Hasil untuk "Electricity and magnetism"

Mohamed H. Abdo, El‐Sayed M. El‐Refaie, Abd Elrahman S. Tawfic et al.

ABSTRACT This study investigates the dielectric and thermal properties of transformer oil‐based nanofluids incorporating Fe3O4‐coated SiO2 core–shell nanoparticles as nanofillers. The nanoparticles were synthesised with varying shell thicknesses, and two samples underwent surface treatment. Fourier transform infrared spectroscopy was used to characterise the nanoparticles. The spectra for unmodified and modified nanoparticles detected Fe‐O bond, Si‐O‐Si bond and oleic acid existence. The nanofluids were prepared using a two‐step method: nanoparticles were first prepared at concentrations of 0.04, 0.07 and 0.10 g/L, and then mixed with the base oil and dispersed using ultrasonication. AC breakdown strength was measured for samples at these concentrations to determine the optimum concentration for each type of nanoparticle. The optimum concentration, which provided the best performance for AC breakdown voltage across all nanoparticle types, was found to be 0.07 g/L. Thermal conductivity testing was then conducted at this optimum concentration. The addition of nanofillers resulted in increased AC breakdown strength and thermal conductivity. Particle size and zeta size measurements were carried out to assess the dispersion behaviour of the nanofluid samples. The physical discussion examined potential reasons for improvements in AC breakdown voltage and thermal conductivity. Trapping and de‐trapping processes, shell thickness and surface modifications were analysed in relation to improved dielectric performance. Ballistic phonon transport and Brownian motion mechanisms were employed to explain the observed enhancements in thermal conductivity. These findings indicate the potential for developing a new class of liquid dielectrics suitable for use in power transformers.

Arvind Sundaram, Shiming Yin, Ugur Mertyurek et al.

Cheng Peng, Kaiwen Shi, Jian Deng et al.

IntroductionDuring severe accidents, the interaction of hot melt with coolant forms porous debris beds in the reactor lower head or cavity. The long-term coolability of these beds is critical for accident mitigation and reactor safety enhancement, primarily determined by the dryout heat flux (DHF). Despite existing models, gaps persist in accounting for two-phase flow dynamics and interfacial shear effects.MethodsThis study develops high-fidelity mechanistic models to address these limitations. First, classical DHF models are reviewed, identifying key assumptions requiring refinement. New models are derived by incorporating: (1) two-phase flow characteristics (e.g., relative permeability, capillary pressure) and (2) gas-liquid interfacial shear stress. These models are extended to stratified debris bed configurations. Validation is performed using experimental data from KTH's POMECO-HT (top-injection) and VTT's STYX-3.1 tests.ResultsThe two-phase flow model achieved a 20% DHF prediction error, while the interfacial shear model reduced errors to 8.9%. For stratified beds, the error further decreased to 4.5%, demonstrating superior accuracy.DiscussionThe results highlight the necessity of interfacial shear effects and stratification in DHF predictions. The proposed models offer a robust foundation for debris bed cooling analysis codes, significantly improving safety assessments.

A. Vela Wac, F. A. Gómez Albarracín, D. C. Cabra

Magnetic skyrmions, topologically stable spin textures, have attracted significant interest due to their potential applications in information storage and processing. They are typically stabilized by the Dzyaloshinskii-Moriya interaction in the presence of a magnetic field and can be manipulated by electric fields in magnetoelectric systems. Here we investigate, using Monte Carlo simulations, the behavior of skyrmions in a classical Heisenberg magnetoelectric model on the square lattice under combined magnetic and electric fields. We analyze spin and dipolar textures, structure factors, magnetization, chirality, and polarization for different field directions and magnitudes, identifying ferromagnetic, ferroelectric, spiral, skyrmion crystal, skyrmion gas, and bimeron phases, as well as the field-induced transitions between them. We find that the competition between electric and magnetic fields can destroy or transform skyrmion lattices into skyrmion-gas or bimeron phases. While magnetic fields induce chiral phases even in the presence of an electric field, electric fields strongly reshape the chiral region and deform skyrmion textures. This reciprocal influence between magnetic and electric orders reflects the intrinsic magnetoelectric coupling characteristic of multiferroic materials. Specifically, we observe the simultaneous sudden growth in magnetization with a switch-off in the polarization, typically observed in experiments. In this context, localized magnetoelectric entities, such as skyrmions carrying electric quadrupoles, exemplify the intertwined nature of spin and charge degrees of freedom, providing a microscopic basis for the control of topological states in ME systems and their potential use in spintronic applications.

Tanmay Patil, S. Shankaranarayanan

The Carrollian limit ($c \to 0$) of General Relativity provides the geometric language for describing null hypersurfaces, such as black hole event horizons and null infinity. Motivated by the well-established electric and magnetic limits of Galilean electromagnetism, we perform a systematic analysis of the low-velocity limit of linearized gravity to derive its Carrollian counterparts. Using a 1+3 covariant decomposition, we study the transformation properties of linear tensor perturbations (gravitational waves) on a Friedmann-Lemaitre-Robertson-Walker background under Carrollian boosts. We demonstrate that, analogous to the electromagnetic case, the full set of linearized Einstein's equations is not Carrollian-invariant. Instead, the theory bifurcates into two distinct and consistent frameworks: a Carrollian Electric Limit and a Carrollian Magnetic Limit. In the electric limit, dynamics are frozen, leaving a static theory of tidal forces ($E_{ab}$) constrained by the matter distribution. In contrast, the Magnetic Limit yields a consistent dynamical theory where the magnetic part of the Weyl tensor ($H_{ab}$), which governs gravito-magnetic and radiative effects, remains well-defined and is sourced by the spacetime shear. This framework resolves ambiguities in defining Carrollian gravity and provides a robust theory for gravito-magnetic dynamics in ultra-relativistic regimes. Our results have direct implications for the study of black hole horizons, gravitational memory, and the holographic principle.

Bo Zhang, Zhi Ning Chen, Yucong Zhou et al.

A henge-like metaring (HMR) is proposed for improving the radiation pattern roundness of monopole antennas off-center mounted on a finite ground by localizing the radiation from the monopole and suppressing the scattering by the ground. The improved patterns enhance uniform coverage of multiple-input and multiple-output (MIMO) systems. The study reveals that the radiation pattern of an off-center monopole is distorted by the asymmetric ground currents excited by both the feed and the radiation of the monopole. The distorted radiation patterns severely degrade wireless communication link quality. The HMR, composed of an annular array of mushroom unit cells, simultaneously functions as an electromagnetic bandgap (EBG) and a radiator, and encircles the monopole to form a henge monopole antenna (HMA). The HMR as an EBG is used to suppress the ground currents outside the HMR analyzed by an equivalent circuit model. The HMR as a radiator is designed to decouple the monopole from the ground with its elevated radiation pattern using characteristic mode analysis. As examples, two prototypes of single and four off-center MIMO HMAs are designed and investigated in the 2.45-GHz band. Simulated and measured results show that the single HMA and each of the four HMAs achieve the un-roundness of the radiation pattern at θ = 65° plane lower than 2 dB and 3 dB in the 2.45-GHz band. As a result, near the radiation nulls, the SNR is improved by 6 dB. The compact construction and efficient current suppression facilitate the application of HMAs in multi-antenna systems above a finite ground with uniform coverage and reliable connections.

Youngje Sung

In this paper, the basic structure of a quad-band substrate-integrated waveguide (SIW) antenna with filtering characteristics is proposed. The proposed antenna consists of a four-slot SIW and a single-probe feed. Despite having a single feed, it was able to independently control the four resonant frequencies. However, since a basic quad-band SIW antenna has three radiation null frequencies, the left skirt characteristics of f1 and the right characteristics of f4 were not good. To improve this, four pairs of vias and a pair of U-slots were introduced to add two radiation null frequencies to the lower part of f1 and the upper part of f4, respectively. This time, the parameters of the basic structure did not change, except for those of the added structure. The fabricated antenna operated at 3.9, 4.03, 4.2, and 4.3 GHz, and exhibited a radiation null below −15.6 dBi at 3.6, 3.95, 4.09, 4.27, and 5.07 GHz.

Zhongfei CHEN, Yue ZHAO, Qiuna CAI et al.

In the context of rapid development of renewable energy, the power system is required to keep sufficient ramping capability for coping with the renewable generation's fluctuation and intermittence. Analyzing the supply-demand situation of the power system's ramping capability can discover the risk of insufficient ramping capability and improve the security and stability of the power system operation. This paper firstly proposes the logic and procedure for power system ramping capability adequacy evaluation, and clarifies the definitions and concepts of the netload ramping capacity, uncertainty ramping capacity, surplus ramping capability and its demand-supply ratio. And the theories and specific calculation methods for estimating the netload forecast error based on the confidence statistics and quantile regression, as well as the specific calculation methods for the above parameters, are subsequently proposed. Finally, an example analysis is carried out based on the data of forty historical operating days and four typical days in Guangdong to validate the effectiveness of the proposed adequacy evaluation method. This research indicates that the surplus ramping capability demand-supply ratio can effectively identify the ramping characteristics in different typical days and special periods, reflecting the adequacy of ramping capability in the day and minute scale; the indicators such as coverage, excess, and estimation quantity can be used to evaluate the applicability of error estimation models in different regions and scenarios, serving as a reference for model selection.

Haocheng DU, Shilong LI, Yuntao JU et al.

In the large-scale multi-moment distribution network reconfiguration (DNR) problem, a large number of switches to be optimized seriously reduces the solution efficiency of distribution network reconfiguration. To address this problem, a distributional robust distribution network reconfiguration model based on a compressed switch candidate set was proposed, which was divided into two stages. The first stage took the minimization of active network loss of the system as the objective function and used the optimal matching loop flow method to compress the switch candidate set; the second stage took the minimization of the sum of the power purchase cost and the switch action cost as the objective function, constructed the chance constraints on the capacity limits of the power point, and adopted a Wasserstein ball-based distributional robust method to deal with the uncertainty of distributed generation. It transformed the model into a mixed-integer second-order conic planning problem by deterministically transforming the worst-case expectation and chance constraints in the objective function by using a dual transformation method. Finally, numerical experiments were conducted on the 33 node and Liaoning Panjin 45 node systems, which proved that the model proposed in this paper could effectively improve the computational efficiency, and the decision maker could adjust the economy and conservatism of the model by changing the number of samples and the confidence level, compared with the robust model and the stochastic planning model.

Jae-Shin Park, Jeong-Pyo Kim, Doo-Yeong Yang

In this study, we propose the wide field of view (FoV) radar module for autonomous vehicles. The proposed wide FoV radar (WFR) module was constructed using of an RF module comprising wide beamwidth microstrip patch antennas, an AWR1642 radar sensor chip, and a control module. To achieve a wide FoV of 150° using the fabricated radar module, the 3-dB beamwidth characteristic of the applied microstrip patch antenna had to wider than 150°. The patch antenna was designed using a comb-line structure along 10-by-1 array structure, each radiator characterized by a shorted patch structure, such as a planar inverted-F antenna. The designed antenna was then fabricated on the same board surface as the sensor chip. To identify the characteristics of the implemented radar module, a trihedral corner reflector with a radar-cross-section of 180 m2 was used as the reflector target, and the CA-CFAR (cell averaging constant false alarm rate) target detection algorithm was applied. The measurement results, showed good detection performance of the radar in the view angle of 150°, from −75° to +75°, and a broad bandwidth of 4 GHz in the 77–81 GHz millimeter band. Therefore, the proposed WFR is applicable for used in blind spot detection sensors in autonomous vehicles.

Merve Tascioglu Yalcinkaya, Padmanava Sen, Gerhard Fettweis

Abstract The advancement of communication and radar systems has triggered the demand for in‐band full‐duplex (IBFD) operation. IBFD is regarded as one of the most outstanding technologies in terms of its ability to improve spectral efficiency and data rate. IBFD operation has the potential not only to enable communication or radar systems separately, but to help realising radar sensing and communication at the same time, known as Joint Communication and Sensing (JC&S) technology. In realisation of IBFD and JC&S systems, self‐interference (SI) is the key challenge for antenna designers. In this article, a comprehensive survey on SI reduction techniques in the antenna domain is provided and the advantages and disadvantages of each technique are studied. SI reduction techniques have been proposed separately but an elaborated review of relevant techniques with a comparative study has not been presented yet. For the first time, a systematic comparative study of different SI reduction techniques is graphically presented to cover a comparison based on isolation, gain, and impedance bandwidth in terms of before and after SI reduction techniques. Moreover, this study also explores how antenna isolation characteristics vary with respect to the thickness and the permittivity of the substrate without any SI reduction technique.

CHEN Mengying, WU Yupeng, PANG Qifan et al.

Three-dimensional (3D) gradient recalled echo (GRE) sequence with magnetization transfer (MT) can simultaneously image neuromelanin and magnetic susceptibility. However, the sequence requires long duration of MT saturation pulse and the effect of MT pulse on susceptibility values remains unclear. Therefore, this paper aims to shorten the MT pulse duration and evaluate the effect of MT pulse on susceptibility value. Results showed that 3D GRE sequence with 5 ms of MT pulse provided a saturation effect no less than that of 8 ms, 10 ms and 12 ms in highlighting neuromelanin, and yielded susceptibility values in the deep gray matter nuclei similar to sequence without MT pulse. In conclusion, short MT pulse provides a practical means to simultaneously image the neuromelanin and magnetic susceptibility.

Alexander J. Silenko

We suppose that the covariance of Lagrangians always taking place results in a distortion of any electric and magnetic field by a pseudoscalar field of dark matter axions and axion-like particles. As a result, electric and magnetic fields acquire oscillating magnetic and electric components, respectively. The Maxwell-like equations are rigorously derived. One can also use an equivalent approach based on an introduction of effective oscillating magnetic charges and electric dipole moments in undistorted electromagnetic fields. The determined relations between the magnetic charges and electric dipole moments and the axion-photon coupling constant open a possibility to compare a sensitivity of search for axions in optical experiments and experiments with massive particles. The dual (inverse) Witten effect defining effective magnetic charges of electrically charged particles opens new exciting possibilities to search for axions and axion-like particles with very small masses in nonresonance experiments. The study of a passage of strongly decelerated electrons or positrons through a solenoid is proposed.

Antonio De Felice, Shinji Tsujikawa

We compute the quasinormal modes of static and spherically symmetric black holes (BHs) with electric and magnetic charges. For the electrically charged case, the dynamics of perturbations separates into the odd- and even-parity sectors with two coupled differential equations in each sector. In the presence of both electric and magnetic charges, the differential equations of four dynamical degrees of freedom are coupled with each other between odd- and even-parity perturbations. Despite this notable modification, we show that, for a given total charge and mass, a BH with mixed electric and magnetic charges gives rise to the same quasinormal frequencies for fundamental modes. This includes the case in which two BHs have equal electric and magnetic charges for each of them. Thus, the gravitational-wave observations of quasinormal modes during the ringdown phase alone do not distinguish between electrically and magnetically charged BHs.

by J. Urrestarazu Larrañaga, Naveen Sisodia, Van Tuong Pham et al.

Magnetic skyrmions are topological spin textures which are envisioned as nanometre scale information carriers in magnetic memory and logic devices. The recent demonstration of room temperature stabilization of skyrmions and their current induced manipulation in industry compatible ultrathin films were first steps towards the realisation of such devices. However, important challenges remain regarding the electrical detection and the low-power nucleation of skyrmions, which are required for the read and write operations. Here, we demonstrate, using operando magnetic microscopy experiments, the electrical detection of a single magnetic skyrmion in a magnetic tunnel junction (MTJ) and its nucleation and annihilation by gate voltage via voltage control of magnetic anisotropy. The nucleated skyrmion can be further manipulated by both gate voltage and external magnetic field, leading to tunable intermediate resistance states. Our results unambiguously demonstrate the readout and voltage controlled write operations in a single MTJ device, which is a major milestone for low power skyrmion based technologies.

Taher Badawy, Thomas Bertuch, Claudius Loecker et al.

Abstract A high gain vertically polarised travelling‐wave frequency scanning array antenna fed by a meander rectangular waveguide is presented for Ku‐band operation. The proposed antenna is used in a radar demonstrator setup to detect and monitor birds in direct proximity to the wind farms. The goal is to prevent collisions of birds with wind farms. The proposed antenna consists of 34 inclined dumbbell‐shaped radiating slots integrated with a parallel‐plate waveguide. The proposed meandered feeding structure is used to enlarge the beam scanning angle range over frequency. The dumbbell‐shaped radiating slots are employed in the narrow wall of the meandered waveguide due to the space restriction of the meandering. The parallel‐plate waveguide is used as a polarisation filter to reduce the cross‐polarisation level of the proposed antenna owing to the inclination of the radiating slots. An E‐plane horn is used to reduce the beamwidth in the elevation plane. The overall size of the antenna is 20.6λ in length and 15λ in width, where λ is the free space wavelength at 15.55 GHz. The antenna operates in the frequency range from 15.40 to 15.70 GHz. The half power beamwidth is about 4° in the azimuth plane and about 20° in the elevation plane at 15.55 GHz. The main beam of the antenna steers over frequency to cover 39° of angular range in the azimuth plane. A Taylor distribution is applied to achieve sidelobe level below −25 dB in the same plane and 26 dBi gain over the operating frequency range. The antenna array is fabricated and measured successfully to verify the proposed approach. The fabricated antenna shows an impedance matching significantly better than 10 dB in the operating frequency. The measured gain is higher than 25 dB throughout its frequency range.

Chen JIN, Dawei REN, Jinyu XIAO et al.

In September 2020, China proposed to striving to achieve carbon neutrality by 2060. It is an important way to achieve carbon neutrality by vigorously developing a power system with high penetration of wind and photovoltaic (PV) solar energy. Due to the fluctuating and intermittent nature of new energy power generation, it is necessary to improve the flexibility of the power system to guarantee the safe, stable and economic operation of the clean energy power system. With the 2060 carbon neutrality target as the boundary and an incorporated 8760-hour-time-series operation simulation model, we optimize the new energy power, energy storage and grid interconnection capacity from different time and space scales, considering various flexibility resources constraints, thereby offering a viable way to carbon neutrality. On this basis, the sensitivity analysis on wind and PV power curtailment, wind and PV power capacity, energy storage and grid interconnection capacity are completed to further demonstrate the effectiveness of the proposed model and method, and the benefits of coordinated supply-grid-storage planning are quantitatively analyzed for the high new energy penetrated power system.

Rasoul Fakhte, Iman Aryanian

Abstract A wideband and high gain circularly polarised patch antenna has been introduced. The proposed antenna combines an aperture coupled feeding with a T‐slot, four metallic vias and a patch with a diagonal slot to present high gain and wide 3‐dB axial ratio bandwidth (BW) characteristics. In this study, a rectangular patch (0.6 λ0 × 0.5 λ0 at f = 7.5 GHz) with a diagonal slot has been symmetrically located above the T‐slot at the height of 0.07 λ0. A WR90 waveguide with the length of 50 mm and a T‐slot in its extended outer wall has been used as a primary antenna that feeds the patch element. Four metallic vias with shunt inductive effects have been used to virtually enlarge radiating patch dimension, so they present a significant improvement in antenna gain, BW and axial ratio. The proposed antenna shows the BW of 30% with tgain of up to 12 dBi and an axial ratio BW of 21%. Due to its wideband, high gain, and wide 3‐dB axial ratio BW, this antenna is a good candidate for some applications, such as small satellites, and for the global positioning system the high gain, precision and flexibility of the system are crucial.

William Degaulle Waladi Gueagni, Lionel Tenemeza Kenfack, Martin Tchoffo et al.

The magneto-electrocaloric effect which can be defined as the coupling between magnetocaloric and electrocaloric effects attracts currently considerable attention due to the advantages provided by the caloric effect in designing solid-state refrigeration technologies. The magneto-electrocaloric effect of a multiferroic antiferromagnetic spin system with the Dzyaloshinskii Moriya (DM) interaction is investigated in this paper. The DM interaction is assimilated to a coupling between an external site-dependent electric field and a local electric polarization. The external magnetic is also considered as a site-dependent magnetic field. The spin-wave theory is used as a diagonalization method and through the canonical partition function, some thermodynamic properties such as the Boltzmann entropy and the specific heat capacity are obtained. Then, the adiabatic magnetic, electric, and magnetoelectric cooling rates are also derived. The graphs obtained for the adiabatic magnetic, electric, and magnetoelectric cooling rate show a characteristic behavior of the caloric or multi-caloric effect which is in good agreement with some experimental and theoretical works. Besides, the entropy response due to the variation of the external site-dependent magnetic field exhibits two anomalous entropy peaks indicating the existence of an intermediate phase tuneable by the magnetic and electric site-dependent parameters. Overall, it is demonstrated that the cumulative influence of the site-dependent magnetic and electric fields allows us not only to reveal quantum critical points hidden in a multiferroic quantum spin system but also to control the caloric or multi-caloric effect essential in the construction of solid-state refrigeration devices.

K. S. Denisov

The recent rise of material platforms combining magnetism and two-dimensionality of mobile carriers reveals a diverse spectrum of spin-orbit phenomena and stimulates its ongoing theoretical discussions. In this work we use the density matrix approach to provide a unified description of subtle microscopic effects governing the electron gas spin behavior in the clean limit upon electric perturbations in two-dimensional magnets with strong spin-orbit coupling. We discuss that an inhomogeneity of electrostatic potential generally leads to the electron gas spin tilting with the subsequent formation of equilibrium skyrmion-like spin textures and demonstrate that several microscopic mechanisms of 2DEG spin response are equally important for this effect. We analyze the dynamics of 2DEG spin upon an oscillating electric field with a specific focus on the emergent electric dipole spin resonance. We address the resonant enhancement of magneto-optical phenomena from the spin precession equation perspective and discuss it in terms of the resonant spin generation. We also clarify the connection of both static and dynamic spin phenomena arising in response to a scalar perturbation with the electronic band Berry curvature.