Hasil untuk "Electricity and magnetism"

WANG Yuanjun

Alzheimer's disease is the most common neurodegenerative disorder among dementia, characterized by slow disease progression and complex imaging features. Traditional image-based diagnostic processes are time-consuming and vary in accuracy. To address these challenges, this study proposes a novel classification method based on hybrid attention and multi-scale information fusion (3D HAMSNet). The method leverages image data and a convolutional neural network to enhance the model's attention to the hippocampus, amygdala, and temporal lobe through the introduction of a hybrid attention mechanism. Additionally, it integrates multiscale spatial scale features of Alzheimer's disease by using a multiscale information fusion module based on dilated convolution and soft attention, enhancing early diagnosis and prediction. Finally, tested on 198 Alzheimer's patients, 200 individuals with mild cognitive impairment, and 139 healthy controls, it achieved 94.14% accuracy, 97.07% specificity, and 94.17% F1 score—represented improvements of 9.88%, 4.94%, and 10.17% over the baseline. The method outperforms existing classification methods and provides a new approach for early Alzheimer's diagnosis.

Sungjin Ahn, Jongyoung Kim, Kyungil Kwon et al.

In this letter, we propose a novel transparent boundary condition (TBC) for finite element method-based parabolic equation (PE) analysis. Conventional PE analysis uses a Hamming window, etc., adding an extra region to suppress non-physical reflected waves, which results in an increase in the amount of computation required. In this letter, a new TBC based on the matrix pencil method is proposed to suppress non-physical reflected waves. The proposed algorithm not only reduces the computational load, since it only needs to calculate up to the actual region of interest, but also shows that non-physical reflected waves at the boundary can also be effectively suppressed.

Povilas Vaitukaitis, Jiayu Rao, Kenneth Nai et al.

Abstract This paper significantly improves the previously proposed novel multiband waveguide filter implementation employing cylindrical resonators. The improved model has the advantages of a further reduced footprint using stacking shunt resonators horizontally and vertically and the ability to realise advanced filtering functions, including transmission zeros below and above the passbands. The coupling matrix synthesis with a brief example and a detailed filter design with considerations for additional coupling and in‐line and folded topologies is given. Several filter prototypes, namely third‐order quad‐band and quintuple‐band in‐line filters and a sixth‐order dual‐band folded filter in Ku‐band, were designed to validate the proposed model. Selective laser melting (SLM), a metal 3‐D printing technique where metal powder is selectively melted with a laser layer by layer, was used to fabricate a dual‐band folded filter prototype in copper to validate the proposed model since the model has a complex inner geometry. Additionally, selective laser melting has the advantage of monolithic near‐net shape fabrication, eliminating assembly, improving reliability, and reducing weight. The measured results show good agreement with the simulations.

ZHU Xiaofeng, ZHAO Zhihong, TAN Rui et al.

Investigating the moisture migration during the wood drying process can help improve wood utilization. Single-sided nuclear magnetic resonance (NMR) technology facilitates such investigation with its advantage in conducting one-dimensional measurements along different directions of wood, allowing for the detection of moisture transfer at different depths along the axial and transverse directions during the wood drying process. This research focused on Pinus sylvestris var.mongolica wood, on which a glue sealing technique was employed to ensure that the moisture only transfers along the axial or transverse axis, and the apparent transverse relaxation time (T2app) was utilized to delve into the changes of moisture content at various depths during the drying process. The results showed that at the first 2 hours of the drying process, there was a little free water near the evaporation surface of Pinus sylvestris var.mongolica wood, followed by a scarcity of free water during the drying process, and a noticeable moisture content gradient was observed near the evaporation surface. When the moisture transferred along the axial direction, the farther the moisture was away from the evaporation surface, the more uniform the moisture distribution was. When the moisture transferred along the tangential direction, the farther the moisture was away from the evaporation surface, the more obvious the moisture difference in each layer was. By single-sided NMR technology, it is possible to ascertain the moisture content of wood at various depths, thereby offering a theoretical framework for revealing the migration mechanism of water within wood.

Bin CAO, Ke SU, Shuai YUAN et al.

In the context of high penetration of renewables, it is very important for new power system dynamic analysis to establish a dynamic model that can accurately describe the portal dynamics of renewable-integrated regional power networks under the influence of complex environmental factors. Therefore a neural differential-algebraic equations-based portal dynamics learning method is proposed for renewable-integrated regional power networks. In this method, the differential-algebraic neural network is used to learn the portal dynamics model expressed in the form of neural network based on the time series measurements of the access point of the regional power networks and the environmental measurement data such as the radiation intensity and temperature. The learned model is composed of an initial state extracting block, a neural differential equation block and an algebraic equation block, and can be directly integrated into power system transient simulations to analyze the overall dynamics of power systems. The proposed method is tested through simulation in the IEEE-39 system, and the test results show that the obtained model can adapt to different environmental scenarios with acceptable accuracy, which verifies the effectiveness of the proposed method. The modelling method only needs portal time series measurements and has great application potential in the dynamic analysis of new power systems.

Li YAO, Haifeng ZHENG, Baoguo SHAN et al.

Optimization of coal procurement and inventory for power generation enterprises are of great significance for guaranteeing power supply and ensuring generation income. The requirements for safe coal inventory level have been clearly put forward by the energy administrative authority of our country. However, no existing research has ever focused on the probabilistic model and corresponding optimization strategy for the violation risk of inventory caused by the uncertainties of power generation and transportation capacity. Aiming at this problem, this paper presents an optimization coal procurement and inventory model for power generation enterprises based on data-driven chance constraints and proposes a corresponding solution method. Firstly, with consideration of the uncertainty of power generation and transportation capacity, the data-driven chance constraints for inventory are established and converted to soluble constraints of conditional value at risk (CVaR). Furthermore, based on the convexity of CVaR to decision variables, a piecewise linear approximation method for CVaR constraints is proposed. A power generation enterprise which owns 10 coal power plants is selected for case study. The optimization results show that with consideration of the chance constraints, the violation risk of power coal inventory is restricted within the allowable range; the proposed piecewise linear approximation method for CVaR constraints can make the model scalable and reduce the model’s scale with a high accuracy.

Congan XU, Hang SU, Jianwei LI et al.

This paper releases a rotated SAR ship detection dataset, named Rotated Ship Detection Dataset in SAR Images (RSDD-SAR), to address the problem that the existing rotated SAR ship detection datasets are not enough to meet the requirements of algorithm development and practical application. This dataset consists of 84 scenes of GF-3 data slices, 41 scenes of TerraSAR-X data slices, and 2 scenes of large uncropped images, including 7,000 slices and 10,263 ship instances of multi-observing modes, multi-polarization modes, and multi-resolutions. This dataset is effectively annotated by automatic annotation with manual correction. Meanwhile, experiments were conducted for several popular rotated object detection algorithms in optical remote sensing images and rotated ship detection algorithms in SAR images, and the one-stage algorithm S2ANet achieved the highest average precision of 90.06%. When using this dataset, scholars can reference the experimental results, and corresponding analysis can be used. Finally, this paper conducts generalization ability testing experiments on other datasets and large uncropped images to analyze and discuss the performance of the model trained on RSDD-SAR. The experimental results show that the model trained on RSDD-SAR has decent performance and confirms the application value of this dataset. The RSDD-SAR dataset is available at https://radars.ac.cn/web/data/getData?dataType=SDD-SAR.

Riccardo Colella, Francesco Paolo Chietera, Andrea Michel et al.

Abstract Additive manufacturing (AM) 3D‐printing technology is increasingly bringing benefits even in electromagnetics, with interesting prospects of application. Apart from the use of additive manufacturing for realising dielectric components of suitably shaped antennas, the ambitious target is, undoubtedly, the fully 3D realisation of radiofrequency and microwave circuits as well as radiating structures, including, therefore, conductive parts. In this regard, 3D‐printable filaments with interesting conductive properties are being produced. However, their rigorous conductivity characterisation is still missing, making it difficult to estimate the real behaviour of the final 3D printed electromagnetic device. To fill this gap, the conductivity of one of the most interesting conductive filaments, named Electrifi, is first experimentally evaluated in a frequency range as large as 0.72–6 GHz, accounting also for its roughness. Then it has been validated by designing, realising, and testing three fully 3D‐printed antennas. Specifically, two bow‐tie antennas, operating at 2.8 and 4 GHz, respectively, and an ultrawideband antenna, borrowed from the existing literature, operating between 1 and 7 GHz. The good agreement between simulated and measured results demonstrates the reliability of the performed electrical conductivity characterisation, even in the design of efficient radiating structures entirely realised with thermoplastic materials with copper nanoparticle additives.

Andryushin Konstantin, Pavelko Alexey, Sahoo Sushrisangita et al.

Solid solution samples of the three-component system (1 − [Formula: see text])Pb(Ti[Formula: see text]Zr[Formula: see text])O[Formula: see text]CdNb2O6 with [Formula: see text] = 0.0125–0.0500, [Formula: see text][Formula: see text] = 0.0125 were obtained by solid phase synthesis followed by sintering using conventional ceramic technology. The crystal structure, microstructure, electrophysical, and thermophysical properties of these ceramics have been studied. It is shown that all studied solid solutions can be divided into two groups (with [Formula: see text] = 0.0125 and with [Formula: see text] 0.0125), characterized by different characteristics of the change in properties with variations in external influences. This is probably due to the transition from a perovskite-type structure with a tetragonal (T) unit cell to inhomogeneous solid solutions consisting of a series of T-phases with similar cell parameters. A conclusion is made about the expediency of using the data obtained in the development of similar materials for devices based on them.

Sihang Wu, Hong Shen, Lei Qi et al.

Abstract The high current of hybrid DC circuit breaker (HCB) in the process of breaking generates strong transient magnetic field (MF), which may interfere with the normal operation of driver control units (DCUs). Therefore, the analysis for transient MF disturbance is of great significance. Due to the large space scale of HCB, with the large number of power electronic devices, the numerical calculation method has the disadvantages of large consumption of resources and slow calculation speed in solving the transient MF inside the HCB. In this study, the current generation mechanism of a 500 kV HCB is analysed, and the equivalent current path is obtained by considering the skin effect. Combined with the temporal and spatial distribution of transient current, the multi‐process transient equivalent model of transient MF calculation is established, and the model has the advantages of high precision and high speed. Then, the breaking experiment of HCB is carried out, and the transient MF near the DCU is measured. The experiment results verify the validity of the model. Furthermore, the disturbance of transient MF at the DCU of the transfer branch during breaking 25 kA current is analysed.

Y. Sano, H. Nagano

Abstract. The history of the research on the SC (sudden commencement) of magnetic storms before World War II is studied in this paper. Since geomagnetic research activities before World War II are still not yet fully known, this paper aims to reveal some historical facts related to SC investigation at that time. The first conclusion of this paper is the possible first discoverer of the simultaneity of SC at distant locations. We show that a Portuguese scientist had already pointed it out 16 years earlier than believed. The second conclusion is the role and activities of Aikitu Tanakadate as the reporter of the SC investigation committee of STME (Section of Terrestrial Magnetism and Electricity) and IATME (International Association of Terrestrial Magnetism and Electricity) in the IGGU (International Geodetic and Geophysical Union) or IUGG (International Union of Geodesy and Geophysics). Very little was known about his activities as the reporter of this committee. Our investigation at the Tanakadate Aikitu Memorial Science Museum disclosed how he acted and what he thought of SC, based on his frequent letters to and from other scientists. The third conclusion concerns SC research carried out by Japanese scientists during the period of the Second International Polar Year (1932–1933). Not only Tanakadate but also many other Japanese scientists participated in SC research during this international project. This formed a traditional basis of SC investigation in Japan, prompting a number of Japanese scientists to study SC after World War II.

Haotian Wang, Jun-Hong Guo

Quasicrystals show some excellent properties including high strength, corrosion resistance, low friction coefficient, low conductivity and low level of porosity. Due to their special structures, which are sensitive to force, electricity, magnetism, heat and optics. Quasicrystals with piezoelectric effect can be applied in surface modification of materials and reinforced composites. Thus, it is of great significance to consider the layered structures made of piezoelectric quasicrystal (PQC) composites. In engineering practice, due to manufacturing or interlaminar aging and other reasons, microcracks or cavities may appear in the material, which will lead to material interface slip or debonding. Such interface is commonly called imperfect interface. In this paper, the generalized linear spring layer model is introduced to obtain the imperfect interface propagator matrix for PQC plates, analytical solutions of static bending deformation of 1D hexagonal PQC layered plates with imperfect interface are derived under electroelastic loads. The influence of stacking sequence and imperfect interface degree of sandwich plates composed of piezoelectric materials and quasicrystal materials on the field response of two sandwich plates is analyzed. Some important results are found from the numerical analysis, which provides theoretical reference for the study of physical properties of quasicrystals, and the optimization and design of PQC composites.

Ghulam Hazrat Aimal Rasa, G. Auzerkhan

Regarding the importance of teaching linear differential equations, it should be noted that every physical and technical phenomenon, when expressed in mathematical sciences, is a differential equation. Differential equations are an essential part of contemporary comparative mathematics that covers all disciplines of physics (heat, mechanics, atoms, electricity, magnetism, light and wave), many economic topics, engineering fields, natural issues, population growth and today’s technical issues. Used cases. In this paper, the theory of third-order heterogeneous linear differential equations with boundary problems and transforming coefficients into multiple functions p(x) we will consider. In mathematics, in the field of differential equations, a boundary problem is called a differential equation with a set of additional constraints called boundary problem conditions. A solution to a boundary problem is a solution to the differential equation that also satisfies the boundary conditions. Boundary problem problems are similar to initial value problems. A boundary problem with conditions defined at the boundaries is an independent variable in the equation, while a prime value problem has all the conditions specified in the same value of the independent variable (and that value is below the range, hence the term "initial value"). A limit value is a data value that corresponds to the minimum or maximum input, internal, or output value specified for a system or component. When the boundaries of boundary values in the solution of the equation to obtain constants D1, D2, D3 to lay down Failure to receive constants is called a boundary problem. We solve this problem by considering the conditions given for that true Green expression function. Every real function of the solution of a set of linear differential equations holds, and its boundary values depend on the distances. Key words: Green Function, Boundary Problem, Private Solution, Public Solution, Wronskian Determinant.

Sharmin Jahan, Booshrat E. Sharmin, Nure Alam Chowdhury et al.

A theoretical investigation has been carried out to examine the ion-acoustic shock waves (IASHWs) in a magnetized degenerate quantum plasma system containing inertialess ultra-relativistically degenerate electrons, and inertial non-relativistic positively charged heavy and light ions. The Burgers equation is derived by employing the reductive perturbation method. It can be seen that under the consideration of non-relativistic positively charged heavy and light ions, the plasma model only supports the positive electrostatic shock structure. It is also observed that the charge state and number density of the non-relativistic heavy and light ions enhance the amplitude of IASHWs, and the steepness of the shock profile is decreased with ion kinematic viscosity. The findings of our present investigation will be helpful in understanding the nonlinear propagation of IASHWs in white dwarfs and neutron stars.

Puja Kumari, Pankaj Sarkar, Rowdra Ghatak

Abstract This paper presents a novel technique to design an ultra‐wideband bandpass filter (UWB BPF) based on fractal tree stub loaded multimode resonators. Two different topologies are opted to verify the relationships between resonant modes of the multimode resonators with different parameters of the fractal tree stub. UWB bandwidth is acquired by increasing iterations of the fractal tree without a significant effect on the filter's physical size. The proposed topologies provide design flexibility in terms of resonance and bandwidth, which are directly related to the iteration order of the fractal tree used. To verify all the features of fractal‐tree‐based UWB BPF, the proposed UWB BPF is parametrically studied using electromagnetic simulation, and a prototype is fabricated. The measured and simulated results are in close agreement. The actual size of the filters is 11.5 × 9.6 mm2. The proposed filter covers the whole band of UWB with a minimum insertion loss of 1 dB and return loss is better than 10 dB. The measured stopband extends up to 16 GHz.

M. Elhabchi, M. N. Srifi, R. Touahni

In this paper, we present a modified UWB antenna with hexagonal slotted ground plane inspired with a double combined symmetric T-shaped slots and dual rotated L-shaped strip for dual band notched characteristics. Initially, the operating frequency range is from 3GHz to 12 GHz. To eliminate the unwanted C-band (3.625-4.2GHz) and the entire uplink and downlink of X-band satellite communication systems (7.25 -8.39 GHz) frequency bands, we are investigating the conventional UWB patch antenna and loaded it with a mentioned strips and slots respectively. The performances of the antenna are optimized both by CST Microwave Studio and Ansoft HFSS. To further analyze the parametric effects of the slots and strips, the surface current distribution is presented and discussed. The antenna gain versus frequency gives an acceptable value except the notched band regions, these values are   reduced from its normal  to be  a negative in  the notched bands (3.625-4.2GHz) and (7.25 to 8.39 GHz).

ZHOU Zi-fa, CHEN Fu, ZHANG Hua-ming

Electron paramagnetic resonance (EPR) parameters (i.e., g factor and hyperfine structure constant A) of the Cu2+ centers in Cu1-xHxZr2(PO4)3 were simulated theoretically using high-order perturbation formulas for Cu2+ in rhombically elongated octahedra. The Cu-O bond-lengths of the[CuO6]10- cluster in the Cu1-xHxZr2(PO4)3 crystal were found to be R|| ≈ 0.241 nm and R⊥ ≈ 0.215 nm. The plane bond angle was τ ≈ 80.1°. Because of reduced symmetry, the ground state wave function exhibited admixtures between 2A1g(θ) and 2A1g(ε) with a mixing coefficient α≈0.995. The calculated EPR parameters showed good agreement with the experimental data.

S. Probst, G. Zhang, M. Rančić et al.

<p>We report measurements of electron-spin-echo envelope modulation (ESEEM) performed at millikelvin temperatures in a custom-built high-sensitivity spectrometer based on superconducting micro-resonators. The high quality factor and small mode volume (down to 0.2 pL) of the resonator allow us to probe a small number of spins, down to <span class="inline-formula">5×10²</span>. We measure two-pulse ESEEM on two systems: erbium ions coupled to <span class="inline-formula">¹⁸³W</span> nuclei in a natural-abundance <span class="inline-formula">CaWO₄</span> crystal and bismuth donors coupled to residual <span class="inline-formula">²⁹Si</span> nuclei in a silicon substrate that was isotopically enriched in the <span class="inline-formula">²⁸Si</span> isotope. We also measure three- and five-pulse ESEEM for the bismuth donors in silicon. Quantitative agreement is obtained for both the hyperfine coupling strength of proximal nuclei and the nuclear-spin concentration.</p>

Yinxing XIANG, Xiaojian TANG, Jikeng LIN

How to quickly generate a black-start path and system restoration scheme has always been one of the urgent problems needing to be solved in emergency response of power system. This paper develops an assistant decision-making system for black-start path generation and system restoration scheme based on 3D visualization technology. Firstly, The overall framework architecture of the system is introduced; And then, the module functions and its implementation methods of the system are further described in detail, including data base, graph platform, and algorithm library that is composed of initial path generation, path check and assessment, and system restoration; Finally, an actual power system is used to verify the effectiveness and correctness of the designed system. The results show that the designed system has a perfect integrated graph-model system formed by graphical interface, database system and algorithm library, which has the advantages of reasonable configuration, complete functions and convenient for use.

A. Scherer, S. Tischlik, S. Weickert et al.

<p>EPR distance determination in the nanometre region has become an important tool for studying the structure and interaction of macromolecules. Arbitrary waveform generators (AWGs), which have recently become commercially available for EPR spectrometers, have the potential to increase the sensitivity of the most common technique, double electron–electron resonance (DEER, also called PELDOR), as they allow the generation of broadband pulses. There are several families of broadband pulses, which are different in general pulse shape and the parameters that define them. Here, we compare the most common broadband pulses. When broadband pulses lead to a larger modulation depth, they also increase the background decay of the DEER trace. Depending on the dipolar evolution time, this can significantly increase the noise level towards the end of the form factor and limit the potential increase in the modulation-to-noise ratio (MNR). We found asymmetric hyperbolic secant (HS<span class="inline-formula"><i>{</i>1,6<i>}</i></span>) pulses to perform best for short DEER traces, leading to a MNR improvement of up to 86&thinsp;% compared to rectangular pulses. For longer traces we found symmetric hyperbolic secant (HS<span class="inline-formula"><i>{</i>1,1<i>}</i></span>) pulses to perform best; however, the increase compared to rectangular pulses goes down to 43&thinsp;%.</p>