Hasil untuk "Electricity and magnetism"

A. Morjane, J. -G. Malherbe, J. -J. Alonso et al.

The study of the response of magnetic nanoparticles (MNP) assemblies to an external alternating magnetic field is of great interest for applications such as hyperthermia. The key quantity here is the complex susceptibility and its behavior in terms of temperature and frequency. From a theoretical point of view it can be obtained by Monte Carlo (MC) simulation with the time quantified Monte Carlo (TQMC) method if a physical time is associated with the MC step. Here we revisit this method by showing that the time unit can be derived from the MC stochastic process of the isolated particle. We first obtain a MC unit of time from the relaxation of the system at fixed temperature. Then this unit of time is used to compute complex susceptibilities. We show that it is now possible to match the TQMC results with actual experimental results regarding frequency dependent in phase susceptibilities and quantify the unit of time in seconds. Finally we show that the time unit obtained for the isolated particle remains valid when considering interacting particles such as the Heisenberg coupling or dipole dipole interactions.

Hongbo LUO, Shiyao QIN, Zixuan GUO et al.

Large-scale wind power bases typically adopt UHVAC/UHVDC transmission systems for power export, with weak grid strength in the collection area. After short-circuit faults, transient overvoltage issues are prone to occur, making it urgent to study the analytical model of transient overvoltage during short-circuit faults in wind turbine generators. Firstly, a transient voltage model after a symmetrical short-circuit fault at the remote end of the transmission line in a weak grid is established based on the typical control and voltage ride-through strategies of permanent magnet synchronous generator wind turbines. By studying the transient voltage components at the grid connection point corresponding to the voltage at the fault point, it is revealed that transient overvoltage may occur at the grid connection point after the instantaneous recovery of the fault point voltage. Secondly, a second-order simplified model suitable for transient overvoltage analysis is proposed, and clarify that the damping ratio of the simplified model is a key factor determining the peak overvoltage value. The expression of peak overvoltage is solved through time-domain analysis, and the influencing factors of transient overvoltage are quantitatively analyzed. Finally, relying on the control hardware-in-the-loop real-time simulation experimental platform, the applicability of the proposed simplified transient overvoltage model and the dominant influencing factors of transient overvoltage are verified.

Feng Bin, Fan Hou, Da Chen et al.

Abstract Porcelain insulator is an important component of power transmission systems, and its condition detection is essential to ensure safe operation of the power grid. Nevertheless, it is difficult for existing detection models to effectively solve the contradiction between detection accuracy and resource consumption. To address this issue, a high‐precision lightweight insulator defect detection model (BCM‐YOLO) based on an improved YOLOv8 is proposed. Firstly, bidirectional feature pyramid network (BiFPN), with a simplified bidirectional information flow mechanism, is employed to replace the path aggregation network with feature pyramid network in YOLOv8 to alter the feature fusion mode, thereby reducing the model size. Secondly, a cross‐stage partial Bottleneck with 2 convolutions partially replaced by a context‐guided block (C2f_CG) structure with parameter sharing is designed using the improved context‐guided block to optimise the cross‐stage partial Bottleneck with 2 convolutions (C2f) modules, thus further decreasing the number of model parameters. Finally, multiscale dilated attention is introduced into the BiFPN network to enhance the perception ability of different scales of features to improve the detection performance. Experimental results indicate that compared to YOLOv8s, the BCM‐YOLO model reduces the number of parameters by 50.5%, lowers floating‐point operations by 31.3% and increases mean average precision at intersection over union = 0.5 (mAP0.5) by 2.8%. The proposed model not only improves detection accuracy but also decreases parameter counts, making it more suitable for deployment on edge devices.

Nestor Julian Bernal-Carvajal, Carlos Arturo Mora-Peña, Oscar Danilo Montoya

This paper addresses the economic–environmental dispatch (EED) problem in DC power grids integrating thermoelectric and photovoltaic generation. A multi-objective optimization model is developed to minimize both fuel costs and CO₂ emissions while considering power balance, voltage constraints, generation limits, and thermal line capacities. To overcome the non-convexity introduced by quadratic voltage products in the power flow equations, a convex reformulation is proposed using second-order cone programming (SOCP) with auxiliary variables. This reformulation ensures global optimality and enhances computational efficiency. Two test systems are used for validation: a 6-node DC grid and an 11-node grid incorporating hourly photovoltaic generation. Comparative analyses show that the convex model achieves objective values with errors below 0.01% compared to the original non-convex formulation. For the 11-node system, the integration of photovoltaic generation led to a 24.34% reduction in operating costs (from USD 10.45 million to USD 7.91 million) and a 27.27% decrease in CO₂ emissions (from 9.14 million kg to 6.64 million kg) over a 24 h period. These results confirm the effectiveness of the proposed SOCP-based methodology and demonstrate the environmental and economic benefits of renewable integration in DC networks.

Pei Wang, You-Quan Li

We present a phenomenological model for magnetoelectricity in multiferroic materials. The distinctive feature of the model is a two-component complex order parameter that encodes the electric polarization, along with a direct coupling between the polarization and magnetic field. Our model effectively elucidates that a sufficiently strong magnetic field can destroy electric polarization. Furthermore, the transition field strength diminishes with rising temperature, following a power-law relation with the exponent being precisely worked out. At lower field strength, the electric polarization takes a spiral order in the magnetic field, with the spiral wavelength inversely proportional to the magnetic field strength. We anticipate these predictions can be experimentally tested in future studies on multiferroic materials.

Yiyuan Chen, Xiaoxiong Liu, Hai-Zhou Lu et al.

Switching magnetism using only electricity is of great significance for industrial applications but remains challenging. We find that, altermagnetism, as a newly discovered unconventional magnetism, may open an avenue along this effort. Specifically, to have deterministic switching, i.e., reversing current direction must reverse magnetic structure, parity symmetry has to be broken. We discover that, due to their symmetry which depends on chemical environments, altermagnet devices may naturally carry the parity symmetry breaking required for deterministic electrical switching of magnetism. More importantly, we identify MnTe bilayers (Te-Mn-Te-Mn-Te) as candidate devices, with the help of symmetry analysis, first-principles calculations, and magnetic dynamics simulations. This scheme will inspire further explorations on unconventional magnetism.

Maricarmen A. Winkler, Víctor Muñoz, Felipe A. Asenjo

Nonlinear effects in the propagation of perturbations in a dusty electron-ion plasma are studied, considering fully relativistic wave motion. A multifluid model is considered for the particles, from which a KdV equation can be derived. In general, two different soliton solutions are found depending on the kind of dispersion of the KdV equation. We study when the dispersion coefficient of this equation is positive. In this case, two kinds of behavior are possible, one associated with a slow wave mode, another with a fast wave mode. It is shown that, depending on the value of the system parameters, compressive and/or rarefactive solitons, or no soliton at all, can be found and that relativistic effects for ions are much more relevant than for electrons. It is also found that relativistic effects can strongly decrease the soliton amplitude for the slow mode, whereas for the fast mode they can lead to compressive-rarefactive soliton transitions and vice versa, depending on the dust charge density in both modes.

F. Napoli, J.-Y. Guan, C.-A. Arnaud et al.

<p>Amide-proton-detected magic-angle-spinning NMR of deuterated proteins has become a main technique in NMR-based structural biology. In standard deuteration protocols that rely on D<span class="inline-formula">₂</span>O-based culture media, non-exchangeable amide sites remain deuterated, making these sites unobservable. Here we demonstrate that proteins produced with a H<span class="inline-formula">₂</span>O-based culture medium doped with deuterated cell lysate allow scientists to overcome this “reprotonation bottleneck” while retaining a high level of deuteration (ca. 80 %) and narrow linewidths. We quantified coherence lifetimes of several proteins prepared with this labeling pattern over a range of magic-angle-spinning (MAS) frequencies (40–100 kHz). We demonstrate that under commonly used conditions (50–60 kHz MAS), the amide <span class="inline-formula">¹</span>H linewidths with our labeling approach are comparable to those of perdeuterated proteins and better than those of protonated samples at 100 kHz. For three proteins in the 33–50 kDa size range, many previously unobserved amides become visible. We report how to prepare the deuterated cell lysate for our approach from fractions of perdeuterated cultures which are usually discarded, and we show that such media can be used identically to commercial media. The residual protonation of H<span class="inline-formula"><i>α</i></span> sites allows for well-resolved H<span class="inline-formula"><i>α</i></span>-detected spectra and H<span class="inline-formula"><i>α</i></span> resonance assignment, exemplified by the de novo assignment of 168 H<span class="inline-formula"><i>α</i></span> sites in a 39 kDa protein. The approach based on this H<span class="inline-formula">₂</span>O/cell-lysate deuteration and MAS frequencies compatible with 1.3 or 1.9 mm rotors presents a strong sensitivity benefit over 0.7 mm 100 kHz MAS experiments.</p>

Kotaro Shimizu, Shun Okumura, Yasuyuki Kato et al.

The emergent electric field (EEF) is a fictitious electric field acting on conduction electrons through the Berry phase mechanism. The EEF is generated by the dynamics of noncollinear spin configurations and becomes nonzero even in one dimension. Although the EEF has been studied for several one-dimensional chiral magnets, most of the theoretical studies were limited with respect to the strength and direction of the magnetic fields. Furthermore, the effect of edges of the system has not been clarified, whereas it can be crucial in nano- and micro-scale samples. Here, we perform a theoretical study on the momentum-frequency profile of the EEF in a one-dimensional chiral magnet while changing the strength and direction of the magnetic field for both bulk and finite-size chains with edges. As the bulk contributions, we find that the EEF is resonantly enhanced at the magnetic resonance frequencies; interestingly, the higher resonance modes are more clearly visible in the EEF response than in the magnetic one. Furthermore, we show that the EEF is amplified along with the solitonic feature of the spin texture introduced by the static magnetic field perpendicular to the chiral axis. We also show that the static magnetic field parallel to the chiral axis drives the EEF in the field direction, in addition to much slower drift motion in the opposite direction associated with the Archimedean screw dynamics, suggesting a DC electric current generation. As the edge contributions, we find additional resonance modes localized at the edges of the system that are also more clearly visible in the EEF response than the magnetic one. Our results reveal that the emergent electric phenomena in one-dimensional chiral magnets can be tuned by the magnetic field and the sample size, and provide not only a good probe of the magnetic resonances but also a platform for the applications to electronic devices.

Wei Chen, Zhiming Liu, Huilin Zhou et al.

Abstract A novel 2‐D beam steering technology using a Fabry–Pérot antenna with a liquid‐based reconfigurable metasurface is presented. The antenna employs a reconfigurable partially reflecting surface to regulate phase distribution and adopts a microstrip antenna as feed to realise 2‐D beam steering. The antenna beam can be tilted in four different directions by injecting liquid metal into the specific area of the microfluidic channels embedded in the metasurface. Moreover, the antenna has a simple and compact structure with a low profile. A prototype is manufactured, and good agreement between simulated and experimental results verifies the correctness of the design. The measured results of the manufactured antenna prototype demonstrate that the main beam tilts to maximum values of ±15° and ±28° in the yoz and xoz planes, respectively, between 9.5 and 9.7 GHz.

Ralph M. vanSchelven, Marco Spirito, Daniele Cavallo

Abstract In this study, an efficient power combiner for mm‐wave frequency transmitters is investigated. The combiner is based on a parallel plate waveguide (PPW) excited with multiple parallel feeds. The Doherty power combiner scheme is also integrated in the proposed concept, to increase the efficiency of the amplifiers when implementing amplitude modulation. The advantage of the proposed PPW combiner with respect to other concepts, for example, the ones based on substrate‐integrated waveguide, is the wider bandwidth and the scalability to an arbitrary number of inputs. Measured results from a demonstrator realised in standard printed circuit board technology are presented. Two variations of the combiner are implemented, one terminated with a 50 Ω coaxial output, and another integrated with an antenna. In the latter case, the waveguide is folded so that both the power combiner and the antenna fit within a half wavelength size, and thus would be compatible with a dense antenna array implementation.

J. F. Nossa, M. F. Islam, Mark R. Pederson et al.

Frustrated triangular molecular magnets are a very important class of magnetic molecules since the absence of inversion symmetry allows an external electric field to couple directly with the spin chirality that characterizes their ground state. The spin-electric coupling in these molecular magnets leads to an efficient and fast method of manipulating spin states, making them an exciting candidate for quantum information processing. The efficiency of the spin-electric coupling depends on the electric dipole coupling between the chiral ground states of these molecules. In this paper, we report on first-principles calculations of spin-electric coupling in $\{V_3\}$ triangular magnetic molecule. We have explicitly calculated the spin-induced charge redistribution within the magnetic centers that is responsible for the spin-electric coupling. Furthermore, we have generalized the method of calculating the strength of the spin-electric coupling to calculate any triangular spin 1/2 molecule with $C_3$ symmetry and have applied it to calculate the coupling strength in $\{V_{15}\}$ molecular magnets.

B. Gralak, Y. Liu, S. Guenneau

We extend results of [Liu et al. Proc. Roy. Soc. Lond. A 469, 20130240, 2013] on artificial magneto-electric coupling and magnetism in moderate contrast dielectric layered media via high-order homogenization to the three-dimensional setting. For this, we consider asymptotic expansions in the vector Maxwell system. We then illustrate effect of magneto-electric coupling with numerical simulations for a layered system alternating positively and negatively refracting index. We unveil hyperbolic behaviour and magneto-electric coupling and derive a sharper estimate for the anisotropic effective medium in [Ramakrishna et al., J. Mod. Optics, 50, 1419-1430, 2003]. We also revisit the effective medium description of a PT-symmetric layered structure in [Novitsky, Shalin, Novitsky, Phys. Rev. A 99, 043812, 2019], adding higher-order approximation orders.

Xiaosi Lin, Wah Hoon Siew, John Liggat et al.

Abstract This work reports the effect of octavinyl polyhedral oligomeric silsesquioxane (OvPOSS) on tuning the electrical performance of polypropylene (PP). OvPOSS with different content are introduced into PP using the solution method. The microstructural morphology, crystallinity behaviour, breakdown strength, DC conductivity, space charge formation, and trapping level distribution are measured. The results indicate that the OvPOSS nanofiller can be dispersed uniformly with a doping content of 2.0 phr or less. The DC conductivity is decreased, and the breakdown strength of OvPOSS/PP nanocomposites is significantly increased. The space charge accumulation of the OvPOSS/PP nanocomposites is significantly suppressed due to the introduction of deeper traps by the OvPOSS nanofiller. Finally, the experimental results demonstrate that the OvPOSS nanofiller can greatly increase the electrical performance of the base PP and the OvPOSS/PP nanocomposites have much potential for HVDC applications. They further demonstrate that the PP is environmental‐friendly due to its thermo‐plastic property, which can be recycled after the manufacture.

Yan Lin, Ru Wang, Jiawei Qu et al.

Considering the advantages of high Curie temperature and environment-friendly nature of KNN piezoelectric ceramics, the limitation of weak piezoelectric response and their temperature sensitivity to applications is worth exploring. Herein, the <001> textured (1-[Formula: see text])(K[Formula: see text]Na[Formula: see text])(Nb[Formula: see text]Sb[Formula: see text])O3-[Formula: see text](Bi[Formula: see text]Na[Formula: see text])HfO3([Formula: see text] = 0.01−0.045) lead-free ceramics were synthesized by templated grain-growth method. The high piezoelectric performance (d[Formula: see text] of 474 pC/N and strain of 0.21%) and excellent temperature stability (unipolar strain maintained within 4.3% change between 30[Formula: see text]C and 165[Formula: see text]C) were simultaneously achieved in the textured KNNS-0.03BNH ceramics. The high piezoelectric performance can be attributed to the summation of the crystallographic anisotropy and phase structure contributions in <001> textured ceramics. The superior temperature stability of piezoelectric properties can be interpreted by the contribution of crystal anisotropy to piezoelectric properties reduces the effect of phase transition on piezoelectric properties deterioration. This study provides an effective strategy for simultaneously achieving high piezoelectric properties and superior temperature stability in KNN-based textured ceramics.

Yanxin Li, Zhuo Wang, Menglei Kong et al.

Abstract In order to adapt to the development of electronic devices, it is necessary to improve the thermal conductivity and breakdown strength of composites. Boron nitride (BN) is an ideal candidate material with high breakdown strength and thermal conductivity. Therefore, the introduction of BN nanosheets into the polyvinylidene fluoride (PVDF) matrix can improve the thermal conductivity and breakdown strength of the composites at the same time. However, BN nanosheets can easily agglomerate in the matrix, which limits the improvement of the properties of the composites. To overcome this difficulty, appropriate water‐bath heating was used to improve the fluidity of PVDF. Therefore, the dispersion of the filler is improved. When the volume fraction of BN nanosheets is 3% and the preparation temperature is 45°C, the energy storage density of the composites reached 18.5 J/cm3 at 540 kV/mm. At this point, the thermal conductivity was 0.49 W/(m⋅K), 3.5 times that of the pure PVDF film.

Qinan LI, Yongjun XIA, Xiaolin ZHANG et al.

In MMC impedance modelling, the existing research does not take into account the influence of the capacitive voltage transformer (CVT) measurement characteristics on the mid and high frequency bands of the MMC impedance, which may reduce the accuracy of the stability analysis of the flexible HVDC transmission system. By taking the south channel unit of the Yu’E flexible HVDC project as the research object, and based on an analysis of the influence of stray capacitance on the measurement characteristics of a 500kV fast saturated CVT, a MMC impedance modelling method is proposed using the multi-harmonic linearization method. The impedance analysis method is used to analyze the influence of the CVT broadband measurement characteristics on the stability of the HVDC system when the MMC station is connected to different AC systems and operates at different steady-state operating points. The results show that the CVT broadband measurement characteristics will cause the oscillation frequency of the system to change under certain working conditions. Through PSCAD/EMTTDC simulation, it is verified that the proposed MMC impedance model, which takes into account the CVT broadband measurement characteristics, can improve the accuracy of the stability analysis of the flexible HVDC system.

Ivan A. Starkov, Mikhail A. Mishnev, Alexander S. Starkov

This paper presents a theoretical model for describing the thermodynamic properties of doped ferroelectric crystals based on a modified Weiss mean-field approach. Accounting for quadrupole and octupole terms in the expression for the effective field within the Weiss model makes it possible to move from the Langevin equation to the Landau–Ginzburg equation. Furthermore, the coefficients of the Landau–Ginzburg equation can be expressed in terms of the physical parameters of the crystal lattice. For these parameters, analytical expressions are proposed that describe their change when adding dopants in ceramic matrix composites. Perovskite barium titanate ceramics with a variety of inclusions is considered as an application example of the developed method. The obtained agreement between the analytical and experimental results for barium titanate ceramics with lanthanum/magnesium/zirconium dopants gives us hope of the applicability of the present theory to the calculation of other doped ferroelectrics as well.

Rafael Gonçalves Licursi de Mello, Anne Claire Lepage, Xavier Begaud

Abstract The simple planar shape and wideband input impedance of the bow‐tie antenna make it suitable to diverse wideband applications. However, the radiation pattern of this kind of antenna is not stable and the gain in the broadside direction deteriorates with increasing frequencies. In this article, the operation of both the triangular and the rounded‐edge versions of the bow‐tie antenna is thoroughly investigated and the performance thereof is compared. A technique to maximise such performance, which consists of inserting radially aligned grooves in the radiators' ends, is presented. The bandwidth, defined by a broadside gain of at least 2 dBi and a reflection coefficient magnitude of less than −10 dB, is improved from 85.7% to 97.9% in simulations. Such an improvement is validated through the measurement of two prototypes, in which the presented technique also increases the broadside gain in up to 1.5 dB, with no significant change in the shapes of the radiation patterns and in the reflection coefficient magnitude.

Shuangfeng DAI, Ze YE, Man JIANG et al.

This paper analyzes the influencing factors of the comprehensive benefits in cross-provincial power trading, constructs the measurement model and finally completes the calculation of the comprehensive benefits, which provides direction guidance for cross-provincial power trading. The results show that in the cross-provincial power trading, the comprehensive benefit depends on the arrangement of the transaction direction, multi-type power trading is significantly better than the coal-fired power trading, and the hydro-power trading have the best comprehensive benefits, which are obviously better than the thermal power transactions.