Hasil untuk "Electricity and magnetism"

Ying Liu, Jiazhu Yu, Meng Ma

ABSTRACT The ± 200 kV direct current (DC) cables of the Zhoushan Transmission Project were targeted, and crosslinked polyethylene (XLPE) insulation samples were prepared from faulty and spare cables. Samples were tested for oxidation induction period, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermally stimulated depolarisation current, space charge and DC dielectric strength. The evolution of performance parameters was analysed, and the insulation ageing characteristics of onsite operating DC cables were deduced. The results show that compared with spare cables, the carbonyl index of operating cables decreases, the crystallinity increases and DC dielectric strength increases slightly. It is inferred being related to the reduced content of antioxidants and crosslinking by‐products and improved molecular chain and crystal microstructure of XLPE insulation. It is suggested that the insulation ageing of high voltage DC XLPE cable is divided into two stages. In the early stage, the secondary crosslinking and recrystallisation processes are dominant, and the thermal and electric effects make the material properties basically stable or even slightly improved. In the middle and later stage, the thermal oxygen reaction is dominant, the microstructure of the material is destroyed, with a large number of macromolecular chains broken and some crystalline regions transformed into amorphous ones, and the insulation properties degraded significantly.

Marijn Rikers, Ayesheh Bashiri, Katsuya Tanaka et al.

We investigate the polarization properties of emission associated with the magnetic dipole and electric dipole transitions of europium(III) coupled to an anisotropic dielectric metasurface with polarization-engineered electric and magnetic photonic local density of states. The metasurface consists of a square array of Mie-resonant elliptical a-Si:H dimers situated on an SiO$_2$ substrate and embedded in a PMMA film containing Eu(TTA)$_3$. Based on reciprocity principle, it was designed to achieve maximum electric (magnetic) field enhancement in the dimer gap at 610 nm (590 nm) for $x$-polarized ($y$-polarized) normally incident light in order to selectively enhance the electric dipole (magnetic dipole) emission into the $x$-polarized ($y$-polarized) emission channel, respectively. Momentum-resolved spectroscopy and back-focal plane imaging of emission of the fabricated light-emitting metasurface clearly reveal the intended polarization-dependent emission behaviour, with the $x$-polarized ($y$-polarized) emission showing a reduced (enhanced) ratio of the magnetic-/electric dipole emission intensity, correspondingly where the magnetic dipole emission is enhanced with a magnetic field enhancement from the nanostructures. The demonstrated polarization-dependent interaction of a designed nanostructure with the electric- and magnetic dipolar transitions of trivalent lanthanide ions opens an avenue towards routing of emission of different multipolar orders into different polarization channels.

CHEN Bo, LIU Quan, MA Lei et al.

A simulation model of the CW-EPR (continuous wave electron paramagnetic resonance) system’s signal transmission, modulation, and detection is constructed using the Simulink platform. The model supports signal source simulation, modulation, detection by the Schottky diode detector, and lock-in amplifier-assisted demodulation. Using this model, we characterize how 5,5-dimethyl-1-pyrroline N-oxide (DMPO) samples’ spectra vary with modulation amplitudes and phases. Consistency is observed between the simulated and experimentally measured spectral signals over a range of modulation amplitudes and phases. The presented simulation model offers theoretical support for understanding CW-EPR phenomenon in depth, optimizing experimental parameters, and guiding CW-EPR experiments. It also provides a reference for designing and optimizing EPR systems in subsequent research.

Md Jahangir Alam, Abubakar Hamza Sadiq, Jaroslav Kristof et al.

The blood–brain barrier (BBB) limits drug delivery to the brain, particularly for large or hydrophilic molecules. Brain microvascular endothelial cells (bEND.3), which form part of the BBB, play a critical role in regulating drug uptake. This study investigates the use of cold atmospheric microplasma (CAM) to enhance membrane permeability and facilitate drug delivery in bEND.3 cells. CAM generates reactive oxygen species (ROS) that modulate membrane properties. We exposed bEND.3 cells to CAM at varying voltages (3, 3.5, 4, and 4.5 kV) and measured drug uptake using the fluorescent drug FD-150, fluorescence intensity, ROS levels, membrane lipid order, and membrane potential. The results showed a significant increase in fluorescence intensity and drug concentration in the plasma-treated cells compared to controls. ROS production, measured by DCFH-DA staining, was higher in the plasma-treated cells, supporting the hypothesis that CAM enhances membrane permeability through ROS-induced changes. Membrane lipid order, assessed using the LipiORDER probe, shifted from the liquid-ordered (Lo) to liquid-disordered (Ld) phase, indicating increased membrane fluidity. Membrane depolarization was detected with DisBAC2(3) dye, showing increased fluorescence in the plasma-treated cells. Cell viability, assessed by trypan blue and LIVE/DEAD™ assays, revealed transient damage at higher voltages (≥4 kV), with recovery after 24 h. These results suggest that CAM enhances drug delivery in bEND.3 cells by modulating membrane properties via ROS production and changes in membrane potential. CAM offers a promising strategy for improving drug delivery to the brain, with potential applications in brain-targeted therapies.

Weizhe Qu, Dongfang Zhou, Qing Liu et al.

ABSTRACT A polarisation conversion metasurface (PCM) is proposed to realise broadband radar cross section (RCS) reduction of a slot array antenna. The PCM's unit cell, whose polarisation conversion ratio (PCR) is more than 88% from 8.41 to 32.28 GHz under x‐and y‐polarised normal incidence, consists of two pairs of v‐patterns with gradually narrowing widths and a pair of rectangular patterns. The wideband RCS reduction of PCM is achieved by chessboard structure. Simulated and measured results prove that the application of PCM reduces wideband RCS. The proposed PCM can realise the RCS reduction outside the antenna's operating band. The 10 dB RCS reduction ranges from 8.7 to 34.8 GHz under normal incident wave with no polarisation insensitivity.

Savino Longo

Many applications of Neural Networks (NN) to plasma science have appeared in the last years. The author describes here some of the early applications of NNs to plasma science at the beginning of the 90 s, when multi-layer, feed-forward-back-propagation (FFBP) architectures found several applications in this field: they were used to solve inversion problems, to create complete sets of input data, to replace time-consuming modules in models and to predict the outcome of real processes. From a partially personal perspective the author reviews the details of plasma problems to which NNs were successfully applied, and those of the related architectures. It turns out that some solutions, which are perceived today as marking the difference between the previous and contemporary NNs application practices, were in common use >30 years ago when they were deemed fruitful. This can help create deeper historical insight into a field that is getting much attention today.

Devendra Kumar, Dhirendra Mathur

This paper proposes a novel design for a frequency reconfigurable and bandwidth-enhanced antenna for use in biomedical telemetry applications. Data pertaining to a patient’s body parameters, such as blood pressure, pulse, and temperature, are gathered using sensors and then transmitted to a remote place for monitoring. The proposed antenna is connected to a wearable transmitter, which transfers the body parameter data to a centrally located nearby control unit. The antenna operates in the 5.8 GHz band in single-band mode and in the 4.27 GHz (C band) and 5.8 GHz industrial, scientific, and medical (ISM) bands in dual-band mode. The use of ethylene-vinyl acetate foam as a substrate makes the structure waterproof and ultraviolet resistant. The basic antenna structure equipped with proximity coupling offers a front-to-back ratio (FBR) of 17.62 dB and a bandwidth of 122 MHz. With an additional upper patch and resonant slots, bandwidth enhancement of 82.85% and 11.57% improvement in the FBR are achieved, respectively. Overall, a maximum FBR of 19.66 dB and gain of 5.0 dBi are attained over the resonant frequency. The specific absorption rate is found to be 0.145 W/kg for 10 gram of tissue.

YANG Liming, WANG Yuanjun

Diffusion tensor imaging is an essential technique to study tissue brain microstructure and the distribution of white matter fiber tracts. However, affected by the diffusion-weighted signal attenuation and long echo time, diffusion tensor images suffer from serious low signal-to-noise ratio problem. Therefore, efficient denoising techniques are crucial for enhancing image quality. This paper starts with the principle of diffusion tensor imaging and the types of noise. Then it discusses the classical diffusion tensor image denoising algorithms, including algorithms based on traditional image processing and deep learning. Special emphasis is given to the status and shortcomings of diffusion tensor image denoising research. The denoising evaluation criteria and commonly used public datasets are also introduced, followed by experiments and quantitative analysis on the diffusion tensor image denoising methods mentioned in this paper. Finally, it concludes with a summary and an outlook for the field’s future research directions.

Norbert Maes, Sergey Churakov, Sergey Churakov et al.

After isolation of radioactive waste in deep geological formations, radionuclides can enter the biosphere via slow migration through engineered barriers and host rocks. The amount of radionuclides that migrate into the biosphere depends on the distance from a repository, dominant transport mechanism (diffusion vs. advection), and interaction of dissolved radionuclides with minerals present in the host rock and engineered barrier systems. Within the framework of the European Union’s Horizon 2020 EURAD project (https://www.ejp-eurad.eu/), a series of state-of-the-art reports, which form the basis of a series of papers, have been drafted. This state-of-the-art paper aims to provide non-specialists with a comprehensive overview of the current understanding of the processes contributing to the radionuclide retention and migration in clay and crystalline host rocks, in a European context. For each process, a brief theoretical background is provided, together with current methodologies used to study these processes as well as references for key data. Owing to innovative research on retention and migration and the extensive knowledge obtained over decades (in the European context), process understanding and insights are continuously improving, prompting the adaptation and refinement of conceptual descriptions regarding safety assessments. Nevertheless, there remains important research questions to be investigated in the future.

Manlin HU, Nan LI, Yiming LI et al.

In order to solve the problem that the fault current can not correctly indicate the fault section due to the connection of photovoltaic power to the distribution network, the three-sequence component of the faulty distribution network with photovoltaic power generation is analyzed, and the negative sequence component is selected as the fault characteristic quantity. A negative sequence reconstruction scheme is proposed for the asymmetric fault scenario. The MK trend detection is used to search the negative-sequence reconstruction sequence with the most obvious fault characteristics. The negative sequence reconstruction voltage amplitude is used to determine the suspicious fault section, and the fault section is finally determined by the phase direction of negative sequence reconstruction current. A distribution network model with photovoltaic power generation is established with the PSCAD/EMTDC simulation platform. The results show that the proposed method can accurately locate the fault section of the distribution network with photovoltaic power generation under different fault types and fault locations, and can provide a theoretical basis for the rapid fault location of the distribution network with photovoltaic power generation.

Nobuyuki Umetsu, Michael Quinsat, Susumu Hashimoto et al.

The motion of chiral magnetic domain walls (DWs) driven by spin-orbit torque (SOT) has been extensively studied in heavy metal/ferromagnet heterostructures with perpendicular magnetic anisotropy. This study specifically focuses on SOT-driven DWs in near Bloch-states, which we refer to as ``quasi-Bloch DWs". These quasi-Bloch DWs exhibit slower motion compared to Neel-type DWs, offering potential for achieving highly controllable DW positions. Here, we investigate the characteristics of SOT-driven motion of quasi-Bloch DWs in perpendicularly magnetized ultra-thin films consisting of W/CoFeB/MgO. For analyzing the DW motion, we employ a one-dimensional model incorporating parameters derived from experimental data obtained from our samples. Our model successfully reproduces the experimental results, which reveal variations in the direction and threshold current density of DW motion among different samples. Through theoretical analysis, we unveil that the DW remains in quasi-Bloch states during motion, with SOT serving as the primary driving force rather than spin transfer torque (STT). The direction of motion is determined not only by the sign combination of Dzyaloshinskii-Moriya interaction (DMI) and spin Hall angle but also by the strength of DMI, STT, and extrinsic DW pinning. Furthermore, we provide analytical expressions for the threshold current density required for SOT-driven quasi-Bloch DW motion. These findings provide valuable insights for the design of future DW devices with specific film structures.

Jinxiang YANG, Yonggang PENG, Tiantian CAI et al.

Edge computing effectively relieves the computing pressure of cloud platform and reduces the consumption of network transmission bandwidth, but it brings new security problems as well, the traditional authentication mechanism no longer applies to “cloud-edge-end” network architecture. We proposed a lightweight two-way authentication protocol based on cloud-edge collaboration. In view of the limited resources of massive power terminal, the protocol is only based on a Hash and XOR operation to achieve certification, so it reduces the pressure of terminal calculation and transmission bandwidth. Its security was successfully verified by AVISPA tool together with informal analysis. The analysis and simulation results show that the protocol can resist replay attack, impersonation attack and so on. In addition, the comparison with similar protocols shows that the protocol has less computation and communication overhead.

Biaojun LI, Mei LENG, Jiashui DAI et al.

Temperature cycling test is an important test method to study the thermal fatigue aging characteristics of power module press pack insulated gate bipolar transistor (PP-IGBT) devices. Therefore, taking the PP-IGBT of flexible direct converter valve power module as the research object, and combined with theoretical calculation and finite element simulation analysis, a thermal load application method for temperature cycle test is proposed, and the corresponding electrical input target parameters are obtained. A temperature cycle test platform is built to monitor the device temperature in real time, and a comprehensive comparison analysis is made on the temperature data of the junction, shell and heatsink at the measuring point of the tested power module IGBT devices. The simulation results have verified the effectiveness of the proposed method, and can provide a research approach for the PP-IGBT test of the same type.

Daobing LIU, Miaosheng BAO, Shichun Li et al.

When the voltage of the power grid is unbalanced, the DC transmission and distribution system using modular multilevel converters (MMC) as converter devices will encounter problems such as AC current asymmetry and secondary pulsation of active and reactive power. Therefore, a hybrid control strategy of passive based control (PBC) and sliding mode control (SMC) based on port controlled dissipative Hamiltonian with Dissipation (PCHD) model is proposed. A passive sliding mode variable structure controller for MMC control system under PCHD model is designed further. Through simulation, it is verified that the proposed method has better control performance than common methods such as PI control and passive control.

Wei JIA, Yuchun HUANG

For load forecasting in renewable energy microgrid, aiming at the problem that the prediction accuracy is not high because of the lack of sample data in mid- and long-term load forecasting. This paper proposes a new data expansion method. The original data sample is used as a new data sample, and the data is filtered by setting a threshold. The data sample is expanded while ensuring the accuracy of the data, and the data based on the difference operation is analyzed. The capacity expansion method can eliminate the uncertainty of load data. Considering the influencing factors such as meteorology and population, using multiple regression analysis to fit the impact of various related factors on the load, the original data load forecasting model was used as a control, and practicality and accuracy of the expansion method in this paper was verified by comparing the error between the predicted result and the actual load.

Jingman Pang, Hongjia Wang, Yufei Tang et al.

Electric manipulation of skyrmions in 2D magnetic materials has garnered significant attention due to the potential in energy-efficient spintronic devices. In this work, using first-principles calculations and Monte Carlo simulations, we report the electric-field-tunable magnetic skyrmions in MnIn2Te4 monolayer. By adjusting the magnetic parameters, including the Heisenberg exchange interaction, DMI, and MAE, through applying an electric field, the formation or annihilation of skyrmions can be achieved. Our work suggests a platform for experimental realization of the electric-field-tunable magnetic skyrmions in 2D magnets.

Obinna P. Uzoh, Suyoung Kim, Eundeok Mun

CeCd$_3$P$_3$ and CeCd$_3$As$_3$ compounds adopt the hexagonal ScAl$_3$C$_3$-type structure, where magnetic Ce ions on a triangular lattice order antiferromagnetically below $T_\text{N} \sim$0.42~K. Their crystalline electric field (CEF) level scheme has been determined by fitting magnetic susceptibility curves, magnetization isotherms, and Schottky anomalies in specific heat. The calculated results, incorporating the CEF excitation, Zeeman splitting, and molecular field, are in good agreement with the experimental data. The CEF model, with Ce$^{3+}$ ions in a trigonal symmetry, explains the strong easy-plane magnetic anisotropy that has been observed in this family of materials. A detailed examination of the CEF parameters suggests that the fourth order CEF parameter $B_{4}^{3}$ is responsible for the strong CEF induced magnetocrystalline anisotropy, with a large $ab$-plane moment and a small $c$-axis moment. The reliability of our CEF analysis is assessed by comparing the current study with earlier reports of CeCd$_{3}$As$_{3}$. For both CeCd$_{3}X_{3}$ ($X$ = P and As) compounds, less than 40 \% of $R\ln(2)$ magnetic entropy is recovered by $T_\text{N}$ and full $R\ln(2)$ entropy is achieved at the Weiss temperature $θ_{p}$. Although the observed magnetic entropy is reminiscent of delocalized 4$f$-electron magnetism with significant Kondo screening, the electrical resistivity of these compounds follows a typical metallic behavior. Measurements of thermoelectric power further validate the absence of Kondo contribution in CeCd$_{3}X_{3}$.

Huiqian Wang, Li Liang, Xiaohui Wang et al.

The modulation of the valley structure in two-dimensional valley materials is vital in the field of valleytronics. The multiferroicity provides possibility for multiple modulations of the valley, including the magnetic and electric means. Based on the first-principle calculations, we study the valley properties and associated manipulations of multiferroic Co$_2$CF$_2$ monolayers with different stacking patterns. Our calculations show that the Co$_2$CF$_2$ monolayer in the H$^{\prime}$ phase is a ferrovalley material, with sizable valley splittings. By rotating the magnetization direction, the valley splittings can be tuned for both the magnitude and sign. The electric field, driving the reversal of the electric polarization, can also change the magnitude of the valley splittings. Besides, a metastable T$^{\prime}$ phase exhibits valley splittings as well, of which the magnitude and sign can be simultaneously controlled by applied magnetic and electric fields. These findings offer a practical way for realizing highly tunable valleys by multiferroic couplings.

Lingxiao Shan, Qi Liu, Yun Ma et al.

Hybrid metal-dielectric structures, which combine the advantages of both metal and dielectric materials, support high-confined but low-loss magnetic and electric resonances under deliberate arrangements. However, their potential for enhancing magnetic emission has not been explored. Here, we study the simultaneous magnetic and electric Purcell enhancement supported by a hybrid structure consisting of a dielectric nanoring and a silver nanorod Such a structure enables low Ohmic loss and highly-confined field under the mode hybridization of magnetic resonances on nanoring and electric resonances on nanorod in the optical communication band. So, the 60-fold magnetic Purcell enhancement and 45-fold electric Purcell enhancement can be achieved simultaneously with $>95\%$ of the radiation transmitted to far field. The position of emitter has a several-ten-nanometer tolerance for sufficiently large Purcell enhancement, which brings convenience to experimental fabrications. Moreover, an array formed by this hybrid nanostructure can further enhance the magnetic Purcell factors. The findings provide a possibility to selectively excite the magnetic and electric emission in integrated photon circuits. It may also facilitate brighter magnetic emission sources and light-emitting metasurfaces in a simpler arrangement.

Alain J. Brizard

The problem of the charged-particle motion in crossed electric and magnetic fields is investigated, and the validity of the guiding-center representation is assessed in comparison with the exact particle dynamics. While the magnetic field is considered to be straight and uniform, the (perpendicular) radial electric field is nonuniform. The Hamiltonian guiding-center theory of charged-particle motion is presented for arbitrary radial electric fields, and explicit examples are provided for the case of a linear radial electric field.