Ultrafast dynamics in photo-excited Mott insulator Sr_(3)Ir_(2)O_7 at high pressure

High-pressure ultrafast dynamics,as a new crossed research direction,are sensitive to subtle non-equilibrium state changes that might be unresolved by equilibrium states measurements,providing crucial information for studying delicate phase transitions caused by complex interactions in Mott insulators.With time-resolved transient reflectivity measurements,we identified the new phases in the spin–orbit Mott insulator Sr_(3)Ir_(2)O_7 at 300 K that was previously unidentified using conventional approaches such as x-ray diffraction.Significant pressure-dependent variation of the amplitude and lifetime obtained by fitting the reflectivity?R/R reveal the changes of electronic structure caused by lattice distortions,and reflect the critical phenomena of phase transitions.Our findings demonstrate the importance of ultrafast nonequilibrium dynamics under extreme conditions for understanding the phase transition of Mott insulators.

Quantitative determination of the critical points of Mott metal–insulator transition in strongly correlated systems

Mottness is at the heart of the essential physics in a strongly correlated system as many novel quantum phenomena occur in the metallic phase near the Mott metal–insulator transition. We investigate the Mott transition in a Hubbard model by using the dynamical mean-field theory and introduce the local quantum state fidelity to depict the Mott metal–insulator transition. The local quantum state fidelity provides a convenient approach to determining the critical point of the Mott transition. Additionally, it presents a consistent description of the two distinct forms of the Mott transition points.

Optical study of magnetic topological insulator MnBi_(4)Te_7

We present an infrared spectroscopy study of the magnetic topological insulator MnBi_(4)Te_7 with antiferromagnetic(AFM) order below the Neel temperature TN= 13 K. Our investigation reveals that the low-frequency optical conductivity consists of two Drude peaks, indicating a response of free carriers involving multiple bands. Interestingly, the narrow Drude peak grows strongly as the temperature decreases, while the broad Drude peak remains relatively unchanged. The onset of interband transitions starts around 2000 cm^(-1), followed by two prominent absorption peaks around 10000 cm^(-1) and 20000 cm^(-1). Upon cooling, there is a notable transfer of spectral weight from the interband transitions to the Drude response. Below TN, the AFM transition gives rise to small anomalies of the charge response due to a band reconstruction.These findings provide valuable insights into the interplay between magnetism and the electronic properties in MnBi_(4)Te_7.

Data augmentation method for insulators based on Cycle-GAN

Data augmentation is an important task of using existing data to expand data sets.Using generative countermeasure network technology to realize data augmentation has the advantages of high-quality generated samples,simple training,and fewer restrictions on the number of generated samples.However,in the field of transmission line insulator images,the freely synthesized samples are prone to produce fuzzy backgrounds and disordered samples of the main insulator features.To solve the above problems,this paper uses the cycle generative adversarial network(Cycle-GAN)used for domain conversion in the generation countermeasure network as the initial framework and uses the self-attention mechanism and channel attention mechanism to assist the conversion to realize the mutual conversion of different insulator samples.The attention module with prior knowledge is used to build the generation countermeasure network,and the generative adversarial network(GAN)model with local controllable generation is built to realize the directional generation of insulator belt defect samples.The experimental results show that the samples obtained by this method are improved in a number of quality indicators,and the quality effect of the samples obtained is excellent,which has a reference value for the data expansion of insulator images.

A Simple and Effective Surface Defect Detection Method of Power Line Insulators for Difficult Small Objects

Insulator defect detection plays a vital role in maintaining the secure operation of power systems.To address the issues of the difficulty of detecting small objects and missing objects due to the small scale,variable scale,and fuzzy edge morphology of insulator defects,we construct an insulator dataset with 1600 samples containing flashovers and breakages.Then a simple and effective surface defect detection method of power line insulators for difficult small objects is proposed.Firstly,a high-resolution featuremap is introduced and a small object prediction layer is added so that the model can detect tiny objects.Secondly,a simplified adaptive spatial feature fusion(SASFF)module is introduced to perform cross-scale spatial fusion to improve adaptability to variable multi-scale features.Finally,we propose an enhanced deformable attention mechanism(EDAM)module.By integrating a gating activation function,the model is further inspired to learn a small number of critical sampling points near reference points.And the module can improve the perception of object morphology.The experimental results indicate that concerning the dataset of flashover and breakage defects,this method improves the performance of YOLOv5,YOLOv7,and YOLOv8.In practical application,it can simply and effectively improve the precision of power line insulator defect detection and reduce missing detection for difficult small objects.

Higher-order topological Anderson insulator on the Sierpiński lattice

Disorder effects on topological materials in integer dimensions have been extensively explored in recent years. However, its influence on topological systems in fractional dimensions remains unclear. Here, we investigate the disorder effects on a fractal system constructed on the Sierpiński lattice in fractional dimensions. The system supports the second-order topological insulator phase characterized by a quantized quadrupole moment and the normal insulator phase. We find that the second-order topological insulator phase on the Sierpiński lattice is robust against weak disorder but suppressed by strong disorder. Most interestingly, we find that disorder can transform the normal insulator phase to the second-order topological insulator phase with an emergent quantized quadrupole moment. Finally, the disorder-induced phase is further confirmed by calculating the energy spectrum and the corresponding probability distributions.

Three-dimensional topological crystalline insulator without spin-orbit coupling in nonsymmorphic photonic metacrystal

By including certain point group symmetry in the classification of band topology,Fu proposed a class of threedimensionaltopological crystalline insulators(TCIs)without spin-orbit coupling in 2011.In Fu’s model,surface states(ifpresent)doubly degenerate atГandM when time-reversal and C4 symmetries are preserved.The analogs of Fu’s modelwith surface states quadratically degenerate atM are widely studied,while surface states with quadratic degeneracy atГare rarely reported.In this study,we propose a three-dimensional TCI without spin-orbit coupling in a judiciously designednonsymmorphic photonic metacrystal.The surface states of photonic TCIs exhibit quadratic band degeneracy in the(001)surface Brillouin zone(BZ)center(Гpoint).The gapless surface states and their quadratic dispersion are protected by C4and time-reversal symmetries,which correspond to the nontrivial band topology characterized by Z_(2)topological invariant.Moreover,the surface states along lines fromГto the(001)surface BZ boundary exhibit zigzag feature,which is interpretedfrom symmetry perspective by building composite operators constructed by the product of glide symmetries with timereversalsymmetry.The metacrystal array surrounded with air possesses high order hinge states with electric fields highlylocalized at the hinge that may apply to optical sensors.The gapless surface states and hinge states reside in a cleanfrequency bandgap.The topological surface states emerge at the boundary of the metacrystal and perfect electric conductor(PEC),which provide a pathway for topologically manipulating light propagation in photonic devices.

Pressure induced insulator to metal transition in quantum spin liquid candidate NaYbS_(2)

Pressure induced insulator to metal transition followed by the appearance of superconductivity has been observed recently in inorganic quantum spin liquid candidate NaYbSe_(2).In this paper,we study the properties of isostructural compound NaYbS_(2)under pressure.It is found that the resistance of Na YbS_(2)single crystal exhibits an insulating state below 82.9 GPa,but with a drop of more than six orders of magnitude at room temperature.Then a minimum of resistance is observed at about 100.1 GPa and it moves to lower temperature with further compression.Finally,a metallic state in the whole temperature range is observed at about 130.3 GPa accompanied by a non-Fermi liquid behavior below 100 K.The insulator to metal transition,non-monotonic resistance feature and non-Fermi liquid behavior of NaYbS_(2)under pressure are similar to those of NaYbSe_(2),suggesting that these phenomena might be the universal properties in NaLnCh_(2)(Ln=rare earth,Ch=O,S,Se)system.

Thermal Hall effect and the Wiedemann–Franz law in Chern insulator

Thermal Hall effect, where a transverse temperature difference is generated by implementing a longitudinal temperature gradient and an external magnetic field in the perpendicular direction to systems, is a useful tool to reveal transport properties of quantum materials. A systematic study of the thermal Hall effect in a Chern insulator is still lacking. Here,using the Landauer–Büttiker formula, we investigated the thermal Hall transport of the Harper–Hofstadter model with flux φ= 1/2 and its generalizations. We demonstrated that the Wiedemann–Franz law, which states that the thermal Hall conductivity is linearly proportional to the quantum Hall conductivity in the low temperature limit, is still valid in this Chern insulator, and that the thermal Hall conductivity can be used to characterize the topological properties of quantum materials.

Measurement of alumina film induced ablation of internal insulator in solid rocket environment

This study investigates the ablation of internal insulation induced by the deposition of an alumina film with different lateral film speeds.A sub-scale test solid rocket motor(SRM)was designed in an impinging jet configuration to form an alumina film on the sample and to encourage the lateral movement of the film by a high-speed wall jet.Fifteen static fire tests of the test SRM were conducted with six different jet velocities(V_(jet)=100 m/s,150 m/s,200 m/s,268 m/s,330 m/s,and 450 m/s)that indirectly affected the velocity of the wall jet and the deposition rate of alumina droplets.The ablation velocity was deduced from the difference in the sample thickness after a test using a coordinate measuring machine.The droplet deposition mass flux and wall jet velocity were obtained via two-phase flow simulation with the same jet velocity and effective pressure.As a result,the characteristics of alumina-induced ablation and the changes in ablation with jet velocities were obtained.The area within0.8×jet diameter was focused upon,where the ratio of ablation velocity to incoming alumina mass was constant for each jet velocity,and showed a similarity in jet structure.When the ablation velocity was increased from 2.05 to 9.98 mm/s with increasing jet velocity,the ratio of the ablation velocity and alumina mass flux decreased from 1.07×10^(-4)to 0.49×10^(-4)m^(3)/kg as Al_(2)O_(3)-C reactions became less efficient with a reduced residence time of the film.Because the decrease in residence time by the wall jet is more pronounced for slow reactions involved in Al_(2)O_(3)-C reactions,fast reactions in Al_(2)O_(3)-C reactions are less affected and result in a convergence of the volumetric rate of ablation per unit mass of alumina.

Magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulators

Control and detection of antiferromagnetic topological materials are challenging since the total magnetization vanishes.Here we investigate the magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulator Mn Bi2Te4.We find that by breaking the combined mirror symmetries with either perpendicular electric field or external magnetic moment,Kerr and Faraday effects occur.Under perpendicular electric field,antiferromagnetic topological insulators(AFMTI)show sharp peaks at the interband transition threshold,whereas trivial insulators show small adjacent positive and negative peaks.Gate voltage and Fermi energy can be tuned to reveal the differences between AFMTI and trivial insulators.We find that AFMTI with large antiferromagnetic order can be proposed as a pure magneto-optical rotator due to sizable Kerr(Faraday)angles and vanishing ellipticity.Under external magnetic moment,AFMTI and trivial insulators are significantly different in the magnitude of Kerr and Faraday angles and ellipticity.For the qualitative behaviors,AFMTI shows distinct features of Kerr and Faraday angles when the spin configurations of the system change.These phenomena provide new possibilities to optically detect and manipulate the layered topological antiferromagnets.

Numerical Simulation of Contamination Accumulation Characteristics of Composite Insulators in Salt Fog Environment

To investigate the fouling characteristics of the composite insulator surface under the salt fog environment,the FXBW-110/120-2 composite insulator was taken as the research object.Based on the field-induced charge mechanism,the multi-physical field coupling software COMSOL was used to numerically simulate the fouling characteristics,explored the calculation method of ESDD,and demonstrated its rationality.Based on this method,the pollution characteristics of the composite insulator under the pollution fog environment were studied,and the influence of wind speed,droplet size,and voltage type on the pollution characteristics of the composite insulator was analyzed.The results showed that:with the increase in wind speed,the amount of accumulated pollution of insulator increases in the range of droplet size,and the relationship between wind speed and accumulated pollution is approximately linear;at the same wind speed,the amount of accumulated pollution increases with the increase of droplet size under the action of DC voltage;when there is no voltage,the amount of dirt on the upper surface of the insulator is more than that on the lower surface,while it is the opposite under DC voltage.

基于轻量化网络与增强多尺度特征融合的绝缘子缺陷检测

随着无人机搭载目标检测算法在输电杆塔绝缘子巡检领域的发展,针对绝缘子缺陷检测速度较低,网络复杂度高且缺陷小目标难以准确检测的问题,提出一种基于轻量化网络与增强多尺度特征融合的YOLOv5-3S-4PH模型进行绝缘子缺陷实时检测。首先将重构的ShuffleNetV2-Stem-SPP(3S)网络作为YOLOv5的主干网络,显著减小了网络的参数量和计算量;其次引入针对小目标的增强多尺度特征融合网络以及4个预测头,来增强网络对绝缘子缺陷的感知能力,并结合Mosaic-9数据增强、CIoU损失函数进一步补偿轻量化导致的检测精度损失;最后将其应用到自制绝缘子数据集进行验证。实验结果表明,该文所提出的模型相对于未改进的YOLOv5,全类平均精度提高了3%,检测速度提高了81.8%,参数量、计算量分别压缩了82.4%、67%。因此,所提出的模型更适合部署在无人机平台上进行绝缘子缺陷的实时监测。

高海拔高速运行高铁车顶绝缘子风压分布及海拔修正

车顶绝缘子是高铁动车组列车重要的组成部件,高海拔地区运行中车顶绝缘子在高速气流作用下周围风压分布形成负压区导致其综合气压远低于实际海拔对应的气压进而影响车顶绝缘子电气性能。该文基于计算流体力学(computational fluid dynamics,CFD),建立仿真模型,分析高速气流作用下车顶绝缘子周围风压分布特性及影响因素,并提出高海拔高速气流综合作用下车顶绝缘子电气强度修正方法。结果表明:车顶绝缘子的风压低值分布在侧风面伞裙根部(大伞在下表面根部,小伞在上表面根部);迎风面风压、背风面和侧风面风压的绝对值都随风速的增大呈指数增长,且海拔越低,增长越快;攻角为80°左右时将形成更明显的低压区;海拔4000m、运行速度为360km/h综合作用下车顶绝缘子形成负压相当于4599米海拔对应的气压,车顶绝缘子外绝缘修正应予以考虑。

基于局部特征深度信息的绝缘子小样本缺陷检测

基于深度学习的目标检测技术已广泛应用于绝缘子缺陷检测中,然而现有目标检测算法主要基于大量缺陷样本训练网络模型,无法对少样本缺陷进行准确识别。针对绝缘子缺陷检测过程中缺陷样本量不足的问题,该文提出了一种基于局部特征深度信息的绝缘子小样本缺陷检测方法。首先采用旋转目标检测网络改进Faster R-CNN(faster region-based convolutional neural network)模型提取绝缘子串区域,然后对绝缘子串特征进行划分,提取绝缘子串局部特征并基于深度推土距离(deep earth mover’s distance,Deep EMD)网络实现小样本缺陷检测。实验结果表明,在玻璃绝缘子自爆缺陷检测中,所提出方法采用2张训练样本可取得与现有目标检测方法 200张训练样本相同的效果,采用10张训练样本的绝缘子自爆检测在与真值框的交并比阈值为0.5至0.95之间的平均精度(mean average precision,mAP)达到0.65,该方法为小样本电力设备缺陷智能化检测提供了新的方法和思路。

菌丝体-杨木颗粒多孔复合材料的制备及保温阻燃性能研究

石油基高分子多孔材料的大量使用导致了严重的塑料污染(“白色污染”)。在这项工作中,采用了一种绿色可持续的合成策略,通过在杨木颗粒上接种培养真菌菌丝体,使其生长贯穿整个颗粒,最终制备出了一种菌丝体-杨木颗粒多孔复合材料。结果表明,多孔复合材料具有较低的密度(0.165 g·cm^(-3))、较高的孔隙率(82.7%)和疏水性(接触角:131.8°),并展示出优异的力学性能(压缩强度2.39 MPa;杨氏模量9.79 MPa)。另外,多孔复合材料还具有较低的导热系数(0.066 W/mK)和优异的阻燃性能(氧指数为28.4%)。这项研究工作展示了一种简捷和清洁环保的菌丝体-杨木颗粒多孔复合材料制备方法,对农林生物质高值化利用具有重要的参考价值。

轻质高绝缘复合芯体制备及其在66 kV复合横担中的应用

随着“双碳”战略的逐步落实,新型复合材料横担正逐步代替铁制横担,在电力线路中的应用日益广泛。文中制备得到密度为1.1 g/cm^(3)的66 kV轻质高绝缘复合绝缘横担,并对其进行吸水率、染料渗透、水扩散泄漏电流、击穿强度、热诱导、机械及电气试验。试验结果表明:填充芯体材料样品的质量吸水率为0.141%,水扩散泄漏电流小于103.3μA,交流击穿强度大于71 kV/cm,各项性能指标均达到DL/T 1580—2016棒形复合绝缘子用芯棒技术规范对于理化性能、电气性能及机械性能的标准要求,样品及横担整体无明显缺陷,横担耐老化性较好。同时,轻质高绝缘复合绝缘横担微观界面结合良好,绝缘性能优于传统实心横担,满足新型电力系统清洁低碳、安全可靠的应用需求。

高性能有机硅灌封胶的制备与性能研究

以端乙烯基硅油(1000 mPa·s)和侧乙烯基硅油(500 mPa·s)复配为基体树脂,含氢硅油为固化剂,乙烯基硅烷偶联剂为增黏剂,乙烯基MQ树脂和气相白炭黑为补强材料,氢氧化镁和硅系阻燃剂(FCA-107)为阻燃填料,成功制备了一款具有无卤阻燃特性及优异力学性能和电气绝缘性能的有机硅灌封胶,并研究了硅油复配比例、各填料添加量对有机硅灌封胶性能的影响。结果表明:当端乙烯基硅油与侧乙烯基硅油的复配比例为5∶5,乙烯基硅烷偶联剂质量分数为3%,气相白炭黑质量分数为4%,乙烯基MQ树脂质量分数为30%,复配阻燃剂质量分数为20%时,有机硅灌封胶的综合性能达到最佳,其混合黏度为1842 mPa·s,拉伸强度为2.83 MPa,断裂伸长率为51.3%,拉伸剪切强度为2.12MPa,阻燃性能(UL 94)达到V-0级,电气强度达到24.3 kV/mm,体积电阻率为3.8×10^(15)Ω·cm,制备的有机硅灌封胶可以满足电子元器件的发展要求。

装配式日光温室柔性复合墙体性能测试与分析

为解决装配式日光温室柔性墙体蓄热能力不足的问题,该研究通过在墙体内侧附加蓄热层的方式,设计了一种集蓄热、保温和防水多功能于一体的装配式柔性复合墙体。首先,通过对多种材料进行综合性能评估,筛选出优质的表层材料和保温材料,将其复合制成柔性保温墙体;其次,将水、沙子、相变水凝胶(phase change hydrogel,PCH)作为蓄热层固定在柔性保温墙体内侧,从而形成柔性复合墙体;最后,在4个模型温室中分别对墙体进行性能测试,以未附加蓄热层的柔性保温墙体为对照(CK),分析试验墙体的蓄热和保温性能。单一墙体材料的性能测试结果表明,表层材料中镀铝编织布、黑色淋膜毡抗拉性能好且不透水,断裂强力分别为1.06、0.56 kN,断裂伸长率分别为30.99%、65.91%;保温材料中再生棉、太空棉和空气柱保温效果较好且使用成本低,热阻值分别为0.30、0.50、0.76(m^(2)·℃)/W。柔性复合墙体的性能测试结果表明,所有处理中5 kg/m^(2) PCH柔性复合墙体的蓄热和保温性能最佳,热阻值为2.50(m^(2)·℃)/W,单位面积累计吸热量与放热量分别为1.48、1.13 MJ/m^(2);在典型晴天和阴天条件下,该处理的夜间室内平均温度分别比CK提高了3.08、1.87℃。上述分析结果表明,通过在柔性保温墙体内侧附加相变蓄热层的方式,能够增强墙体的蓄热和保温性能。研究结果可为今后装配式日光温室柔性复合墙体设计及材料选择提供理论依据。

模卡砌块组合保温墙体热工性能及其经济性分析

随着超低能耗建筑、近零能耗及零能耗建筑的发展,新型外墙围护结构引起广泛地研究和重视.模卡砌块作为一种新型外墙自保温技术,开始在上海、江苏等国内一些发达地区被试点和应用,但目前暂无相应规范指导,其热工性能及经济性仍缺乏系统性研究.文中以夏热冬冷地区某公共建筑为例,采用DeST能耗模拟软件,建立了传统外保温墙体、模卡砌块组合保温墙体三维分析模型,研究了膨胀聚苯板、岩棉板、聚氨酯板、挤塑聚苯板4种不同类型保温材料及6种不同厚度(30、50、70、90、110、130 mm)下模卡砌块组合保温墙体的热工性能.进一步,采用净现值法,对不同工况下的砌块组合保温墙体进行了经济性分析.研究表明:在相同外墙保温厚度下,聚氨酯板的保温效果最佳;不同保温材料厚度对应的净现值都呈现出先上升后下降的趋势,结合净现值和节能率,其最优厚度分别为70、70、40、60 mm,对应的节能率分别在达到我国建筑节能65%的标准上再降低7.08%、6.81%、5.1%、6.5%.