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A learning framework based on weighted knowledge transfer for holiday load forecasting

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Journal of Modern Power Systems and Clean Energy 2019年第2期7卷 329-339页

作者： pan zeng Chang SHENG Min JIN College of Computer Science and Electronic Engineering Hunan University

Since the variation pattern of load during holidays is different than that of non-holidays, forecasting holiday load is a challenging task. With a focus on this problem, we propose a learning framework based on weighted knowledge transfer for daily peak load forecasting during ***,we select source cities which can provide extra hidden knowledge to improve the forecast accuracy of the load of the target city. Then, all the instances which are from source cities and the target city will be weighted and trained by the improved weighted transfer learning algorithm which is based on the TrAdaBoost algorithm and can decrease negative transfer. We evaluate our method with the classical support vector machine method and a method based on knowledge transfer on a real data set, which includes eleven cities in Guangdong province of China,to illustrate the performance of the method. To solve the problem of limited historical holiday load data, we transfer the data from nearby cities based on the fact that nearby cities in Guangdong province of China have a similar economic development level and similar load variation pattern. The results of comparative experiments show that the framework proposed by this paper outperforms these methods in terms of mean absolute percent error and mean absolute scaled error.

关键词： Load forecasting Holiday effect Sparse data Weighted knowledge transfer

Investigation of processing–microstructure–property relationship using hot compression of a cone-shaped specimen

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Journal of Iron and Steel Research International 2020年第8期27卷 922-932页

作者： Wan-hui Huang pan zeng Li-ping Lei Department of Mechanical Engineering Tsinghua UniversityBeijing 100084China

Gradient microstructure of the specimen was achieved by applying gradient thermoplastic deformation via electric resist-ance heating and hot compression of the cone-shaped specimen. A numerical modeling and experiment tests are conducted to investigate the microstructure evolution and mechanical properties in different regions of the specimen subjected to the gradient process parameters. Microstructure analysis revealed a direct relationship between the grain size and processing parameters. The temperature distribution on the gradient specimen ranges from about 800 to 1110 ℃ and equivalent strain along the axis of symmetry of the specimen section ranges from about 0.1 to 1.2. Under a temperature of 1050 ℃ and the equivalent strain of 0.7, the middle region of the specimen section has fine and equiaxed prior-austenitic grains with an average size of (27?±?11) μm. Corresponding to the processing parameters, the lath martensite variants microstructure in this position with the highest hardness of (946?±?17) HV. Consequently, the linkages among hot compression parameters, microstructure, and material properties of hardness are established via a high-throughput method in a cone-shaped specimen.

关键词： Gradient deformation Hot forging High-throughput Numerical simulation Microstructure Hardness

Optimization of Cross-sectional Shapes of the Bi-2223/Ag Wires before Flat Rolling

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Chinese Journal of Mechanical Engineering 2009年第6期22卷 890-895页

作者： LU Yongjin zeng pan LEI Liping SUN Jianfeng Department of Mechanical Engineering Tsinghua University Beijing 100084 China Key Laboratory for Advanced Materials Processing Technology of Ministry of Education Tsinghua University Beijing 100084 China Innova Superconductor Technology Co. Ltd. Beijing 100176 China

Rolling process plays an important role in the manufacture of Bi-based high temperature superconductor tapes, and the plastic flow regularities of the superconducting wires during deformation will directly affect the ultimate quality of the tapes. In order to investigate the effect of cross-sectional shapes before fiat rolling on the performance and homogeneity of the tapes, some numerical models of Bi-2223/Ag wires with different cross-sectional shapes including circular, square, elliptical and racetrack cross-sections are constructed during the rolling process. By comparing the relative density, logarithmic strain ratio and length-width ratio on the filaments, it is revealed that Bi-2223/Ag wire with special-shaped cross-section can achieve better conductivity than the round wire, in particular, the racetrack cross-sectional wire has the second best performance among four wires. Based on material processability and experimental condition, tri-pass racetrack drawing technique is employed to optimize the process and obtain racetrack cross-sectional wire. The rolling process of Bi-2223/Ag wire with racetrack cross-section causes more intensive deformation of filaments in the center of the tape and achieves the filaments with larger length-width ratio. Also, the deformation distribution of filaments verifies the numerical results. Consequently, the racetrack drawing technique can be utilized for a reference during the mechanical processing and to increase the current transmission capacities of Bi-2223/Ag tapes.

关键词： rolling cross-sectional shape filament modelling

NUMERICAL SIMULATION OF MECHANICAL BEHAVIORS OF SUPERCONDUCTING POWDER BSCCO (BiSrCaCuO)

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Chinese Journal of Mechanical Engineering 2007年第3期20卷 59-61页

作者： ZHAO Yinghong LEI Liping zeng pan Key Laboratory for Advanced Materials Processing Technology of Ministry of Education Beijing 100084 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China

An equivalent continuum method and a deformable discrete method to describe the mechanical behaviors of superconducting powder BSCCO （BiSrCaCuO） aggregate are studied syste-matically. The equivalent continuum model idealizes the aggregation of the powder as an equivalent continuum material. The powder aggregate yielding is caused by not only the deviatoric stress but also the hydrostatic stress and the modified Drucker-Prager/Cap model is adopted to describe the mechanical behaviors of BSCCO powder aggregate in continuum method. The deformable discrete model is known as a direct model, which considers the discrete nature of the powder particles. Its framework encompasses the local behaviors between the particles, such as particles contact, sliding and rolling. Based on commercial finite element software ABAQUS, the equivalent continuum model and the deformable discrete model are used to simulate the confined compression of superconducting powder BSCCO, and the numerical results show agreement with experimental results, which verify the correctness of these built models. Compared with the equivalent continuum model based on macroscopic statistics method, the deformable discrete model can present the microscopic information during processing and can describe the nature of mechanical behaviors of superconducting powder BSCCO. But from an industrial viewpoint, the equivalent continuum model has a definitive edge over the microscopic models in that the gross behavior of the powder mass can be modeled and simulated on an industrial scale.

关键词： BSCCO(BiSrCaCuO) Mechanical behaviour Discrete method Continuum method

Local equivalent welding element to predict the welding deformations of plate-type structures

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Science China(Technological Sciences) 2008年第9期51卷 1502-1506页

作者： zeng pan GAO Yi LEI LiPing Department of Mechanical Engineering Tsinghua UniversityKey Laboratory for Advanced Materials Processing TechnologyMinistry of Education of ChinaBeijing 100084China

Considering the Heat Affected Zone (HAZ) of welding joint, the residual strain be-haviors of material under constraint and temperature circulation, as well as the activating mechanism of welding process, this paper addresses a new type welding element for numerical simulation of welding deformation, which is called the LEWE (the local equivalent welding element). This element can describe the basic char-acteristics of welded seam: the local position points of inherent strain, the equiva-lent size, the bending radius (or bending angle) from inherent strain, etc. It could be used to predict the welding deformation of plate-type structure. The comparisons between the computed deflection of welded plate and its experiment measurement are present. The results showed that the LEWE possesses a potential to simulate the deformation of welding process high-efficiently and precisely.

关键词： welding deformation local equivalency welding element

INFLUENCE OF ROLL DIAMETERS ON DEFORMATION BEHAVIOUR OF HIGH TEMPERATURE SUPERCONDUCTING TAPE

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Chinese Journal of Mechanical Engineering 2007年第4期20卷 75-78页

作者： LEI Liping ZHAO Yinghong zeng pan Key Laboratory for Advanced Materials Processing Technology Beijing 100084 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China

During plastic process, the material flow is strongly influenced by the contact area between deformed workpiece and die. In rolling process, difference of roll diameter makes the contact area between roll and deformed tape different, which leads to different material flow and the distribution of powder density. A numerical modelling of the first rolling process for 61-filament high temperature superconducting tape is constructed and the influences of roll diameters on deformation behavior of the tape are discussed. It can be found that the BiSrCaCuO （BSCCO） powder in the center of the tape has higher relative density than those in the periphery of the tape during rolling process. With the increase of roll diameter, the length of the contact arc in the roll gap expands which lead to the increasing of transversal strain and the decreasing of the related longitudinal strain. It makes the value of longitudinal strain ratio decrease gradually, which decreases the possibility of occurrence of the transversal shear band, simultaneously it increases the risk of occurrence of longitudinal crack.

关键词： Roll diameter Rolling process Filament Relative density

Robust lossless data hiding scheme

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Journal of Zhejiang University-Science C(Computers and Electronics) 2010年第2期11卷 101-110页

作者： Xian-ting zeng Xue-zeng pan Ling-di PING Zhuo LI School of Computer Science and Technology Zhejiang University Hangzhou 310027 China College of Information Engineering China Jiliang University Hangzhou 310018 China

This paper presents a robust lossless data hiding scheme. The original cover image can be recovered without any distortion after data extraction if the stego-image remains intact, and conversely, the hidden data can still be extracted correctly if the stego-image goes through JPEG compression to some extent. A cover image is divided into a number of non-overlapping blocks, and the arithmetic difference of each block is calculated. By shifting the arithmetic difference value, we can embed bits into the blocks. The shift quantity and shifting rule are fixed for all blocks, and reversibility is achieved. Furthermore, because the bit-0- and bit-1-zones are separated and the particularity of the arithmetic differences, minor changes applied to the stego-image generated by non-malicious attacks such as JPEG compression will not cause the bit-0- and bit-l-zones to overlap, and robustness is achieved. The new embedding mechanism can enhance embedding capacity and the addition of a threshold can make the al- gorithm more robust. Experimental results showed that, compared with previous schemes, the performance of the proposed scheme is significantly improved.

关键词： Watermarking Lossless data hiding Reversible data hiding Robust lossless data hiding Semi-fragile authentication

Achieving structurally stable O3-type layered oxide cathodes through site-specific cation-anion co-substitution for sodium-ion batteries

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Journal of Energy Chemistry 2024年第6期93卷 411-418,I0011页

作者： Yihao Shen Chen Cheng Xiao Xia Lei Wang Xi Zhou pan zeng Jianrong zeng Liang Zhang Institute of Functional Nano&Soft Materials(FUNSOM) Soochow UniversitySuzhou 215123JiangsuChina Institute for Advanced Study School of Mechanical EngineeringChengdu UniversityChengdu 610106SichuanChina Shanghai Synchrotron Radiation Facility Shanghai Advanced Research InstituteChinese Academy of SciencesShanghai 201204China Shanghai Institute of Applied Physics Chinese Academy of SciencesShanghai 201800China Jiangsu Key Laboratory of Advanced Negative Carbon Technologies Soochow UniversitySuzhou 215123JiangsuChina

O3-type layered oxides have garnered great attention as cathode materials for sodium-ion batteries because of their abundant reserves and high theoretical ***,challenges persist in the form of uncontrollable phase transitions and intricate Na^(+)diffusion pathways during cycling,resulting in compromised structural stability and reduced capacity over *** study introduces a special approach employing site-specific Ca/F co-substitution within the layered structure of O_(3)-NaNi_(0.5)Mn_(0.5)O_(2) to effectively address these ***,the strategically site-specific doping of Ca into Na sites and F into O sites not only expands the Na^(+)diffusion pathways but also orchestrates a mild phase transition by suppressing the Na^(+)/vacancy ordering and providing strong metal-oxygen bonding strength,*** as-synthesized Na_(0.95)Ca_(0.05)Ni_(0.5)Mn_(0.5)O_(1.95)F_(0.05)(NNMO-CaF)exhibits a mild O3→O3+O'3→P3 phase transition with minimized interlayer distance variation,leading to enhanced structural integrity and stability over extended *** a result,NNMO-CaF delivers a high specific capacity of 119.5 mA h g^(-1)at a current density of 120 mA g^(-1)with a capacity retention of 87.1%after 100 *** study presents a promising strategy to mitigate the challenges posed by multiple phase transitions and augment Na^(+)diffusion kinetics,thus paving the way for high-performance layered cathode materials in sodium-ion batteries.

关键词： Sodium-ion batteries O3-type layered oxides Site-specific co-doping Phase transition

Structural transition and magnetic properties of evaporated Fe/Gd multilayers

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Rare Metals 2008年第5期27卷 484-489页

作者： YANG Peiyong SONG Cheng zeng Fei pan Feng Laboratory of Advanced Materials Department of Materials Science and Engineering Tsinghua University Beijing 100084 China

Fe/Gd multilayers were prepared by alternate vapor deposition of pure Fe and Gd at a rate of 0.01-0.03 nm/s in an ultra-high-vacuum elec- tron-gun evaporation system. The effects of the constituent metal layer thickness on the microstructures and magnetic properties of the films were investigated by low angle X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer. The experimental results show that a transition from the polycrystalline to amorphous state in the Fe layers occurs with the decrease of Fe layer thickness in the Fe/Gd multilayers. The saturation magnetization of the multilayers reduces significantly with decreasing Fe layer thickness and increasing Gd layer thickness. A superparamagnetic behavior at room temperature is observed for the [Fe（0.6 nm）/Gd（4.0 nm）]15 multilayer due to the formation of discontinuous Fe layers.

关键词： multilayers amorphous state magnetization microstructure thin film