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Univariate Time Series Anomaly Detection Based on Hierarchical Attention Network

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Tsinghua Science and Technology 2024年第4期29卷 1181-1193页

作者： Zexi Chen Dongqiang Jia Yushu Sun Lin Yang wenjie Jin Ruoxi Liu State Grid Beijing Electric Power Company Beijing 100031China Institute of Electrical Engineering Chinese Academy of SciencesBeijing 100190China

In order to support the perception and defense of the operation risk of the medium and low voltage distribution system, it is crucial to conduct data mining on the time series generated by the system to learn anomalous patterns, and carry out accurate and timely anomaly detection for timely discovery of anomalous conditions and early alerting. And edge computing has been widely used in the processing of Internet of Things (IoT) data. The key challenge of univariate time series anomaly detection is how to model complex nonlinear time dependence. However, most of the previous works only model the short-term time dependence, without considering the periodic long-term time dependence. Therefore, we propose a new Hierarchical Attention Network (HAN), which introduces seven day-level attention networks to capture fine-grained short-term time dependence, and uses a week-level attention network to model the periodic long-term time dependence. Then we combine the day-level feature learned by day-level attention network and week-level feature learned by week-level attention network to obtain the high-level time feature, according to which we can calculate the anomaly probability and further detect the anomaly. Extensive experiments on a public anomaly detection dataset, and deployment in a real-world medium and low voltage distribution system show the superiority of our proposed framework over state-of-the-arts.

关键词： edge computing anomaly detection univariate time series self-attention

Investigation of Projectile Impact Behaviors of Graphene Aerogel Using Molecular Dynamics Simulations

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Computer Modeling in Engineering & Sciences 2024年第6期139卷 3047-3061页

作者： Xinyu Zhang wenjie Xia Yang Wang Liang Wang Xiaofeng Liu Department of Engineering Mechanics Shanghai Jiao Tong UniversityShanghai200240China Department of Aerospace Engineering Iowa State UniversityAmesIA50011USA School of Materials Science and Engineering University of Science&Technology BeijingBeijing100083China Zernike Institute for Advanced Materials University of GroningenGroningen9747The Netherlands

Graphene aerogel(GA),as a novel solid material,has shown great potential in engineering applications due to its unique mechanical *** this study,the mechanical performance of GA under high-velocity projectile impacts is thoroughly investigated using full-atomic molecular dynamics(MD)*** study results show that the porous structure and density are key factors determining the mechanical response of GA under impact ***,the impact-induced penetration of the projectile leads to the collapse of the pore structure,causing stretching and subsequent rupture of covalent bonds in graphene ***,the effects of temperature on the mechanical performance of GA have been proven to be minimal,thereby highlighting the mechanical stability of GA over a wide range of ***,the energy absorption density(EAD)and energy absorption efficiency(EAE)metrics are adopted to assess the energy absorption capacity of GA during projectile *** research findings of this work demonstrate the significant potential of GA for energy absorption applications.

关键词： Graphene aerogel molecular dynamics simulation impact response energy absorption

Structure and defect dual-engineering of cobalt oxides for lowtemperature Zn-air batteries

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Nano Research 2024年第5期17卷 4108-4117页

作者： Hang Lei Zhuowen Huangfu Liangjun Chen Xuelin Yang Zilong Wang wenjie Mai Hubei Provincial Collaborative Innovation Center for New Energy Microgrid College of Electrical Engineering&New EnergyChina Three Gorges UniversityYichang 443002China Siyuan Laboratory Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Energy MaterialsDepartment of PhysicsJinan UniversityGuangzhou 510632China

The exploration of bifunctional electrocatalysts with high catalytic activity and long-term durability for low-temperature Zn-air batteries(ZABs)is an ongoing ***,quintet-shelled hollow spheres,P-doped multi-layer Co_(3)O_(4)(PM-Co_(3)O_(4)),with enriched oxygen vacancies are prepared by thermally induced mass relocation and a simple phosphating *** advanced characterizations reveal P anion-induced effects on internal electronic structure and local coordination *** finite element method elucidates that the complex multi-layer spherical nanostructure is conducive to the transport and diffusion of OH-and O_(2).Benefiting from its unique structural features and abundant oxygen vacancies,the well-designed PM-Co_(3)O_(4) presents small reversible oxygen overpotential for catalyzing oxygen reduction/evolution ***,the fabricated low-temperature ZABs based on PM-Co_(3)O_(4) as air-cathode exhibit high power density(20.8 mW·cm^(-2))and long-term stability(over 600 cycles)at the ultra-low temperature of-40℃,outperforming state-of-art Pt/C+IrO_(2)-based ***,the dynamic evolution mechanism of cobalt oxide catalysts during ZAB operation is *** work provides a guideline to design efficient electrocatalysts with regulated electronic configurations and exquisite nano-/microstructures for ZABs under extreme working conditions.

关键词： Zn-air batteries electrocatalysts low temperature hollow spheres oxygen vacancies

RPUF用rGO/SiO2气凝胶阻燃涂层制备及性能研究

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中国安全科学学报 2020年第9期30卷 142-148页

作者：江赛华黄裕斌游文杰华南理工大学机械与汽车工程学院广东广州510641

为改善聚氨酯硬泡(RPUF)的易燃特性,提升其火灾安全性,采用溶胶-凝胶法将还原氧化石墨烯(rGO)与二氧化硅(SiO2)气凝胶结合制备出复合rGO/SiO2气凝胶,与聚二甲基硅氧烷(PDMS)复配后涂敷于RPUF表面,制备涂层阻燃RPUF;采用扫描电子显微镜(S... 详细信息

为改善聚氨酯硬泡(RPUF)的易燃特性,提升其火灾安全性,采用溶胶-凝胶法将还原氧化石墨烯(rGO)与二氧化硅(SiO2)气凝胶结合制备出复合rGO/SiO2气凝胶,与聚二甲基硅氧烷(PDMS)复配后涂敷于RPUF表面,制备涂层阻燃RPUF;采用扫描电子显微镜(SEM)和红外光谱分析rGO/SiO2气凝胶的形貌结构;通过热重和垂直燃烧测试研究涂层阻燃RPUF的热解行为和阻燃性能;探究不同rGO含量对阻燃性能的影响,揭示涂层阻燃机制。结果表明:气凝胶涂层高温下残炭率高,热稳定性优异,能够抵抗热量侵蚀;其中0.05%rGO/SiO2涂层阻燃RPUF到达V-0级别,表现出快速的自熄性能。气凝胶涂层可以作为高效物理屏障,阻断或延缓传质传热过程。

关键词：聚氨酯硬泡(RPUF) 还原氧化石墨烯(rGO)/二氧化硅(SiO2) 气凝胶阻燃涂层扫描电子显微镜(SEM) 物理屏障

High-performance Ti_(3)C_(2)T_(x)achieved by polyaniline intercalation and gelatinization as a high-energy cathode for zinc-ion capacitor

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Nano Research 2024年第6期17卷 5305-5316页

作者： Peng Liao ZiYu Geng Xin Zhang wenjie Yan Zenghui Qiu Haijun Xu College of Mathematics and Physics Beijing University of Chemical TechnologyBeijing 100029China

The actual manufacture of supercapacitors(SCs)is restricted by the inadequate energy density,and the energy density of devices can be properly promoted by assembling zinc-ion capacitors(ZICs)which used capacitive cathode and battery-type ***-dimensional(2D)MXene has brought great focuses in the electrode research on the foundation of large redox-active surface,but the specific capacitance is still affected by the tight stacking of ***_(3)C_(2)T_(x)@polyaniline(PANI)heterostructures are prepared by uniformly depositing the conductive polymer PANI nanorods as the intercalation agent into the external of Ti_(3)C_(2)T_(x)nanosheets to inhibit ***,by using graphene oxide(GO)-assisted low-temperature hydrothermal self-assembly manufacture,2D heterostructures are assembled into the three-dimensional(3D)porous crosslinked Ti_(3)C_(2)T_(x)@PANI-reduced graphene oxide(RGO)*** to the synergistic work of PANI nanorods,Ti_(3)C_(2)T_(X)nanosheets,and 3D crosslinking frameworks of RGO to match capacitive and battery effects,3D porous hierarchical Ti_(3)C_(2)T_(x)@PANI-RGO heterostructure hydrogels have rich ion transport channels,a large number of active sites,and excellent reaction *** is assembled by using Ti_(3)C_(2)T_(x)@PANI-RGO heterostructure hydrogels as cathodes and zinc foil as *** this work,Ti_(3)C_(2)T_(x)@PANI-RGO//Zn ZIC exhibits a wide working window(2.0 V),marked specific capacitance(589.89 F·g^(−1)at 0.5 A·g−1),salient energy density(327.71 Wh·kg^(−1)at 513.61 W·kg^(−1)and 192.20 Wh·kg^(−1)at 13,005.87 W·kg^(−1)),and durable cycling stability(97.87%capacitance retention after 10,000 cycles at 10 A·g^(−1)).This study emphasizes the device design of ZICs and the broad prospect of Ti_(3)C_(2)T_(x)-based hydrogels as viable cathodes for ZICs.

关键词： polyaniline(PANI) Ti_(3)C_(2)T_(x)@PANI heterostructure intercalation process three-dimensional(3D)porous hydrogel high energy density zinc-ion capacitor

Efficient elimination of carbamazepine using polyacrylonitrile-supported pyridine bridged iron phthalocyanine nanofibers by activating peroxymonosulfate in dark condition

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Journal of Environmental Sciences 2024年第3期137卷 224-236页

作者： Zhexin Zhu wenjie Qian Zhiguo Shang Xiaoji Ma Zhendong Wang Wangyang Lu Wenxing Chen National Engineering Lab for Textile Fiber Materials and Processing Technology(Zhejiang) Zhejiang Sci-Tech UniversityHangzhou 310018China

The monoaminotrinitro iron phthalocyanine(FeMATNPc)is used to connect with isonicotinic acid(INA)for amide bonding and axial coordination to synthetic a unique catalyst FeMATNPc-INA,which is loaded in polyacrylonitrile(PAN)nanofibers by *** introduction of INA destroys theπ-πconjugated stack structure in phthalocyanine molecules and exposes more active *** FeMATNPc-INA structure is characterized by X-ray photoelectron spectroscopy and UV-visible absorption spectrum,and the FeMATNPcINA/PAN structure is characterized by Fourier transform infrared spectroscopy and X-ray *** FeMATNPc-INA/PAN can effectively activate peroxymonosulfate(PMS)to eliminate carbamazepine(CBZ)within 40 minutes(PMS 1.5 mmol/L)in the *** effects of catalyst dosage,PMS concentration,pH and inorganic anion on the degradation of CBZ are *** has been confirmed by electron paramagnetic resonance,gas chromatography–mass spectroscopy and free radical capture experiments that the catalytic system is degraded by·OH,SO4^(·-)and Fe(IV)=O are the major active species,the singlet oxygen(^(1)O_(2))is the secondary active *** degradation process of CBZ is analyzed by ultra-high performance liquid chromatography-mass spectrometry and the aromatic compounds have been degraded to small molecular acids.

关键词： Pyridine bridged iron phthalocyanine Isonicotinic chloride hydrochloride Efficient elimination Peroxymonosulfate activation Degradation pathway

A data-driven model of drop size prediction based on artificial neural networks using small-scale data sets

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Chinese Journal of Chemical Engineering 2024年第2期66卷 71-83页

作者： Bo Wang Han Zhou Shan Jing Qiang Zheng wenjie Lan Shaowei Li Institute of Nuclear and New Energy Technology Tsinghua UniversityBeijing 100084China State Key Laboratory of Heavy Oil Processing China University of Petroleum(Beijing)Beijing 102249China State Key Laboratory of Chemical Engineering Tsinghua UniversityBeijing 100084China

An artificial neural network(ANN)method is introduced to predict drop size in two kinds of pulsed columns with small-scale data *** training,the deviation between calculate and experimental results are 3.8%and 9.3%,*** ANN model,the influence of interfacial tension and pulsation intensity on the droplet diameter has been *** size gradually increases with the increase of interfacial tension,and decreases with the increase of pulse *** can be seen that the accuracy of ANN model in predicting droplet size outside the training set range is reach the same level as the accuracy of correlation obtained based on experiments within this *** two kinds of columns,the drop size prediction deviations of ANN model are 9.6%and 18.5%and the deviations in correlations are 11%and 15%.

关键词： Artificial neural network Drop size Solvent extraction Pulsed column Two-phase flow Hydrodynamics

Effects of wind speed,underlying surface,and seed morphological traits on the secondary seed dispersal in the Tengger Desert,China

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Journal of Arid Land 2024年第4期16卷 531-549页

作者： QU wenjie ZHAO Wenzhi YANG Xinguo WANG Lei ZHANG Xue QU Jianjun Northwest Institute of Eco-Environment and Resources Chinese Academy of SciencesLanzhou 730000China Key Laboratory of Restoration and Reconstruction of Degraded Ecosystems in Northwestern China of Ministry of Education Ningxia UniversityYinchuan 750021China University of Chinese Academy of Sciences Beijing 100049China School of Ecology and Environment Ningxia UniversityYinchuan 750021China

The maintenance of sand-fixing vegetation is important for the stability of artificial sand-fixing systems in which seed dispersal plays a key *** on field wind tunnel experiments using 11 common plant species on the southeastern edge of the Tengger Desert,China,we studied the secondary seed dispersal in the fixed and semi-fixed sand dunes as well as in the mobile dunes in order to understand the limitations of vegetation regeneration and the maintenance of its *** results indicated that there were significant variations among the selected 11 plant species in the threshold of wind speed(TWS).The TWS of Caragana korshinskii was the highest among the 11 plant species,whereas that of Echinops gmelinii was the *** morphological traits and underlying surface could generally explain the *** the secondary seed dispersal processes,the proportions of seeds that did not disperse(no dispersal)and only dispersed over short distance(short-distance dispersal within the wind tunnel test section)were significantly higher than those of seeds that were buried(including lost seeds)and dispersed over long distance(long-distance dispersal beyond the wind tunnel test section).Compared with other habitats,the mobile dunes were the most difficult places for secondary seed *** seeds were the easiest to be found in the semi-fixed sand dunes,whereas fixed sand dunes were the best sites for seeds that dispersed over long *** results of linear mixed models showed that after controlling the dispersal distance,smaller and rounder seeds dispersed *** index and wind speed were the two significant influencing factors on the burial of *** explanatory power of wind speed,underlying surface,and seed morphological traits on the seeds that did not disperse and dispersed over short distance was far greater than that on the seeds that were buried and dispersed over long distance,implying that the processes and mechanisms of burial and lo

关键词： seed dispersal seed morphological traits wind speed vegetation regeneration wind tunnel Tengger Desert

Cobalt-doped TiO_(2)@C hierarchical nanocomposites derived from Ti_(3)C_(2) MXene as cathodes for hybrid magnesium-lithium batteries

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Nano Research 2024年第1期17卷 253-261页

作者： Xiaohui Li Yakun Tang Lang Liu Yue Zhang Yang Gao Mao Qian wenjie Ma State Key Laboratory of Chemistry and Utilization of Carbon Based Energy Resources College of ChemistryXinjiang UniversityUrumqi 830017China

TiO_(2)has been explored in hybrid magnesium-lithium batteries(HMLBs)due to the advantages of low self-discharge and small volume expansion during ion ***,how to improve the inherently low ionic and electrical conductivity of TiO_(2)is the problem that needs to be *** this work,a smart strategy is adopted to prepare cobalt-doped TiO_(2)@C(Co^(4+)-TiO_(2)@C)hierarchical nanocomposite derived from Co(II)(OH)n@*** with TiO_(2)@C(without cobalt doping),Co^(4+)-TiO_(2)@C shows the highest specific capacity(154.7 mAh·g^(-1)at 0.1 A·g^(-1)after 200 cycles)and extraordinary rate performance in *** excellent electrochemical performance of Co4+-TiO_(2)@C is ascribed to the synergistic effect of the hierarchical structure and *** experimental results and density functional theory(DFT)calculation reveal that the cobalt-doping has effectively improved the electronic conductivity and reduced the Li+migration *** work provides a new insight to design TiO_(2)-based cathode materials with high-performance in HMLBs.

关键词： Ti_(3)C_(2)MXene TiO_(2) hybrid magnesium-lithium batteries hierarchical structure cobalt-doping