time scale which is the same order as the correlation time of the bath degrees of freedom. In the equations of motion of magnetization, the correlation of the bath is represented by the non-Markovian damping. For development of the science and technologies based on the ultrafast magnetization dynamics it is important to understand how the magnetization dynamics depend on the correlation time. It is also important to determine the correlation time experimentally. Here we study the precession dynamics of a small magnet with the non-Markovian damping. Extending the theoretical analysis of Miyazaki and Seki [J. Chem. Phys. 108, 7052 (1998)] we obtain analytical expressions of the precession angular velocity and the effective damping constant for any values of the correlation time under assumption of small Gilbert damping constant. We also propose a possible experiment for determination of the correlation time.

J. Coey

Shiyan JIANG, Yanqing WANG, Yuefeng XU et al.

Investigation and study of the influencing factors for power grid safety events and their controlling measures has become a hot issue to prevent power grid safety events. In order to reveal the mechanism of power grid safety events, an analysis is made of the key cause factors for power grid safety events in China by means of qualitative analysis and grey correlation analysis based on accident causation theory. It is found that the influencing factors for power safety events mainly include subject factors(cognitive factor, behavior factor and physical factor), process factors(organization atmosphere factor and organization process factor), object factors (low equipment reliability factor and lax equipment management factor) and situational factors(operational factor and non-operational environmental factor). Grey correlation analysis shows that the cause factors for power grid events can be divided into red risk factor (r≥0.8), orange warning factor (0.7≤r＜0.8) and yellow pre-warning factor (r＜0.7), of which the factors of organization atmosphere factor, cognitive factor and behavior factor are the key cause factors for power grid events. In the end, some policy proposals are put forward for power grid safety event management to strengthen power grid safety in China.

Meng Huang, Haoran Wang, Liangjun Bai et al.

Abstract The insulated gate bipolar transistor (IGBT) is one of the most fragile components in power electronics converters. In order to improve the reliability of IGBTs, various measurements are taken according to the condition monitoring (CM) technique. Traditional CM techniques include the measurement and estimation of the device operation conditions. Recently, emerging techniques have been developed, not only for the detection and estimation but also for the prognostics of IGBTs with the condition data. In this paper, a review is performed on the recent progress in the CM techniques for IGBTs. First, some emerging electrical and thermal measurements are reviewed. Based on the sensed data, the health indicator estimation techniques are summarised. Moreover, for the emerging prognostics and health management applications, some remaining using lifetime (RUL) prediction methods are reviewed. Finally, the research gaps and directions are discussed for the CM in IGBT applications.