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Research on Pulsar Time Steered Atomic Time Algorithm Based on DPLL

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Research in Astronomy and Astrophysics 2024年第3期24卷 237-248页

作者： Ze-Hao Zheng Yang Liu Dan Shen Fan Feng Jiu-Long Liu Yue-Xin Ma Xiang-Wei Zhu school of Electronic and Communication engineering Sun Yat-sen UniversityShenzhen 518107China school of Aeronautics and Astronautics Sun Yat-sen UniversityShenzhen 518107China school of Systems science and engineering Sun Yat-sen UniversityGuangzhou 510275China

In today’s society,there is a wide demand for high-precision and high-stability time service in the fields of electric power,communication,transportation and finance.At present,the time standard in various countries is mainly based on atomic clocks,but the frequency drift of atomic clocks will affect the long-term stability performance.Compared with atomic clocks,millisecond pulsars have better long-term stability and can complement with the excellent short-term stability of atomic clocks.In order to improve the long-term stability of the atomic timescale,and then improve the timing accuracy,this paper proposes an algorithm for steering the atomic clock ensemble(ACE)by ensemble pulsar time(EPT)based on digital phase locked loop(DPLL).First,the ACE and EPT are generated by the ALGOS algorithm,then the ACE is steered by EPT based on DPLL to calibrate the long-term frequency drift of the atomic clock,so that the generated steered atomic time follows both the short-term stability characteristics of ACE and the long-term stability characteristics of EPT,and finally,the steered atomic time is used to calibrate the local cesium clock.The experimental results show that the long-term stability of atomic time after steering is improved by 2 orders of magnitude compared with that before steering,and the daily drift of a local cesium clock after calibration is less than 9.47 ns in 3 yr,3 orders of magnitude higher than that before calibration on accuracy.

关键词： (stars) pulsars general-time-methods data analysis-instabilities

Self-templating synthesis of biomass-based porous carbon nanotubes for energy storage and catalytic degradation applications

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Green Energy & Environment 2024年第3期9卷 584-595页

作者： Manman Xu Shiqi Fu Yukai Wen Wei Li Qiongfang Zhuo Haida Zhu Zhikeng Zheng Yuwen Chen Anqi Wang Kai Yan Research Centre for Eco-environmental engineering School of Environment and Civil EngineeringDongguan University of TechnologyDongguan523808China school of environmental science and engineering Sun Yat-sen UniversityGuangzhou510275China

Dwindling energy sources and a worsening environment are huge global problems,and biomass wastes are an under-exploited source of material for both energy and material generation.Herein,self-template decoction dregs of Ganoderma lucidum-derived porous carbon nanotubes(ST-DDLGCs)were synthesized via a facile and scalable strategy in response to these challenges.ST-DDLGCs exhibited a large surface area(1731.51 m^(2)g^(-1))and high pore volume(0.76 cm^(3)g^(-1)),due to the interlacing tubular structures of precursors and extra-hierarchical porous structures on tube walls.In the ST-DDLGC/PMS system,the degradation efficiency of capecitabine(CAP)reached~97.3%within 120 min.Moreover,ST-DDLGCs displayed high catalytic activity over a wide pH range of 3–9,and strong anti-interference to these typical and ubiquitous anions in wastewater and natural water bodies(i.e.,H_(2)PO_(4)^(-),NO_(3)^(-),Cl^(-) and HCO_(3)^(-)),in which a ^(1)O_(2)-dominated oxidation was identified and non-radical mechanisms were deduced.Additionally,ST-DDLGC-based coin-type symmetrical supercapacitors exhibited outstanding electrochemical performance,with specific capacitances of up to 328.1 F g^(-1)at 0.5 A g^(-1),and cycling stability of up to 98.6%after 10,000 cycles at a current density of 2 A g^(-1).The superior properties of ST-DDLGCs could be attributed to the unique porous tubular structure,which facilitated mass transfer and presented numerous active sites.The results highlight ST-DDLGCs as a potential candidate for constructing inexpensive and advanced environmentally functional materials and energy storage devices.

关键词： Ganoderma lucidum residue Porous carbon nanotubes Self-template method Wastewater treatment Supercapacitor electrode

Carbon-coated hybrid crystals with fast electrochemical reaction kinetics for ultra-stable and high-load sodium-ion batteries

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Rare Metals 2024年第2期43卷 647-657页

作者： Chuan Ou Ming-Dong Tan Zhen-Bang Li Zhao-Jie Li Fei Tian Zheng-Ping Qiao Dan-Ni Lei Cheng-Xin Wang State Key Laboratory of Optoelectronic Materials and Technologies School of Materials Science and EngineeringSun Yat-Sen UniversityGuangzhou510275China

Owing to its high theoretical capacity and low cost,Sn has attracted significant attention in sodium-ion batteries.However,the slow kinetics of electrochemical reactions and the rapid decay of capacity resulting from drastic changes in the volume of Sn,as well as persistent side reactions between Sn and the organic electrolyte during the(de)sodium process,have limited its commercialization.To improve the electrochemical performance of Sn-based materials,the bottom-up method is normally used to prepare carbon-coated nanoparticles.However,its complex preparation processes and harsh conditions make it unsuitable for practical applications.Herein,a carbon-coated hybrid crystal composite(Sn/SnO_(x)@C)was prepared using an up-bottom method with commercial Sn/SnO nanoparticles.Various effects accelerate the electrochemical kinetics and inhibit the coarsening of Sn crystals.The Sn/SnO_(x)@C composite electrode exhibited capacity retention of 80.7%even after approximately 1000 cycles(360.4 mAh·g^(−1)) at a current density of 1 A·g^(−1).The high-load Na_(3)V_(2)(PO4)3||Sn/SnO_(x)@C full cell presents a capacity retention rate of 91.7%after 150 cycles at the current density of 0.5 A·g^(−1).This work may significantly accelerate the commercialization of the Sn/SnO_(x)@C composite in sodium-ion batteries with high energy density.

关键词： Sodium-ion batteries(SIBs) Sn-based anode Ultraviolet curing Up-bottom method

Securing Forwarding Layers from Eavesdropping Attacks Using Proactive Approaches

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Computers, Materials & Continua 2024年第4期79卷 563-580页

作者： Jiajun Yan Ying Zhou Anchen Dai Tao Wang school of Electronics and Communication engineering Sun Yat-sen UniversityShenzhen518107China

As an emerging network paradigm,the software-defined network(SDN)finds extensive application in areas such as smart grids,the Internet of Things(IoT),and edge computing.The forwarding layer in software-defined networks is susceptible to eavesdropping attacks.Route hopping is amoving target defense(MTD)technology that is frequently employed to resist eavesdropping attacks.In the traditional route hopping technology,both request and reply packets use the same hopping path.If an eavesdropping attacker monitors the nodes along this path,the risk of 100%data leakage becomes substantial.In this paper,we present an effective route hopping approach,called two-day different path(TDP),that turns communication paths into untraceable moving targets.This technology minimizes the probability of data leakage by transmitting request data and reply data through different paths.Firstly,a brief introduction to the network model and attack model involved in this paper is given.Secondly,the algorithm and processingmethod of the TDP are proposed.Thirdly,the paper proposes three differentmetrics tomeasure the effectiveness of the proposed approach.Finally,theoretical analysis and simulation results show that the TDP can effectively reduce the percentage of data exposure,decrease eavesdropping attack success probability,and improve the unpredictability of the path.

关键词： Route hopping moving target defense software-defined network two-way different path metrics

A Composite Transformer-Based Multi-Stage Defect Detection Architecture for Sewer Pipes

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Computers, Materials & Continua 2024年第1期78卷 435-451页

作者： Zifeng Yu Xianfeng Li Lianpeng sun Jinjun Zhu Jianxin Lin school of Computer science and engineering Macao University of Science and TechnologyMacao999078China school of environmental science and engineering Sun Yat-sen UniversityGuangzhou510275China Guangdong AIKE environmental science and Technology Co. Ltd.Zhongshan528400China

Urban sewer pipes are a vital infrastructure in modern cities,and their defects must be detected in time to prevent potential malfunctioning.In recent years,to relieve the manual efforts by human experts,models based on deep learning have been introduced to automatically identify potential defects.However,these models are insufficient in terms of dataset complexity,model versatility and performance.Our work addresses these issues with amulti-stage defect detection architecture using a composite backbone Swin Transformer.Themodel based on this architecture is trained using a more comprehensive dataset containingmore classes of defects.By ablation studies on the modules of combined backbone Swin Transformer,multi-stage detector,test-time data augmentation and model fusion,it is revealed that they all contribute to the improvement of detection accuracy from different aspects.The model incorporating all these modules achieves the mean Average Precision(mAP)of 78.6% at an Intersection over Union(IoU)threshold of 0.5.This represents an improvement of 14.1% over the ResNet50 Faster Region-based Convolutional Neural Network(R-CNN)model and a 6.7% improvement over You Only Look Once version 6(YOLOv6)-large,the highest in the YOLO methods.In addition,for other defect detection models for sewer pipes,although direct comparison with themis infeasible due to the unavailability of their private datasets,our results are obtained from a more comprehensive dataset and have superior generalization capabilities.

关键词： Sewer pipe defect detection deep learning model optimization composite transformer

An improved algorithm for retrieving thin sea ice thickness in the Arctic Ocean from SMOS and SMAP L-band radiometer data

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Acta Oceanologica Sinica 2024年第3期43卷 127-138页

作者： Lian He senwen Huang Fengming Hui Xiao Cheng school of Geospatial engineering and science Sun Yat-Sen Universityand Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)Zhuhai 519082China Key Laboratory of Comprehensive Observation of Polar Environment(sun yat-sen university) Ministry of EducationZhuhai 519082China

The aim of this study was to develop an improved thin sea ice thickness(SIT)retrieval algorithm in the Arctic Ocean from the Soil Moisture Ocean Salinity and Soil Moisture Active Passive L-band radiometer data.This SIT retrieval algorithm was trained using the simulated SIT from the cumulative freezing degree days model during the freeze-up period over five carefully selected regions in the Beaufort,Chukchi,East Siberian,Laptev and Kara seas and utilized the microwave polarization ratio(PR)at incidence angle of 40°.The improvements of the proposed retrieval algorithm include the correction for the sea ice concentration impact,reliable reference SIT data over different representative regions of the Arctic Ocean and the utilization of microwave polarization ratio that is independent of ice temperature.The relationship between the SIT and PR was found to be almost stable across the five selected regions.The SIT retrievals were then compared to other two existing algorithms(i.e.,UH_SIT from the university of Hamburg and UB_SIT from the university of Bremen)and validated against independent SIT data obtained from moored upward looking sonars(ULS)and airborne electromagnetic(EM)induction sensors.The results suggest that the proposed algorithm could achieve comparable accuracies to UH_SIT and UB_SIT with root mean square error(RMSE)being about 0.20 m when validating using ULS SIT data and outperformed the UH_SIT and UB_SIT with RMSE being about 0.21 m when validatng using EM SIT data.The proposed algorithm can be used for thin sea ice thickness(<1.0 m)estimation in the Arctic Ocean and requires less auxiliary data in the SIT retrieval procedure which makes its implementation more practical.

关键词： Arctic sea ice sea ice thickness remote sensing Soil Moisture Active Passive(SMAP) Soil Moisture Ocean Salinity and Soil(SMOS)

MIDNet:Deblurring Network for Material Microstructure Images

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Computers, Materials & Continua 2024年第4期79卷 1187-1204页

作者： Jiaxiang Wang Zhengyi Li Peng Shi Hongying Yu Dongbai sun National Center for Materials Service Safety University of Science and Technology BeijingBeijing100083China school of Materials Sun Yat-Sen UniversityShenzhen518107China school of Materials science and engineering Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)Sun Yat-Sen UniversityGuangzhou510006China

Scanning electron microscopy(SEM)is a crucial tool in the field of materials science,providing valuable insightsinto the microstructural characteristics of materials.Unfortunately,SEM images often suffer from blurrinesscaused by improper hardware calibration or imaging automation errors,which present challenges in analyzingand interpretingmaterial characteristics.Consequently,rectifying the blurring of these images assumes paramountsignificance to enable subsequent analysis.To address this issue,we introduce a Material Images DeblurringNetwork(MIDNet)built upon the foundation of the Nonlinear Activation Free Network(NAFNet).MIDNetis meticulously tailored to address the blurring in images capturing the microstructure of materials.The keycontributions include enhancing the NAFNet architecture for better feature extraction and representation,integratinga novel soft attention mechanism to uncover important correlations between encoder and decoder,andintroducing newmulti-loss functions to improve training effectiveness and overallmodel performance.We conducta comprehensive set of experiments utilizing the material blurry dataset and compare them to several state-of-theartdeblurring methods.The experimental results demonstrate the applicability and effectiveness of MIDNet in thedomain of deblurring material microstructure images,with a PSNR(Peak Signal-to-Noise Ratio)reaching 35.26 dBand an SSIM(Structural Similarity)of 0.946.Our dataset is available at:https://***/woshigui/MIDNet.

关键词： Image deblurring material microstructure attention mechanism deep learning

Why Are Arctic Sea Ice Concentration in September and Its Interannual Variability Well Predicted over the Barents–East Siberian Seas by CFSv2?

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Journal of Meteorological Research 2024年第1期38卷 53-68页

作者： Yifan XIE Ke FAN Hongqing YANG school of Atmospheric sciences Sun Yat-sen Universityand Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)Zhuhai 519082

To further understand the prediction skill for the interannual variability of the sea ice concentration(SIC)in specific regions of the Arctic,this paper evaluates the NCEP Climate Forecast System version 2(CFSv2),in predicting the autumn SIC and its interannual variability over the Barents–East Siberian Seas(BES).It is found that CFSv2 presents much better prediction skill for the September SIC over BES than the Arctic as a whole at 1–6-month leads,and high prediction skill for the interannual variability of the SIC over BES is displayed at 1–2-month leads after removing the linear trend.CFSv2 can reasonably reproduce the relationship between the SIC over BES in September and such factors as the surface air temperature(SAT),200-hPa geopotential height,sea surface temperature(SST),and North Atlantic Oscillation.In addition,it is found that the prescribed SIC initial condition in August as an input to CFSv2 is also essential.Therefore,the above atmospheric and oceanic factors,as well as an accurate initial condition of SIC,all contribute to a high prediction skill for SIC over BES in September.Based on a statistical prediction method,the contributions from individual predictability sources are further identified.The high prediction skill of CFSv2 for the interannual variability of SIC over BES is largely attributable to its accurate predictions of the SAT and SST,as well as a better initial condition of SIC.

关键词： sea ice concentration the Barents-East Siberian Seas Climate Forecast System version 2(CFSv2) prediction skill predictability source atmospheric and oceanic factors initial condition

Iodine enrichment in the groundwater in South China and its hydrogeochemical control

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Journal of environmental sciences 2024年第8期142卷 226-235页

作者： Fengping Zhou Qianting Xu Yuyun Chen Weihua Zhang Rongliang Qiu Guangdong Provincial Key Laboratory of environmental Pollution and Remediation Technology Guangdong Provincial Engineering Research Center for Heavy Metal Contaminated Soil RemediationSchool of Environmental Science and EngineeringSun Yat-sen UniversityGuangzhou 510275China Shenzhen Research Institute Sun Yat-sen UniversityShenzhen 518057China Guangdong Provincial Key Laboratory of Agricultural&Rural Pollution Abatement and environmental Safety School of Natural Resources and EnvironmentSouth China Agricultural UniversityGuangzhou 510642China Guangdong Laboratory for Lingnan Modern Agriculture Guangzhou 510642China

In North China,iodine-rich groundwater has been extensively studied,but few in South China.This study aimed to investigate the characteristics of iodine-rich groundwater in South China and identify potential contamination sources.The results revealed that the average concentration of iodine in groundwater was 890μg/L,with a maximumconcentration of 6350μg/L,exceeding the permitted levels recommended by the World Health Organization(5–300μg/L).Notably,the enrichment of iodide occurred in acidic conditions(pH=6.6)and a relatively low Eh environment(Eh=198.4 mV).Pearson correlation and cluster analyses suggested that the enrichment of iodide could be attributed to the intensified redox process involving Mn(II),iodine(I_(2)),or iodate(IO_(3)^(−))in the soil.The strong affinity between Mn(II)and I_(2)/IO_(3)^(−)facilitated their interaction,resulting in the formation and mobilization of I^(−)from the soil to the groundwater.Leaching experiments further confirmed that reducing substances(such as sodium sulfides,ascorbic acids,and fulvic acids)in the soil with low dissolved oxygen(DO)levels(3.8 mg/L)promoted the oxidation of I^(−)into I_(2)or IO_(3)^(−),leading to its stabilization.This research provides new insights into the characteristics and mechanisms of I^(−)enrichment in groundwater in South China,and emphasizes the significance of the redox reactions involving Mn(II)and I_(2)/IO_(3)^(−),as well as the influence of soil properties in regulating the occurrence and transportation of iodine species within groundwater systems.

关键词： Iodine enrichment Acid environment Groundwater South China Manganese