Guided Wave Based Damage Detection Method for Aircraft Composite Structures under Varying Temperatures

Guided waves based damage detection methods using base signals offer the advantages of simplicity of signal generation and reception,sensitivity to damage,and large area coverage;however,applications of the technology are limited by the sensitivity to environmental temperature variations.In this paper,a Spearman Damage Index-based damage diagnosis method for structural health condition monitoring under varying temperatures is presented.First,a PZT sensor-based Guided wave propagation model is proposed and employed to analyze the temperature effect.The result of the analysis shows the wave speed of the Guided wave signal has higher temperature sensitivity than the signal fluctuation features.Then,a Spearman rank correlation coefficient-based damage index is presented to identify damage of the structure under varying temperatures.Finally,a damage detection test on a composite plate is conducted to verify the effectiveness of the Spearman Damage Index-based damage diagnosis method.Experimental results show that the proposed damage diagnosis method is capable of detecting the existence of the damage and identify its location under varying temperatures.

Identification Method for Users-Transformer Relationship in Station Area Based on Local Selective Combination in Parallel Outlier Ensembles Algorithm

In the power distribution system,the missing or incorrect file of users-transformer relationship(UTR)in lowvoltage station area(LVSA)will affect the leanmanagement of the LVSA,and the operation andmaintenance of the distribution network.To effectively improve the lean management of LVSA,the paper proposes an identification method for the UTR based on Local Selective Combination in ParallelOutlier Ensembles algorithm(LSCP).Firstly,the voltage data is reconstructed based on the information entropy to highlight the differences in between.Then,the LSCP algorithmcombines four base outlier detection algorithms,namely Isolation Forest(I-Forest),One-Class Support VectorMachine(OC-SVM),Copula-Based Outlier Detection(COPOD)and Local Outlier Factor(LOF),to construct the identification model of UTR.This model can accurately detect users’differences in voltage data,and identify users with wrong UTR.Meanwhile,the key input parameter of the LSCP algorithm is determined automatically through the line loss rate,and the influence of artificial settings on recognition accuracy can be reduced.Finally,thismethod is verified in the actual LVSA where the recall and precision rates are 100%compared with othermethods.Furthermore,the applicability to the LVSAs with difficult data acquisition and the voltage data error in transmission are analyzed.The proposed method adopts the ensemble learning framework and does not need to set the detection threshold manually.And it is applicable to the LVSAs with difficult data acquisition and high voltage similarity,which improves the stability and accuracy of UTR identification in LVSA.

基于CFD-DEM的排种器仿真及参数优化

对于蔬菜种植而言,提高机械化播种的精度是关键的突破口,能够起到节本增效的作用。为提高排种器的排种性能,采用计算流体力学与离散单元法(CFD-DEM)耦合仿真技术对排种器的试验因素进行性能仿真。同时,分析种子在不同吸嘴结构和作业参数下的运动特性。为探究最佳的参数组合,利用中心复合设计(CCD)试验方案去探究吸嘴锥角、种盘角速度以及负压对排种合格率和漏播率这两个试验指标的影响。仿真试验结果的方差分析表明:负压对合格率和漏播率的影响最大,吸嘴锥角和种盘角速度的影响次之。随后,通过建立参数化数学模型确定参数优化区域。参数优化结果表明:在锥角为50°,负压在4.87~5.64 kPa以及角速度在1.67~1.95 rad/s范围内,排种合格率大于95%,漏播率小于2.5%。通过台架验证试验得出的结果与优化结果基本一致,表明优化结果合理可信。本文的仿真和参数优化结果可为今后排种器的研制提供参考。

Enhancing Photovoltaic Performance of Ladder-Type Heteroarene-Based Electron Acceptors by Modulating Molecular Packing

Comprehensive Summary,The development of novel building blocks with sp3-hybridized-carbon-free conjugated skeletons is important to further advance and enrich nonfullerene acceptors(NFAs),but this remains a challenge due to the lack of strategies to effectively modulate the aggregation behavior of resulting NFAs.Herein,two novel nitrogen-bridged octacyclic ladder-type heteroarenes end-capped with thiophene rings(BTPS)or selenophene rings(BTPSe)are designed and synthesized as the donor cores for constructing NFAs(MQX-2 and MQX-4).It is found that replacing the sulfur atoms(MQX-2)at the outer positions of the heteroarene core with selenium atoms(MQX-4)can effectively modulate the molecular packing mode of the NFAs.The incorporation of selenium atoms induces stronger O···Se noncovalent interaction than O···S,thus promoting the formation of mixed H/J-type aggregates in MQX-4.Benefiting from more electron hopping channels,MQX-4 exhibits higher electron transport(more than 1-fold enhancement)and photovoltaic properties compared to MQX-2,which forms only H-type aggregates.

Impact of regio-isomeric monochlorinated end groups on packing mode,miscibility,and photovoltaic performance of asymmetric selenophene-fused M-series acceptors

Optimal bulk-heterojunction(BHJ)morphology is crucial for efficient charge transport and good photovoltaic performance in organic solar cells(OSCs).Yet,the correlation between chemical structures of nonfullerene acceptors(NFAs)and molecular interaction in the BHJ blends remains opaque.Herein,we study three isomeric NFAs referred to as MQ1-x(x=β,y,or 8)that shared an asymmetric selenophene-fused heteroheptacene backbone end-capped by two monochlorinated end groups.Remarkably,miscibility between the polymer donor of PM6 and MQ1-x successively elevates as the chlorine atoms move fromβ-,to y-,to 8-position of terminals.Combined with the varied molecular crystallinity of these NFAs,diverse BHJ morphologies are observed in their blend films.As a result,the MQ1-8-based devices present the highest PCE of 12.08%owing to the efficient charge dissociation and transport induced by the compact molecular packing and optimal BHJ morphology.Our investigation provides a new insight in the material design that has a good balance in molecular packing and film morphology for high-performance OSCs.

Highly Conductive Poly(Imide–Imine)Hybrid Vitrimer-Graphene Aerogel Composites

Comprehensive Summary,Although polyimides(PIs)have shown great potential for a broad range of applications,it remains very challenging to achieve the malleability,rehealability and recyclability for PIs and their composites targeting various applications,particularly for the rapidly emerging flexible and stretchable electronics.Herein,malleable conductive poly(imide-imine)hybrid(PIIH)vitrimer-graphene aerogel(GA)composites have been prepared,for the first time,via simple sol-gel film formation followed by heat-press.The resulting PIIH-GA composites exhibit not only the highly desired properties of thermosetting(strong mechanical strength)and thermoplastic(reprocessability)polymers,but also good conductivity enabled by the GA filler.PIIH3-GA-10(with 10 wt%GA)showed one of the highest electrical conductivities(26.7 S/m)for PI-based composites,as well as good electromagnetic interference(EMI)shielding performance.Moreover,the PIIH-GA films could maintain good performance during stretching and even after chemical recycling,which opens new opportunities for flexible and sustainable electronics development.

Monolithic polyimine vitrimer/graphene aerogel composites

Graphene-polymer composites have attracted great attention as sensing materials due to their tailorable electrical conductivity, physicochemical properties, and sensitivity to geometric and functional changes.Herein, we report the first example of cylindrical monolithic polyimine vitrimer/graphene composites with excellent mechanical, compressive, rehealable and recyclable, and piezoresistive properties via simple infiltration of polymer monomers into the pores of graphene aerogel followed by thermal curing. The composites exhibit excellent durable compressibility(negligible reduction in the compression properties even after 3000 consecutive compression cycles), rapid recovery to the original size upon stress released,high compressive strength(up to 1.2 MPa), and high conductivity(up to 79 S/m). Excellent piezoresistive properties were observed, displaying consistent and reliable change of the electrical resistance with the compression ratio. Furthermore, rehealing with ~100% recovery of the compressive strength and electric conductivity was achieved under mild rehealing conditions, which is highly desired but has rarely been reported for electronic materials. The facile strategy for fabrication of rehealable monolithic polymer/GAs can open new possibilities for the sustainable development of composites with high electrical conductivity for various applications such as sensing, health monitoring, and movement detection.

Video-based pedestrian grouping model considering longspan space in a big hall

Pedestrian group detection is a challenging but significant issue in pedestrian flow control and public safety management.To address the issue that most conventional pedestrian grouping models(PGMs)can only identify a pedestrian group at a limited distance of less than 2 m,this study extended the pedestrian distance constraint of conventional PGMs with a reconstruction of the normal group detection criterion and development of a novelgroup detection criterion suitable for long-span space.To measure the movement behaviorsimilarity with normal distance,five necessary constraints:velocity difference,moving direction offset,distance limitation,distance fluctuation,and group-keeping duration were studied quantitatively to form the criterion to detect normal groups.Meanwhile,a long-span group detection criterion was proposed with extended distance and direction con-sistency constraints.Therefore,this study proposed an improved PGM that considers long-span spaces(PGMLS).In the PGMLS workflow,the MMTrack algorithm was used to obtainpedestrian trajectories.A difference measurement method based on sequential pattern analysis(SPA)was adopted to analyze the velocity similarity of pedestrians.To validate the proposed grouping model,experiments based on pedestrian movement videos in the exit hall of the Shanghai Hongqiao International Airport were conducted.The results indicate that the proposed model can detect both normal and widely separated pedestrian groups,with a long span range of 2-12 m.

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Asymmetric nonfullerene acceptors(NFAs)possess larger dipole moments and stronger intermolecular bonding energy than their symmetric counterparts thereby making them promising candidates for high-performance polymer solar cells(PSCs).Herein,we report twoefficient acceptor–donor–acceptor(A–D–A)type NFAs(M14 and M18)with asymmetric side chains that show enhanced intermolecular interactions compared with their corresponding counterparts(M17 and M19)based on symmetric side chains.Furthermore,M14 and M18 exhibit elevated lowest unoccupiedmolecular orbitals and smallerπ–πstacking distances in comparison with M17 and M19,respectively.In combination with the benchmark polymer donor of PM6,the PM6:M14 blend affords superior charge transport properties,and more importantly,an increased power conversion efficiency(PCE)of 15.49%in comparison with the M17-based counterpart(13.01%PCE).Similarly,the asymmetric M18-based blend also shows a higher PCE of 13.00%than the M19-based blend(11.55%).Through further interface engineering,the bestperforming M14-based device delivers an enhanced PCE of 16.46%,which represents a record value among all asymmetric A–D–A type NFAs.Our results provide new insights into the design of asymmetric NFAs with enhanced intermolecular interactions for highperformance PSCs.

Revealing the spacing effect of neighboring side-chains in modulating molecular aggregation and orientation of M-series acceptors

Controlling the aggregation of small-molecule acceptors(SMAs)is essential to obtain an optimal morphology and to improve the photovoltaic performance of polymer solar cells(PSCs).However,reducing intermolecular aggregation of SMAs is usually accompanied by the disruption of compact molecular packing thereby leading to their decreased electron mobilities.Here,two novel M-series SMAs(MD1T and MD2T)based on ladder-type heterononacenes with neighboring side-chains separated by one or two thiophene rings are designed and synthesized.It is found that shortening the spacing of the neighboring side-chains of the SMAs can greatly alleviate the intermolecular aggregation and alter the molecular orientation from bimodal edge-on/face-on to predominant face-on while maintaining the compact molecular packing.As a result,a more favorable morphology with smaller domain sizes is formed for the MD1T-based blend films,which greatly improves the charge generation and charge transport for the corresponding PSCs.The best-performing MD1T-based device affords an efficiency of 12.43%,over seven times higher than that of the MD2T-based device.This work reveals the importance of the spacing between the neighboring side-chains in modulating the molecular aggregation and active layer morphology,and the obtained structure-performance relationships shall provide important guidance for designing highly efficient SMAs.

Design,methodology,and baseline of whole city‑million scale children and adolescents myopia survey(CAMS)in Wenzhou,China

Background:Myopia is the most common visual impairment in children and adolescents worldwide.This study described an economical and effective population-based screening pipeline and performed the project of a million scale children and adolescents myopia survey(CAMS),which will shed light on the further study of myopia from the level of epidemiology and precision medicine.Methods:We developed a novel population-based screening pattern,an intelligent screening process and internetbased information transmission and analysis system to carry out the survey consisting of school children in Wenzhou,China.The examination items include unaided distance visual acuity,presenting distance visual acuity,and noncycloplegic autorefraction.Myopia and high myopia were defined as spherical equivalent(SE)≤−1.00 diopters(D)and SE≤−6.00 D,respectively.Next,the reports of the vision checking were automatically sent to parents and the related departments.The CAMS project will be done two to four times annually with the support of the government.An online eyesight status information management system(OESIMS)was developed to construct comprehensive and efficient electronic vision health records(EVHRs)for myopia information inquiry,risk pre-warning,and further study.Results:The CAMS completed the first-round of screening within 30 days for 99.41%of Wenzhou students from districts and counties,in June 2019.A total of 1,060,925 participants were eligible for CAMS and 1,054,251(99.37%participation rate)were selected through data quality control,which comprised 1305 schools,and 580,609,251,050 and 170,967 elementary,middle,and high school students.The mean age of participants was 12.21±3.32 years(6-20 years),the female-to-male ratio was 0.82.The prevalence of myopia in elementary,middle,and high school students was 38.16%,77.52%,and 84.00%,respectively,and the high myopia incidence was 0.95%,6.90%,and 12.98%.Conclusions:The CAMS standardized myopia screening model involves automating large-scale information collection,data transmission,data analysis and early warning,thereby supporting myopia prevention and control.The entire survey reduced 90%of staff,cost,and time consumption compared with previous surveys.This will provide new insights for decision support for public health intervention.

Solution-derived poly（ethylene glycol）-TiOx nanocom- posite film as a universal cathode buffer layer for enhancing efficiency and stability of polymer solar cells

高度有效、稳定的聚合物太阳能电池( PSC )被 poly 采用导出答案的混血儿制作了(乙烯乙二醇)钛氧化物( PEG-TiO <潜水艇class=“ a-plus-plus ”>一篇小说和通用阴极缓冲层( CBL )的 x ) nanocomposite 电影，它罐头极大地由减少接口精力障碍并且提高费用抽取/收集改进设备性能。有改变的体积异质接面(BHJ ) 的转换 PSC 的性能基于这混合 nanocomposite CBL 被发现比有纯 TiO 的控制设备的那些好一些 < 潜水艇 class= “ a-plus-plus ” > x CBL 或没有 CBL。在 AM 1.5G 照耀下面的优秀力量变换效率直到 9.05%(100 mW 污獹獩 ? 潭敬畣慬? 楳癥? 慣慴祬楳?愠摮瀠潨潴慣慴祬楳？

铝离子电池中过渡金属硫族化合物正极材料

作为铝离子电池(AIBs)的正极材料,过渡金属硫族化合物(MX_(2)(X=S、Se、Te))具有理论比容量较高和电负性较低等优点,在铝离子电池应用领域极具发展前景。本文以提高过渡金属硫族化合物的储铝性能为目的,综述了过渡金属硫族化合物(MX_(2)(X=S、Se、Te))的储铝机理及其电化学性能的关系,并针对目前过渡金属硫族化合物存在的问题,总结研究者们提出的相应解决方案并归纳此类材料的主要改性技术手段。最后,对过渡金属硫族化合物正极材料的发展方向进行展望,并探讨改善其整体电化学性能的可行策略。