Propagation behavior of elastic waves in one-dimensional piezoelectric/piezomagnetic phononic crystal with line defects

Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating energy reflection/transmittion coefficients of quasi-pressure and quasi-shear waves. Line defects are created by the re- placement of PE or PM constituent layer. The defect modes existing in the first gap are considered and the influences on defect modes of the material properties and volume fraction of the defect layers, the type of incident waves, the location of defect layer and the number of structural layers are discussed in detail. Numerical results indicate that defect modes are the most obvious when the defect layers are inserted in the middle of the perfect PCs; the types of incidence wave and material properties of the defect layers have important effects on the numbers, the location of frequencies and the peaks of defect modes, and the defect modes are strongly de- pendent on volume fraction of the defect layers. We hope this paper will be found useful for the design of PE/PM acoustic filters or acoustic transducer with PCs structures.

Influence of line defects on focusing in a two-dimensional photonic-crystal flat lens

We investigate in detail the influence of line defects on focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens. Through simulations, we find that a focusing can always be observed when a line defect in the lens is introduced along the light transmission direction and the width of the line defect is less than λ/2. However, there appear two focusings when the width of the line defect is more than λ/2. When the line defect is introduced along the direction perpendicular to the transmission, there is always one focusing.

Achieving superior performance in thermoelectric Bi_(0.4)Sb_(1.6)Te_(3.72)by enhancing texture and inducing high-density line defects

Miniaturization of efficient thermoelectric(TE)devices has long been hindered by the weak mechanical strength and insufficient heat-to-electricity conversion efficiency of zone-melted(ZM)ingots.Here,we successfully prepared a robust high-performance p-type Bi_(0.4)Sb_(1.6)Te_(3.72)bulk alloy by combining an ultrafast thermal explosion reaction with the spark plasma sintering(TER-SPS)process.It is observed that the introduced excess Te not only enhances the(00l)-oriented texture to ensure an outstanding power factor(PF)of 5 mW m^(−1)K^(−2),but also induces extremely high-density line defects of up to 10^(11)–10^(12)cm^(−2).Benefiting from such heavily dense line defects,the enhancement of the electronic thermal conductance from the increased electron mobility is fully compensated by the stronger phonon scattering,leading to an evident net reduction in total thermal conductivity.As a result,a superior ZT value of~1.4 at 350 K is achieved,which is 40%higher than that of commercial ZM ingots.Moreover,owing to the strengthening of grain refinement and highdensity line defects,the mechanical compressive stress reaches up to 94 MPa,which is 154%more than that of commercial single crystals.This research presents an effective strategy for the collaborative optimization of the texture,TE performance,and mechanical strength of Bi2Te3-based materials.As such,the present study contributes significantly to the future commercial development of miniature TE devices.

Line defects in monolayer TiSe_(2) with adsorption of Pt atoms potentially enable excellent catalytic activity

Two-dimensional(2D)materials with defects are desired for catalysis after the adsorption of monodispersed noble metal atoms.High-performance catalysts with the absolute value of Gibbs free energy(|△GH|)close to zero,is one of the ultimate goals in the catalytic field.Here,we report the formation of monolayer titanium selenide(TiSe2)with line defects.The low-temperature scanning tunneling microscopy/spectroscopy(STM/S)measurements revealed the structure and electronic states of the line defect.Density functional theory(DFT)calculation results confirmed that the line defects were induced by selenium vacancies and the STM simulation was in good agreement with the experimental results.Further,DFT calculations show that monolayer TiSe_(2) with line defects have good catalytic activity for hydrogen evolution reaction(HER).If the defects are decorated with single Pt atom,the HER catalytic activity will be enhanced dramatically(|△GH|=0.006 eV),which is much better than Pt metal(|△GH|=0.09 eV).Line defects in monolayer TiSe_(2)/Au(111)provide a wonderful platform for the design of high-performance catalysts.

On-Line Defect Detection of Aluminum Coating Using Fiber Optic Sensor

Aluminum metallization using the sprayed coating for exhaust mild steel （MS） pipes of tractors is a standard practice for avoiding rusting. Patches of thin metal coats are prone to rusting and are thus considered as defects in the surface coating. This paper reports a novel configuration of the fiber optic sensor for on-line checking the aluminum metaUization uniformity and hence for defect detection. An optimally chosen high bright 440 nm BLUE LED （light-emitting diode） launches light into a transmitting fiber inclined at the angle of 60° to the surface under inspection placed adequately. The reflected light is transported by a receiving fiber to a blue enhanced photo detector. The metallization thickness on the coated surface results in visually observable variation in the gray shades. The coated pipe is spirally inspected by a combination of linear and rotary motions. The sensor output is the signal conditioned and monitored with RISHUBH DAS. Experimental results show the good repeatability in the defect detection and coating non-uniformity measurement.

管片错台对水工盾构隧洞衬砌受力性能的影响分析

由于盾构隧洞施工环境的复杂性,衬砌管片安装出现的错台问题对隧洞的运行安全产生潜在危害。采用三维有限元方法,建立了衬砌管片—灌浆层—围岩的整体数值模型,考虑管片发生横长轴椭圆度形式的初始安装错台,分析了V类围岩地质条件下的隧洞管片的受力和变形。结果表明,横长轴椭圆度管片错台使底部管片内表面产生较大拉应力,存在受拉开裂的风险;管片局部受压应力和定位销的拉应力有所增大。据此预测了管片受力和变形的最不利位置,对水工盾构隧洞的管片衬砌质量发生错台现象的质量验收具有重要参考价值。

Electron states scattering off line edges on the surface of topological insulator

We study the local density of states （LDOS） for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional （3D） topological insulator （TI） and the line edge of a finite 3D TI, where the front surface and side surface meet with different Fermi velocities, respectively. By using a S-function potential to model the edges, we find that the bound states existed along the step line edge significantly contribute to the LDOS near the edge, but do not modify the exponential behavior away from it. In addition, the power-law decaying behavior for LDOS oscillation away from the step is understood from the spin rotation for surface states scattering off the step defect with magnitude depending on the strength of the potential. Furthermore, the electron refraction and total reflection analogous to optics occurred at the line edge where two surfaces meet with different Fermi velocities, which leads to the LDOS decaying behavior in the greater Fermi velocity side similar to that for a step line edge. However, in the smaller velocity side the LDOS shows a different decaying behavior as x-1/2, and the wavevector of LDOS oscillation is no longer equal to the diameter of the constant energy contour of surface band, but is sensitively dependent on the ratio of the two Fermi velocities. These effects may be verified by STM measurement with high precision.

基于光谱诊断的窄间隙激光填丝焊气孔缺陷检测研究

窄间隙激光焊作为核电领域大型厚壁构件的先进连接工艺,具有热输入小、焊接效率高、接头质量高等优点。然而,受现场复杂施焊环境影响,焊缝内部易因污染物清理不尽而产生气孔缺陷。传统的焊后无损检测费时耗力,且检测结果受零部件尺寸结构制约及检测人员主观判断影响,因此亟待发展气孔缺陷在线检测技术。本文设计研制了基于发射光谱的窄间隙激光焊质量检测系统,探究工艺参数及水、油等污染物对气孔缺陷的影响规律,分析水对激光致等离子体电子温度、光谱强度的作用机制,开发因污染物导致的气孔缺陷在线预警软件系统。结果表明,窄间隙激光焊时由于受工件侧壁拘束使得等离子体密度高,对激光反射、散射作用强,测得光谱强度值较弱。窄间隙填丝焊时由于激光能量存在损耗、不能完全被母材和丝材吸收,其测得的光谱强度小于窄间隙自熔焊。采用Boltzmann作图法求得窄间隙激光填丝焊光致等离子体电子温度为7201.1 K,电子密度为5.2797×10^(15)cm^(-3),均小于窄间隙激光自熔焊时的热力学状态参数。在本文的6组自熔焊工艺参数范围内,X射线探伤未检测到密集气孔缺陷。当母材表面有水时,焊缝表面有气孔产生,通过X射线探伤观察到焊缝中有大量密集气孔存在。与正常工艺下获得的光谱数据相比,光谱仪全波段上的相对光强均降低,电子温度也下降至6900~7200 K范围内动态波动,但电子密度会增大。采用神经网络模型对主成分分析降维后的光谱数据进行训练,可对窄间隙激光填丝焊时因水、油等污染物导致的气孔缺陷进行高准确率的预测。开发的气孔检测系统可对因污染物导致的气孔缺陷进行有效识别,准确率达90%,响应时间在0.1 s内。

基于机器视觉的砂型缺陷检测技术在静压自动造型线中的探索应用

随着对铸件精度要求的不断提高,为了进一步提高铸件质量,在静压自动造型线中,对砂型缺陷的无损在线检测技术展开了探索,并成功将机器视觉应用到砂型缺陷检测中,希望可以为广大铸造行业工作者提供参考。

桥上轨道结构缺陷对无缝线路稳定性影响

桥上护轨对无缝线路稳定性的影响较为复杂,当轨道结构产生缺陷时(道砟缺失、轨枕空吊、扣件失能)会影响无缝线路的稳定性。为了研究桥上轨道结构缺陷对无缝线路稳定性的影响,通过有限元仿真软件,建立铺设护轨的桥上无缝线路有限元模型,研究轨道结构缺陷与无缝线路稳定性之间的关系。研究结果表明:挡砟板破损、轨枕空吊和扣件失能等单一缺陷条件下,均会导致允许升温幅度降低,无缝线路稳定性下降;其在同种工况下,轨枕空吊对应的临界温升幅度略大于扣件失能对应的临界温升幅度;复合缺陷情况下,当扣件失能数量超过2个以后,若扣件失能组数多于轨枕失能根数,则允许升温幅度与轨枕失能根数无关。研究为桥上无缝线路的养护和维修提供理论依据,有助于保证无缝线路服役安全。

The Ultraviolet Detection of Corona Discharge in Power Transmission Lines

Corona discharge is a common phenomenon in power transmission lines external insulation, and it may cause serious defect if without effective detection. The ultraviolet (UV) imagery technology has been widely used to detect the corona discharge in industry in recent years, but some influence factors’ functions are not definite. In this paper, the fracture aluminum strands which is common in power transmission lines were used as the electrode model while a SuperB ultraviolet imager were utilized to detect, the photon count rate was detected with different detect distance, electric field, aluminum strands length and UV gain were applied. Then the multivariate regression analysis (MRA) was taken to calculate the function between the photon count and the factors.

High Precision Ultrasonic Guided Wave Technique for Inspection of Power Transmission Line

Due to the merits of high inspection speed and long detecting distance, Ultrasonic Guided Wave（UGW） method has been commonly applied to the on-line maintenance of power transmission line. However, the guided wave propagation in this structure is very complicated, leading to the unfavorable defect localization accuracy. Aiming at this situation, a high precision UGW technique for inspection of local surface defect in power transmission line is proposed. The technique is realized by adopting a novel segmental piezoelectric ring transducer and transducer mounting scheme, combining with the comprehensive characterization of wave propagation and circumferential defect positioning with multiple piezoelectric elements. Firstly, the propagation path of guided waves in the multi-wires of transmission line under the proposed technique condition is investigated experimentally. Next, the wave velocities are calculated by dispersion curves and experiment test respectively, and from comparing of the two results, the guided wave mode propagated in transmission line is confirmed to be F（1,1） mode. Finally, the axial and circumferential positioning of local defective wires in transmission line are both achieved, by using multiple piezoelectric elements to surround the stands and send elastic waves into every single wire. The proposed research can play a role of guiding the development of highly effective UGW method and detecting system for multi-wire transmission line.

基于改进YOLOv5-LITE轻量级的配电组件缺陷识别

为对配电组件缺陷进行精确快速的定位和识别,提出一种基于改进YOLOv5-LITE轻量级的配电组件缺陷识别方法。为使模型便于部署至移动设备终端,该方法使用ShuffleNetV2作为骨干网提取特征构建YOLOv5-LITE轻量级神经网络模型,并摘除ShuffleNetV2的1024卷积和5×5池化,采用全局平均池化操作替代,降低网络参数量,提升模型检测速度;通过引入有利于细粒度目标检测的152×152特征层,实现了对大、中、小尺度的缺陷检测;在PANet架构中采用深度可分离卷积代替下采样使得网络更加轻量化。实验结果表明:该方法能够识别电缆脱离垫片、电缆与绝缘子脱落、无环绝缘子3种缺陷,其检测精度分别达到92%、95%、95%,网络参数量约为YOLOv5的1/4,检测速度达到2 ms/张。所提出的方法具有实时性、准确率高、轻量化等特点。

格构技术在高铁隧道拱部防水板切割衬砌混凝土缺陷整治中的应用

[目的]许多与高铁隧道衬砌相关的缺陷随着高铁建成年限的增加逐渐凸显,防水板切割衬砌混凝土是其中较为严重的一种缺陷。为了减少结构扰动、降低对线路运行的影响,需采用新技术对高铁隧道拱部防水板切割衬砌缺陷进行整治。[方法]以我国西南地区某设计速度为200 km/h的高铁双线隧道为案例,对其发生拱部防水板切割衬砌混凝土后可采用的2个整治方案(现浇套拱、格构技术)进行了详细分析,并进行了结构的安全性、经济性对比评估。对格构技术缺陷整治方案的施工组织、工艺流程、防护措施及施工效果进行了重点论述。[结果及结论]与其他方案相比,格构技术整治方案充分利用了既有结构的承载能力,仅在局部区域修复隧道,对既有衬砌结构影响较小,对高铁线路的运营影响也较小。该方案能明显降低结构的主应力,减少结构位移,使缺陷衬砌的承载能力满足设计要求。

抽油管的在线漏磁检测技术

由于复杂的工况,抽油管的内、外壁极易发生损伤。目前,抽油管的检测方式主要是将抽油管抽离油井后送至后线检测场地进行检测,造成了时间、人力、物力的浪费。采用漏磁检测方法,开展了抽油管在起管或下管过程中的在线检测;设计了瓦片式磁化结构,建立抽油管漏磁检测的三维仿真模型;针对抽油管的腐蚀缺陷,改变缺陷尺寸参数,研究了缺陷漏磁场的分布特性;研发了抽油管在线漏磁检测系统,在实验室和油田作业现场对抽油管进行在线检测试验。试验结果表明,该系统能够快速高效地完成抽油管的在线检测,为抽油管的损伤监测提供了一些参考。

基于深度学习的计算机视觉在隧道衬砌病害检测中的应用综述

隧道衬砌作为隧道的重要支撑结构,对其中存在的病害进行检测显得十分重要。然而,传统的隧道病害检测方法高度依赖人工,效率低下,并且存在一定的安全风险,因此,如何高效、安全地实现病害的自动检测成为了热门的方向之一。深度学习(DL)和计算机视觉(CV)被视为实现隧道衬砌病害自动检测的具有发展前景的方法。为了阐明DL技术和CV技术在病害检测中的研究与应用,总结了隧道衬砌病害检测技术的发展历程;基于数据对于DL模型训练的重要性,总结了衬砌病害数据集的建立过程;随后,总结了基于DL的CV技术在隧道衬砌表面病害和内部病害检测方面的方法和应用;最后,讨论了目前研究中存在的问题,并对未来的发展进行了展望。

Observation of parabolic electron bands on superconductor LaRu_(2)As_(2)

Ru-based superconductor LaRu_(2)As_(2) has been discovered exhibiting the highest critical temperature of ~ 7.8 K among iron-free transition metal pnictides with the ThCr_(2)Si_(2)-type crystal structure. However, microscopic research on this novel superconducting material is still lacking. Here, we utilize scanning tunneling microscopy/spectroscopy to uncover the superconductivity and surface structure of LaRu_(2)As_(2). Two distinct terminating surfaces are identified on the cleaved crystals, namely, the As surface and the La surface. Atomic missing line defects are observed on the La surface. Both surfaces exhibit a superconducting gap of ~ 1.0 me V. By employing quasiparticle interference techniques, we observe standing wave patterns near the line defects on the La atomic plane. These patterns are attributed to quasiparticle scattering from two electron type parabolic bands.

基于改进YOLOv8与语义知识融合的金具缺陷检测方法研究

针对输电线路螺栓金具缺陷检测任务中存在的缺陷样本类间分布不均、缺陷微小特征提取困难等问题,提出基于改进YOLOv8和语义知识融合的输电线路螺栓缺陷检测方法。首先,通过深入分析数据样本中螺栓金具缺陷种类与该螺栓承载金具种类之间的关系,完成语义关联构建工作;之后,在YOLOv8模型Neck部分引入BiFusion和RepBlock模块,增强模型的特征提取能力;其次,使用改进的融合语义知识校正权重的Loss函数,进一步提高训练模型的准确性,减少误检的发生;最后,分别完成基线选取实验、消融实验、超参数调整实验以及对比实验。实验结果表明,相较于Baseline模型,改进YOLOv8方法在平均精确率(mAP)上提升了4.0%,在关键少样本类精确率上提升了24.6%,可有效提高输电线路螺栓金具缺陷检测的效果,该语义关联构建及语义知识融合方法具有一定的泛用性,为输电线路无人机智能巡检领域提供了新的方法支持。

Constructing a data platform for surface defect management using a multidimensional database

Surface quality has been one of the key factors influencing the ongoing improvement of the quality of steel. Therefore,it is urgent to provide methods for efficient supervision of surface defects. This paper first expressed the main problems existing in defect management and then focused on constructing a data platform of surface defect management using a multidimensional database. Finally, some onqine applications of the platform at Baosteel were demonstrated. Results show that the constructed multidimensional database provides more structured defect data, and thus it is suitable for swift and multi-angle analysis of the defect data.

不锈钢内衬修复复合管层间缺陷处应力分析

为研究不锈钢内衬修复前后复合管道内腐蚀缺陷处的应力分布规律以及修复效果,基于有限元软件,建立含单腐蚀坑缺陷的管道模型,改变腐蚀坑的深厚比,忽略黏结层厚度及对腐蚀坑的填补影响,层间采用黏接行为建立界面相互作用分析模型,将修复前后腐蚀缺陷处的应力进行对比。随着腐蚀缺陷深厚比的增加,管壁腐蚀缺陷处的径向应力、周向应力、Mises应力都有增大的趋势;修复前缺陷处的周向应力最大,且其值与Mises应力相近;经不锈钢内衬修复后,缺陷处的周向应力下降了11.3%,Mises应力下降了7.12%。腐蚀缺陷的深厚比对管道的应力分布有着显著的影响,所以在进行复合管线安全评估时应注意腐蚀深度的影响;在修复前后,管道腐蚀缺陷处的控制应力一直是周向应力,复合管道的失效可依据周向应力进行判断;经不锈钢内衬修复后,原始缺陷处的应力发生了重分布,其周向应力与Mises应力均有减小,修复效果明显。