Paraelectric Doping Simultaneously Improves the Field Frequency Adaptability and Dielectric Properties of Ferroelectric Materials:A Phase-Field Study

Recent years,the polarization response of ferroelectrics has been entirely studied.However,it is found that the polarization may disappear gradually with the continually applied of electric field.In this paper,taking K0.48Na0.52NbO3(KNN)as an example,it was demonstrated that the residual polarization began to decrease when the electric field frequency increased to a certain extent using a phase-field methods.The results showed that the content of out-of-plane domains increased first and then decreased with the increase of applied electric field frequency,the maximum polarization disappeared at high frequencies,and the hysteresis loop became elliptical.In order to further study the abnormal changes of hysteresis loops of ferroelectrics under high electric field frequency,we analyzed the hysteresis loop and dielectric response of solid solution 0.1SrTiO_(3)-0.9K_(0.48)Na_(0.52)NbO_(3).It was found that the doped hysteresis loop maintained its shape at higher frequency and the dielectric constant increased.This kind of doping has a higher field frequency adaptability,which has a key guiding role in improving the dielectric properties of ferroelectric thin films and expanding the frequency application range of ferroelectric nano memory。

Effects of harmonic electric field frequency on electromagnetic and flow fields of Ti-Al melt in a rectangular mold based on numerical simulation

A model was established based on Maxwell's equations and Navier-Stokes' equations to numerically simulate the electromagnetic field and flow field in a rectangular mold with sectional aspect ratio of 5:1. The FEM (Finite Element Method) and APDL (ANSYS Parametric Design Language) were employed for the model to execute the modeling, meshing, load applying and solving. The Ti-Al alloy melt was selected to illustrate and validate the effects of the harmonic field frequency on the distribution of the physical fields in the mold. The simulated results demonstrate that with an increasing frequency the electric current forms an ellipsoid cavity where it becomes much weaker, and that the melt flows more intensely with low frequency (less than 5 kHz) than with high frequency (more than 5 kHz). The melt is pinched from the central part in the mold to bipolar parts in which it forms two vortexes in each side. The maximum value of fluid velocity exists near the bipolar zone.

DIRECT SOLUTION BY 2-D AND 3-D FINITE ELEMENT METHOD ON FORWARD PROBLEM OF LOW FREQUENCY CURRENT FIELDS IN INHOMOGENEOUS MEDIA

The paper adopts finite element method to analyze the forward problem of low-frequency current fields in inhomogeneous media. Firstly, the direct solution of 2-D and 3-D scalar potential is given. Secondly, the technique of covering finite elements for problems with movement has been presented; namely, when the place of testing point moved, the meshing data will be produced automatically to avoid re-meshing and distortion of the mesh. Thirdly the free and prescribed potential method is used to make the finite element coefficient matrices. Then this paper provides the result of a validity test obtained by simulating the laterolog-3 logging, compared with the numerical model-matching method. Finally, the MLL response is calculated.

Frequency-time Domain Shielding Effectiveness of Materials and Their Strong Electromagnetic Field Test

To describe the shielding ability of materials accurately and comprehensively,the frequency-domain and time-domain shielding effectiveness(SE) of material is investigated.The relevance between them was analyzed based on the minimum phase method,and the time-domain SE can be derived from frequency-domain SE.The SE of an energy selective surface(ESS) made of a novel material is investigated,and the relationship between SE and radiation field intensity are analyzed.The results show that not only material,but also the intensity of radiation electric field shows influence on SE in its frequency; for some materials,the dependence of SE on radiation electric field intensity needs to be considered.Therefore,it is necessary to research on the SE of shielding material in high-intensity electromagnetic environment.

Finite Element Method for Transient Electric Field by Using Indirect Laplace Transform with High Accuracy

This paper focuses on the finite element method in the complex frequency domain(CFD-FEM)for the transient electric field.First,the initial value and boundary value problem of the transient electric field under the electroquasistatic field in the complex frequency domain is given.In addition,the finite element equation and the constrained electric field equation on the boundary are derived.Secondly,the indirect algorithm of the numerical inverse Laplace transform is introduced.Based on it,the calculation procedures of the CFD-FEM are illustrated in detail.Thirdly,the step response,zero-state response under the positive periodic square waveform(PPSW)voltage,and the zero-input response by the CFD-FEM with direct algorithm and indirect algorithm are compared.Finally,the reason for the numerical oscillations of the zero-state response under the PPSW voltage is analyzed,and the method to reduce oscillations is proposed.The results show that the numerical accuracy of the indirect algorithm of the CFD-FEM is more than an order of magnitude higher than that of the direct algorithm when calculating the step response of the transient electric field.The proposed method can significantly reduce the numerical oscillations of the zero-state response under the PPSW voltage.The proposed method is helpful for the calculation of the transient electric field,especially in the case of frequency-dependent parameters.

Analysis of Mechanically Tunable Frequency Selective Surfaces

The frequency selective surface (FSS) has been widely applied by means of its spatial frequency-filter characteristic, but it is always designed and used as a device with fixed frequency response. In order to tune the resonant frequency and switch the frequency channel, a scheme of mechanically tunable FSS is theoretically analyzed by using the method of Floquet's vector modes expansion and fields matching. A double-layer tunable FSS with dipole element can perform a dynamic range of resonant frequency covering whole X-band.

The Background Variation of Natural Source ELF and Its EM Abnormal Phenomena in Yunnan Earthquakes

In order to add earthquake monitoring methods and develop new method research,the ELF Network for Earthquake Monitoring selected 30 stations in the Capital Circle and the Sichuan-Yunnan region. Finding electromagnetic field background variation is the basis of distinguishing the seismic electromagnetic anomalies. This paper introduces the data acquisition and selection of the Shexian,Anqiu,Lijiang and Dali stations which have recorded for longer time with better data and are located on the similar latitude. Then we use the natural source electromagnetic field's auto-power spectrum to express the intensity of the electromagnetic field. By using power spectral data of many frequencies in the observation frequency band,after the data pre-processing and sliding average noising,the background variation of extremely low frequency stations and the range ability were acquired.Taking the Baoshan M5. 1 earthquake on October 30,2015 and Dali M5. 0 earthquake on May 18,2016 as examples,the authors analyzed the earthquake electromagnetic anomaly characteristic of ELF stations around the earthquakes.

肿瘤治疗电场在肿瘤治疗中的应用和机制研究进展

[背景]肿瘤治疗领域缺乏高效、安全的非侵入式治疗方法.近年来,肿瘤治疗电场(tumor treating fields,TTFields)作为一种新兴的非侵入性物理治疗技术,通过释放中频、低强度的交变电场有效抑制肿瘤生长,引发的副作用较小.[进展]目前TTFields已被广泛应用于各类肿瘤治疗的临床研究中,包括脑胶质瘤、间皮质瘤、非小细胞肺癌、胰腺癌、卵巢癌、肝癌及胃癌等.TTFields通过向生物分子施加生物物理力,扰乱肿瘤细胞的生物学功能从而抑制其生长,但具体分子机制尚不明确.为研究TTFields在肿瘤治疗中的分子机制,研究人员通过设计和搭建不同电极和交变电场发生平台,在体外研究TTFields对肿瘤细胞的作用机制.研究发现TTFields干扰细胞分裂、DNA修复、自噬、细胞迁移和细胞膜通透性等生物学过程,也影响血脑屏障、血管生成和肿瘤免疫等肿瘤微环境.[展望]本文回顾了近年来TTFields在肿瘤治疗中的应用、用于体外研究的电极设计和电场发生平台,及其潜在的抗肿瘤机制.然而,TTFields抑制肿瘤生长的分子机制仍需深入研究,评估其对能够自我更新的非肿瘤细胞和终端分化细胞的影响,以减少可能的副作用.这些研究将有助于提升TTFields的治疗潜力,为更多恶性肿瘤的治疗开辟新的可能性.

基于标准场法的低频电场计量技术探讨

为了实现低频电场测量仪的校准,探讨了基于标准场法的低频电场计量技术。描述了低频电场测量仪的结构和工作原理,分析了应用平行板产生可计算标准电场的方法,研究构建了校准系统。应用该系统进行了校准测量实验,分析了测量误差来源,评估了测量结果的不确定度。将实验结果与应用横电磁波室法的测量结果作了比较,数据表明该校准系统的测量结果合理,满足低频电场测量仪的校准要求。

天然电场选频法在高压线干扰环境下的浅层地下水勘探

在工程地球物理的实践应用中,人文环境因素对勘探的影响常常是无法避免的。主要探讨天然电场选频法(frequency selectionmethod,FSM)在高压输电线附近开展地下水勘探的应用效果。首先,简单介绍静态效应的起因,并通过对天然电磁法二维有限元正演模拟,在以往研究成果的基础上进一步说明当近地表存在相对低阻异常体时,地表沿测线方向的水平电场分量会出现明显的静态效应;其次,将FSM应用于2处地下水勘探,验证FSM在高压输电线干扰下的应用效果,并利用实测结果说明FSM的异常成因主要是静态效应所致。根据理论模拟和实践可知,FSM实测的剖面曲线及拟断面图会出现明显的静态效应现象,且与理论模拟结果类似。同时,在高压线干扰环境下,只要测线方向与输电线方向平行,同样可取得成功的应用效果。这为今后类似环境下的应用提供了一种可供选择的物探方法。

一种暴时电离层f_oF_2的经验预报方法

利用地磁指数Dst和AE以及电离层临界频率f0F2，通过分析磁扰期问成分扰动带的赤道向传播以及低纬穿透电场引起的等离子体漂移对电离层的影响，同时考虑地方时效应，提出一种提前1小时预报暴时电离层f0Fz的经验方法，并对2004～2005年10次磁暴期间的预报结果进行检验。结果表明，该方法能较好地预测中低纬电离层暴的演化，甚至能捕捉部分正负相交替出现的扰动，但对部分重复出现的正扰动尚有待改进。方法在磁暴事件中和暴目的平均预报误差低于国际参考电离层（IRI）中用于暴时修正的STORM模型，因而更具有实用性。

基于FLAC3D的石灰岩矿区岩溶塌陷数值模拟研究

矿区为露天凹陷式开采的石灰岩建材矿山,随着矿山开采以及地下水抽排,导致矿坑周边岩溶塌陷大量产生,严重影响矿山安全生产和周边群众生产生活。利用FLAC3D技术、天然电场选频法勘探和地质综合分析掌握岩溶塌陷发生机理和分布规律,研究结果表明矿坑东侧、北侧和南侧断裂构造发育;矿山生产抽排地下水以及采矿爆破引起真空吸蚀、流水潜蚀导致矿坑周边岩溶塌陷;基于FLAC3D技术矿区岩溶塌陷数值模拟分析,数值模拟结果与地质分析、物探结论和塌陷现状基本一致。研究结果为后期岩溶塌陷的防治提供了科学依据。

自然电场法在冀北围场县浅覆盖区某萤石矿勘查中的应用

围场北部地区萤石矿床发育,多为热液充填型萤石矿床,萤石矿的产出与断层密切相关。研究区被黄土和冲洪积砂砾层覆盖,通过常规地质手段很难到达寻找矿体的目的。而自然电场法相对其他地球物理方法具有施工便捷、成本低、速度快的特征,对于寻找浅覆盖区的含水断层具有良好的效果。本次工作经过综合研究研究区的地质和矿体特征,首次通过自然电场圈出了含水构造的范围。在重点剖面布设钻孔进行验证,见到了厚度较大的萤石矿体,通过寻找含水断层间接达到了寻找萤石矿的目的。这为冀北其他此类型矿山找矿提供启示和借鉴经验。

变频电机定子绕组电场分布的仿真研究

本文基于COMSOL Multiphysics建立了一台变频电机定子绕组绝缘结构的仿真模型,分别计算了变频运行时匝间绝缘和对地绝缘所承受的电场强度,考察了浸渍过程中产生的不同位置、大小的气泡中的最大电场强度,以及半导体高阻带对于电场分布的影响。仿真结果表明本电机现行绝缘结构足以承受变频运行时的应力,且有一定裕量。

基于有限元法和模拟电荷法的高压输电线路工频电场研究

为更好地研究高压输电线路工频电场效应在不同气象条件下的变化规律,运用有限元法和模拟电荷法,结合高压输电线下工频电场相关理论知识,在高压输电线路下,分析车辆对人体的电击效应。首先,对人体的暂态电击电流峰值、暂态放电能量和稳态电击电流进行精确计算。其次,应用有限元法,仿真和分析小型车对人体所产生的暂态电击电流峰值以及暂态放电能量,并比较最终仿真结果。结果表明:理论计算值与仿真分析值之间存在10%左右的误差,当人所处的电场强度为5~10kV/m,且接触小型车时,由于该场强没有超出人体的疼痛阈值,人体仅仅出现触电感觉,不会危及人体生命安全。高压输电线路工频电场场强低于人体疼痛阈值,安全可靠,并不会对人体造成生命危险。该研究成果能够为相关人员提供有益的借鉴和参考。

基于有限元法的串补站电场分布特性研究

串补工程所涉设备繁多,在布置上与常规站有明显差别,其对电站电磁环境有较大影响。采用三维有限元分析计算方法,结合国外某400 kV串补工程,建立三相完整模型,对串补站近地工频电场分布及其影响因素展开研究。通过模型的对比分析表明:设计尺寸下的串补站近地电场分布满足限值要求,单一因素的变化仅对相关设备邻近区域的电场分布有显著影响;在一定范围内,平台及围栏越高,线路距离越近,近地电场分布所受影响越趋积极。

Vibration of two-dimensional hexagonal boron nitride

The dynamic behavior of two-dimensional nanostructures is important to the future application of nano devices. The vibrational behaviors of single-layered hexagonal boron nitride(h-BN) are studied by molecular dynamics simulation and continuum plate model. The bending stiffness and Poisson’s ratios of h-BN along zigzag direction and armchair direction are calculated. H-BN is softer compared with graphene. The continuum plate model can predict the vibration of h-BN with four edge-clamped boundary conditions well. The electric fields in different directions have obvious influence on the vibration of h-BN. The natural frequency of h-BN changes linearly with the electric field intensity along the polarization direction. The natural frequency of h-BN decreases with the increase of electric field intensity along both positive and negative nonpolarization direction. While the natural frequency of h-BN increases with the increase of electric field intensity along both positive and negative transverse electric field.

粒子群优化模拟电荷法在HGIS工频电场计算中的应用

近年来,复合型气体绝缘组合开关设备(HGIS)以其造价适中、占地面积小、运行安全可靠等优点,在我国超高压变电站的建设中得到越来越多的应用。研究分析HGIS配电装置区的工频电场分布规律,对智能变电站的设计与建设、电磁环境评估以及消除民众对电磁辐射问题的不必要担忧等方面具有重要意义。鉴于传统模拟电荷法(CSM)布点和校验环节过于繁琐,难以应对复杂场景。提出将粒子群优化算法(PSO)和传统模拟电荷法结合,形成粒子群优化模拟电荷法(PSO-CSM)。并将其应用到500 kV HGIS配电装置区工频电场的计算中,研究分析配电装置区内各主要设备对工频电场的影响以及整个配电装置区工频电场的分布状况,并提出变电站工频电场防护的相关建议和改进措施。

热环境下热电材料圆板的横向自由振动特性

为获得热环境作用下热电材料圆板的横向自由振动特性,基于经典板理论和热电材料固有性质,建立热环境下热电材料圆板轴对称自由振动的控制微分方程.采用微分变换法(DTM)对无量纲控制微分方程及边界条件进行变换,分别得到周边简支和固支约束条件下热电材料圆板横向自由振动的无量纲固有频率.退化后与各向同性圆板自由振动的固有频率进行对比,验证研究方法行之有效.讨论不同时刻、不同输入热流和不同外加电流密度对热电圆板瞬态温度场的影响,以及上表面温度和外加电流密度对无量纲固有频率的影响.结果表明:热电材料圆板的无量纲固有频率随上表面温度的升高而减小,随外加电流密度的减小而增大,边界约束条件越强,固有频率越大.

自然正交函数方法在强震预测中应用

1研究背景许多著名学者一致认为自然正交函数方法是预测、评估和检验大规模数据中短期和长期变化的最先进工具(Dawson,2016;Chao,2019;Neha et al,2021)。然而自然正交函数方法最先应用在大气、气候和气象预测上(马开玉等,1993),近年来该方法逐渐应用在强震预测研究中。在中国,采用正交函数方法计算强震前的能量场(杨明芝,2004)、应变场(杨明芝,2017;罗国富,2023)和频次场(罗国富,2023),提取场的时间和空间异常信息,分析与强震的关系。在日本、印度以及欧美国家,采用经验正交函数方法计算强震前后的变形场(Chang,2011;Chao,2019;Neha et al,2021),分析强震的同震变形,给出三维变形的运动方向。