基于RF-RFE算法的地铁车站洪涝灾害预测研究

地铁车站形式以地下段为主,进入雨期时受到洪涝灾害的威胁,易发生雨水倒灌现象,严重影响居民出行和地铁安全运营。为进一步提高地铁车站洪涝灾害预测的效果,提出基于RF-RFE和DNN神经网络的地铁车站洪涝灾害预测方法。首先,通过收集并分析已发生地铁车站洪涝灾害的案例,采用文献综述结合专家访谈的方法,构建地铁车站洪涝灾害初始变量集;然后,利用随机森林—递归特征消除(RF-RFE)算法,计算初始变量重要性并完成变量分类正确率排序,从初始变量集中筛选出重要变量;最后,建立DNN神经网络预测模型,并以筛选出的重要变量作为输入样本,训练DNN神经网络,完成对地铁车站洪涝灾害的预测。研究结果表明:(1)变量选择可提高预测模型精度,与初始变量集的DNN神经网络预测模型相比,数据筛选后的DNN神经网络预测模型准确率提高了4.36%;(2)RF-RFE和DNN神经网络算法结合具有良好的效果,预测模型准确率为88.1%,F1分数为0.9。

Robust and Tunable Ferroelectricity in Ba/Co Codoped (K_(0.5)Na_(0.5))NbO_(3) Ceramics

The 0.98(K_(0.5)Na_(0.5))NbO_(3)-0.02Ba(Nb_(0.5)Co_(0.5))O_(3-δ) ceramics with doped Ba^(2+) and Co^(2+) ions are fabricated,and the impacts of the thermal process are studied.Compared with the rapidly cooled (RC) sample,the slowly cooled (SC) sample possesses superior dielectric and ferroelectric properties,and an 11 K higher ferroelectricparaelectric phase transition temperature,which can be attributed to the structural characteristics such as the grain size and the degree of anisotropy.Heat treatment can reversibly modulate the content of the oxygen vacancies,and in turn the ferroelectric hysteresis loops of the samples.Finally,robust and tunable ferroelectric property is achieved in SC samples with good structural integrity.

Structural and Ferroelectric Transition in Few-Layer HfO_(2) Films by First Principles Calculations

The discovery of ferroelectricity in HfO_(2)-based materials with high dielectric constant has inspired tremendous research interest for next-generation electronic devices.Importantly,films structure and strain are key factors in exploration of ferroelectricity in fluorite-type oxide HfO_(2) films.Here we investigate the structures and straininduced ferroelectric transition in different phases of few-layer HfO_(2) films(layer number𝑁=1–5).It is found that HfO_(2) films for all phases are more stable with increasing films thickness.Among them,the Pmn2_(1)(110)-oriented film is most stable,and the films of𝑁=4,5 occur with a𝑃21 ferroelectric transition under tensile strain,resulting in polarization about 11.8μC/cm^(2) along in-plane𝑎-axis.The ferroelectric transition is caused by the strain,which induces the displacement of Hf and O atoms on the surface to non-centrosymmetric positions away from the original paraelectric positions,accompanied by the change of surface Hf–O bond lengths.More importantly,three new stable HfO_(2)2D structures are discovered,together with analyses of computed electronic structures,mechanical,and dielectric properties.This work provides guidance for theoretical and experimental study of the new structures and strain-tuned ferroelectricity in freestanding HfO_(2) films.

Hole-Doped Nonvolatile and Electrically Controllable Magnetism in van der Waals Ferroelectric Heterostructures

Electrical control of magnetism in van der Waals semiconductors is a promising step towards development of two-dimensional spintronic devices with ultralow power consumption for processing and storing information.Here, we propose a design for two-dimensional van der Waals heterostructures(vdWHs) that can host ferroelectricity and ferromagnetism simultaneously under hole doping. By contacting an In Se monolayer and forming an InSe/In_(2)Se_(3) vd WH, the switchable built-in electric field from the reversible out-of-plane polarization enables robust control of the band alignment. Furthermore, switching between the two ferroelectric states(P_↑ and P_↓)of hole-doped In_(2)Se_(3) with an external electric field can interchange the ON and OFF states of the nonvolatile magnetism. More interestingly, doping concentration and strain can effectively tune the magnetic moment and polarization energy. Therefore, this provides a platform for realizing multiferroics in ferroelectric heterostructures,showing great potential for use in nonvolatile memories and ferroelectric field-effect transistors.

BaTiO_(3)/p-GaN/Au self-driven UV photodetector with bipolar photocurrent controlled by ferroelectric polarization

Ferroelectric materials are promising candidates for ultraviolet photodetectors due to their ferroelectric effect.In this work,a BaTiO_(3)/p-GaN/Au hybrid heterojunction-Schottky self-driven ultraviolet photodetector was fabricated with excellent bipolar photoresponse property.At 0 V bias,the direction of the photocurrent can be switched by flipping the depolarization field of BaTiO_(3),which allows the performance of photodetectors to be controlled by the ferroelectric effect.Meanwhile,a relatively large responsivity and a fast response speed can be also observed.In particular,when the depolarization field of BaTiO_(3) is in the same direction of the built-in electric field of the Au/p-GaN Schottky junction(up polarized state),the photodetector exhibits a high responsivity of 18 mA/W at 360 nm,and a fast response speed of<40 ms at 0 V.These findings pave a new way for the preparation of high-performance photodetectors with bipolar photocurrents.

New‑Generation Ferroelectric AlScN Materials

Ferroelectrics have great potential in the field of nonvolatile memory due to programmable polarization states by external electric field in nonvolatile manner.However,complementary metal oxide semiconductor compatibility and uniformity of ferroelectric performance after size scaling have always been two thorny issues hindering practical application of ferroelectric memory devices.The emerging ferroelectricity of wurtzite structure nitride offers opportunities to circumvent the dilemma.This review covers the mechanism of ferroelectricity and domain dynamics in ferroelectric AlScN films.The performance optimization of AlScN films grown by different techniques is summarized and their applications for memories and emerging in-memory computing are illustrated.Finally,the challenges and perspectives regarding the commercial avenue of ferroelectric AlScN are discussed.

Ultra‑Stable Sodium‑Ion Battery Enabled by All‑Solid‑State Ferroelectric‑Engineered Composite Electrolytes

Symmetric Na-ion cells using the NASICON-structured electrodes could simplify the manufacturing process,reduce the cost,facilitate the recycling post-process,and thus attractive in the field of large-scale stationary energy storage.However,the long-term cycling performance of such batteries is usually poor.This investigation reveals the unavoidable side reactions between the NASICON-type Na_(3)V_(2)(PO_(4))_(3)(NVP)anode and the commercial liquid electrolyte,leading to serious capacity fading in the symmetric NVP//NVP cells.To resolve this issue,an all-solid-state composite electrolyte is used to replace the liquid electrolyte so that to overcome the side reaction and achieve high anode/electrolyte interfacial stability.The ferroelectric engineering could further improve the interfacial ion conduction,effectively reducing the electrode/electrolyte interfacial resistances.The NVP//NVP cell using the ferroelectric-engineered composite electrolyte can achieve a capacity retention of 86.4%after 650 cycles.Furthermore,the electrolyte can also be used to match the Prussianblue cathode NaxFeyFe(CN)_(6−z)·nH_(2)O(NFFCN).Outstanding long-term cycling stability has been obtained in the all-solid-state NVP//NFFCN cell over 9000 cycles at a current density of 500 mA g^(-1),with a fading rate as low as 0.005%per cycle.

Enhanced ferroelectric and improved leakage of BFO-based thin films through increasing entropy strategy

BiFeO_(3)(BFO)has received considerable attention as a lead-free ferroelectric film due to its large theoretical remnant polariza-tion.However,BFO suffers from a large leakage current,resulting in poor ferroelectric properties.Herein,the sol-gel method was used to deposit a series of BFO-based thin films on fluorine-doped tin oxide substrates,and the effects of the substitution of the elements Co,Cu,Mn(B-site)and Sm,Eu,La(A-site)on the crystal structure,ferroelectricity,and leakage current of the BFO-based thin films were invest-igated.Results confirmed that lattice distortion by X-ray diffraction can be attributed to the substitution of individual elements in the BFO-based films.Sm and Eu substitutions contribute to the lattice distortion in a pseudo-cubic structure,while La is biased toward pseudo-tet-ragonal.Piezoelectric force microscopy confirmed that reversible switching of ferroelectric domains by nearly 180°can be realized through the prepared films.The ferroelectric hysteresis loops showed that the order for the polarization contribution is as follows:Cu>Co>Mn(B-site),Sm>La>Eu(A-site).The current density voltage curves indicated that the order for leakage contribution is as follows:Mn<Cu<Co(B-site),La<Eu<Sm(A-site).Scanning electron microscopy showed that the introduction of Cu elements facilitates the formation of dense grains,and the grain size distribution statistics proved that La element promotes the reduction of grain size,leading to the increase of grain boundaries and the reduction of leakage.Finally,a Bi_(0.985)Sm_(0.045)La_(0.03)Fe_(0.96)Co_(0.02)Cu_(0.02)O_(3)(SmLa-CoCu)thin film with a qualitative leap in the remnant polarization from 25.5(Bi_(0.985)Sm_(0.075)FeO_(3))to 98.8µC/cm^(2)(SmLa-CoCu)was prepared through the syner-gistic action of Sm,La,Co,and Cu elements.The leakage current is also drastically reduced from 160 to 8.4 mA/cm^(2)at a field strength of 150 kV/cm.Thus,based on the increasing entropy strategy of chemical engineering,this study focuses on enhancing ferroelectricity and decreasing leakage current,providing a promising path for the advancement of ferroelectric devices.

Reliable ferroelectricity down to cryogenic temperature in wakeup free Hf_(0.5)Zr_(0.5)O_(2)thin films by thermal atomic layer deposition

The performance and reliability of ferroelectric thin films at temperatures around a few Kelvin are critical for their application in cryo-electronics.In this work,TiN/Hf_(0.5)Zr_(0.5)O_(2)/TiN capacitors that are free from the wake-up effect are investigated systematically from room temperature(300 K)to cryogenic temperature(30 K).We observe a consistent decrease in permittivity(εr)and a progressive increase in coercive electric field(Ec)as temperatures decrease.Our investigation reveals exceptional stability in the double remnant polarization(2P_(r))of our ferroelectric thin films across a wide temperature range.Specifically,at 30 K,a 2P_(r)of 36μC/cm^(2)under an applied electric field of 3.0 MV/cm is achieved.Moreover,we observed a reduced fatigue effect at 30 K in comparison to 300 K.The stable ferroelectric properties and endurance characteristics demonstrate the feasibility of utilizing HfO_(2)based ferroelectric thin films for cryo-electronics applications.

Enhancing BiVO_(4)photoanode performance by insertion of an epitaxial BiFeO_(3)ferroelectric layer

BiVO_(4)(BVO)is a promising material as the photoanode for use in photoelectrochemical applications.However,the high charge recombination and slow charge transfer of the BVO have been obstacles to achieving satisfactory photoelectrochemical performance.To address this,various modifications have been attempted,including the use of ferroelectric materials.Ferroelectric materials can form a permanent polarization within the layer,enhancing the separation and transport of photo-excited electron-hole pairs.In this study,we propose a novel approach by depositing an epitaxial BiFeO_(3)(BFO)thin film underneath the BVO thin film(BVO/BFO)to harness the ferroelectric property of BFO.The self-polarization of the inserted BFO thin film simultaneously functions as a buffer layer to enhance charge transport and a hole-blocking layer to reduce charge recombination.As a result,the BVO/BFO photoanodes showed more than 3.5 times higher photocurrent density(0.65 mA cm^(-2))at 1.23 V_(RHE)under the illumination compared to the bare BVO photoanodes(0.18 m A cm^(-2)),which is consistent with the increase of the applied bias photon-to-current conversion efficiencies(ABPE)and the result of electrochemical impedance spectroscopy(EIS)analysis.These results can be attributed to the self-polarization exhibited by the inserted BFO thin film,which promoted the charge separation and transfer efficiency of the BVO photoanodes.

Structure,ferroelectric,and enhanced fatigue properties of sol–gel-processed new Bi-based perovskite thin films of Bi(Cu_(1/2)Ti_(1/2))O_(3)–PbTiO_(3)

Bi-based perovskite ferroelectric thin films have wide applications in electronic devices due to their excellent ferroelectric properties.New Bi-based perovskite thin films Bi(Cu_(1/2)Ti_(1/2))O_(3)–PbTiO_(3)(BCT–PT) are deposited on Pt(111)/Ti/SiO_(2)/Si substrates in the present study by the traditional sol–gel method.Their structures and related ferroelectric and fatigue characteristics are studied in-depth.The BCT–PT thin films exhibit good crystallization within the phase-pure perovskite structure,besides,they have a predominant(100) orientation together with a dense and homogeneous microstructure.The remnant polarization(2P_(r)) values at 30 μC/cm^(2) and 16 μC/cm^(2) are observed in 0.1BCT–0.9PT and 0.2BCT–0.8PT thin films,respectively.More intriguingly,although the polarization values are not so high,0.2BCT–0.8PT thin films show outstanding polarization fatigue properties,with a high switchable polarization of 93.6% of the starting values after 10^(8) cycles,indicating promising applications in ferroelectric memories.

Optimal parameter space for stabilizing the ferroelectric phase of Hf_(0.5)Zr_(0.5)O_(2) thin films under strain and electric fields

Hafnia-based ferroelectric materials, like Hf_(0.5)Zr_(0.5)O_(2)(HZO), have received tremendous attention owing to their potentials for building ultra-thin ferroelectric devices. The orthorhombic(O)-phase of HZO is ferroelectric but metastable in its bulk form under ambient conditions, which poses a considerable challenge to maintaining the operation performance of HZO-based ferroelectric devices. Here, we theoretically addressed this issue that provides parameter spaces for stabilizing the O-phase of HZO thin-films under various conditions. Three mechanisms were found to be capable of lowering the relative energy of the O-phase, namely, more significant surface-bulk portion of(111) surfaces, compressive c-axis strain,and positive electric fields. Considering these mechanisms, we plotted two ternary phase diagrams for HZO thin-films where the strain was applied along the in-plane uniaxial and biaxial, respectively. These diagrams indicate the O-phase could be stabilized by solely shrinking the film-thickness below 12.26 nm, ascribed to its lower surface energies. All these results shed considerable light on designing more robust and higher-performance ferroelectric devices.

Single-atom catalysts based on polarization switching of ferroelectric In_(2)Se_(3)for N2 reduction

The polarization switching plays a crucial role in controlling the final products in the catalytic pro-cess.The effect of polarization orientation on nitrogen reduction was investigated by anchoring transition metal atoms to form active centers on ferroelectric material In_(2)Se_(3).During the polariza-tion switching process,the difference in surface electrostatic potential leads to a redistribution of electronic states.This affects the interaction strength between the adsorbed small molecules and the catalyst substrate,thereby altering the reaction barrier.In addition,the surface states must be considered to prevent the adsorption of other small molecules(such as*O,*OH,and*H).Further-more,the V@↓-In_(2)Se_(3)possesses excellent catalytic properties,high electrochemical and thermody-namic stability,which facilitates the catalytic process.Machine learning also helps us further ex-plore the underlying mechanisms.The systematic investigation provides novel insights into the design and application of two-dimensional switchable ferroelectric catalysts for various chemical processes.

退火对PI/TiO_(2)/Pt/P(VDF-TrFE)/Pt柔性复合膜的铁电性的影响

本文采用溶胶凝胶法制备了PI/TiO_(2)/Pt/P(VDF-TrFE)/Pt柔性复合膜,研究了退火温度对复合膜中β相含量的影响。SEM电镜扫描结果显示,复合膜为截面清晰、结构致密性好、透光性强的二维结构。XRD衍射结果显示,在一定范围内,提高退火温度有助于α晶群转变为β晶群,130℃下β相含量达到最高,超过阈值温度后,结晶过程受到破坏,β相晶群含量明显下降。铁电测试结果显示130℃下,剩余极化强度最高为8.76μC·cm-2;温度继续升高会使铁电极化强度有明显下降,这可能与温度过高导致缺陷增多有关。

基于RFE-BXGBoost的轴承套圈沟道表面缺陷识别方法

轴承套圈是轴承部件的重要组成部分,其表面缺陷影响轴承的服役期限。为了解决轴承沟道表面缺陷难以被准确识别的问题,提出了一种基于特征递归消除的贝叶斯极度梯度提升树(RFE-BXGBoost)的轴承套圈沟道表面缺陷识别模型(方法)。首先,基于特征衍生的思想,对轴承沟道的时域、频域等特征进行了提取,使用了极度梯度提升树(XGBoost)作为基于特征递归消除(RFE)的基学习器,对影响轴承沟道表面缺陷最佳特征子集进行了选择,并过滤了冗余特征;然后,利用基于贝叶斯优化的XGBoost模型组成弱分类器,为了降低模型预测结果的方差,使用有放回随机抽样法,对基分类器进行了选取;最后,根据抽样结果,利用投票法获得了最终的表面缺陷识别结果,并使用轴承套圈沟道实测数据集进行了模型预测性能的测试。实验结果表明:基于RFE-BXGBoost的表面缺陷识别模型的识别准确率为0.90,F1-score为0.879,优于仅使用自适应提升法(Adaboost)、随机森林、梯度提升树的表面缺陷识别结果。研究结果表明:该表面缺陷识别模型对复杂零部件和系统的表面缺陷识别有一定的效果。

STUDY ON FRACTURE BEHAVIOR OF FERROELECTRIC CERAMICS UNDER COMBINED ELECTROMECHANICAL LOADING BY USING A MOIR(?) INTERFEROMETRY TECHNIQUE

This paper discusses an in situ observation of fracture behavior around a crack tip in ferroelectric ceramics under combined electromechanical loading by use of a moiré interferometry technique.The deformation field induced by the electric field and the stress concentration near the crack tip in three-points bending experiments was measured.By analysis of the moiré images it is found that under a constant mechanical load,the electric field almost has no effect on the crack extension in the case that the directions of the poling,electric field and crack extension are perpendicular to each other.When the poling direction is parallel to the crack extension direction and perpendicular to the electric field,the strain decreases faster than that calculated by FEM with and without electrical loading as one goes away from the crack tip.In addition,as the electric field intensity increases,the strain near the crack tip increases,and the strain concentration becomes more significant.

EFFECT OF CRYSTALLINITY ON POLARIZATION FATIGUE OF FERROELECTRIC P(VDF-TrFE)COPOLYMER FILMS

The dependence of polarization fatigue on crystallinity of vinylidene fluoride and trifluoroethylene copolymer films was studied.Experimental data indicated that the higher the crystallinity of the film was,the slower the fatigue rate of the film became.A possible explanation was put forward,and it was regarded that the space charges,trapped at the boundaries of crystallites and/or captured by the defects lying both in amorphous and crystalline phases,should make the major contribution to polarization fatig...

Low-Programmable-Voltage Nonvolatile Memory Devices Based on Omega-shaped Gate Organic Ferroelectric P(VDF-TrFE) Field Effect Transistors Using p-type Silicon Nanowire Channels

A facile approach was demonstrated for fabricating high-performance nonvolatile memory devices based on ferroelectric-gate field effect transistors using a p-type Si nanowire coated with omega-shaped gate organic ferroelectric poly(vinylidene fluoride-trifluoroethylene)(P(VDF-Tr FE)). We overcame the interfacial layer problem by incorporating P(VDF-Tr FE) as a ferroelectric gate using a low-temperature fabrication process. Our memory devices exhibited excellent memory characteristics with a low programming voltage of ±5 V, a large modulation in channel conductance between ON and OFF states exceeding 105, a long retention time greater than 3 9 104 s, and a high endurance of over 105 programming cycles while maintaining an ION/IOFFratio higher than 102.

基于RFE特征选择的PSO-SVM用电量预测算法

为了提升用电量预测的精度,针对传统支持向量机(SVM)算法在参数确定时的不足,采用粒子群(PSO)算法根据电力应用场景对预测算法进行了改进。对于迭代过程中全局最优和局部最优的矛盾,根据个体适应度的差异进行了子种群划分。而对于粒子群中群体过早收敛的问题,算法引入了自适应变异及惯性权重机制。通过在Schaffer’s F6、Rosenbrock函数上的测试分析结果表明,改进后的PSO算法迭代效率提高了60%以上,达优率也提升了11%。在进行用电量预测时,同时对影响用电量的不同指标进行了特征分析。基于SVM的递归特征消除特性(RFE)筛选了11个影响用电量的指标作为PSO-SVM的模型输入,充分发挥了SVM模型在低维预测上的优势。仿真结果表明,相较于传统SVM算法,所提算法的MAE与RMSE分别提升了9.15%和4.94%。

Large Energy Capacitive High-Entropy Lead-Free Ferroelectrics

Advanced lead-free energy storage ceramics play an indispensable role in next-generation pulse power capacitors market.Here,an ultrahigh energy storage density of~13.8 J cm^(-3)and a large efficiency of~82.4%are achieved in high-entropy lead-free relaxor ferroelectrics by increasing configuration entropy,named high-entropy strategy,realizing nearly ten times growth of energy storage density compared with low-entropy material.Evolution of energy storage performance and domain structure with increasing configuration entropy is systematically revealed for the first time.The achievement of excellent energy storage properties should be attributed to the enhanced random field,decreased nanodomain size,strong multiple local distortions,and improved breakdown field.Furthermore,the excellent frequency and fatigue stability as well as charge/discharge properties with superior thermal stability are also realized.The significantly enhanced comprehensive energy storage performance by increasing configuration entropy demonstrates that high entropy is an effective but convenient strategy to design new high-performance dielectrics,promoting the development of advanced capacitors.