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Rational design of AgGaS/ZnS/ZnS quantum dots with a near-unity photoluminescence quantum yield via double shelling scheme

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Journal of Materials Science & Technology 2024年第2期169卷 235-242页

作者： H.X.Lu H.Liu Z.Z.Fu Y.Y.Chen H.Q.Dai Z.Hu W.L.Zhang R.Q.Guo institute for electric light sources School of Information Science and TechnologyFudan UniversityShanghai 200433China institute of Future lighting Academy for Engineering and TechnologyFudan UniversityShanghai 200433China Yiwu Research institute of Fudan University YiwuZhejiang 322000China Zhongshan-Fudan Joint Innovation Center Zhongshan 528437China

In this study,a two-step method was used to synthesize highly luminescent AgGaS/ZnS/ZnS quantum dots(QDs).In the first step,an inner ZnS shell was formed via a one-pot method,which resulted in a smaller lattice mismatch between the AgGaS core and the outer ZnS shell,thereby facilitating the formation of a thick outer shell.After the two-step shelling process,the synthesized AgGaS/ZnS/ZnS QDs showed an excellent photoluminescence quantum yield(PLQY)of 96.4%with a peak wavelength of 508 nm,repre-senting the highest PLQY reported thus far for AgGaS QDs.Furthermore,the effect of halogen ions in Zn precursors on the shelling process was investigated.It was proposed that the capacity of halogen ions to coordinate with the QDs influenced the balance between Zn cation diffusion and ZnS shelling reaction.Specifically,the ZnS shelling reaction was dominant when ZnCl_(2)was employed,while Zn cation diffusion was the dominant process under the I^(−)-rich environment.This work provides insights into the interfacial restructuring during the ZnS shelling and offers a clear map for the tailored synthesis of core/shell QDs.

关键词： AgGaS Quantum dots Photoluminescence Core/shell Alloyed core/shell interface

Finite Element Method for Transient electric Field by Using Indirect Laplace Transform with High Accuracy

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CSEE Journal of Power and Energy Systems 2024年第1期10卷 401-411页

作者： Teng Wen Xiang Cui Xuebao Li Sijia Liu Zhibin Zhao State Key Laboratory of Alternate electrical Power System with Renewable Energy sources North China Electric Power UniversityBeijing 102206China China electric Power Planning&Engineering institute Beijing 100120China

This paper focuses on the finite element method in the complex frequency domain(CFD-FEM)for the transient electric field.First,the initial value and boundary value problem of the transient electric field under the electroquasistatic field in the complex frequency domain is given.In addition,the finite element equation and the constrained electric field equation on the boundary are derived.Secondly,the indirect algorithm of the numerical inverse Laplace transform is introduced.Based on it,the calculation procedures of the CFD-FEM are illustrated in detail.Thirdly,the step response,zero-state response under the positive periodic square waveform(PPSW)voltage,and the zero-input response by the CFD-FEM with direct algorithm and indirect algorithm are compared.Finally,the reason for the numerical oscillations of the zero-state response under the PPSW voltage is analyzed,and the method to reduce oscillations is proposed.The results show that the numerical accuracy of the indirect algorithm of the CFD-FEM is more than an order of magnitude higher than that of the direct algorithm when calculating the step response of the transient electric field.The proposed method can significantly reduce the numerical oscillations of the zero-state response under the PPSW voltage.The proposed method is helpful for the calculation of the transient electric field,especially in the case of frequency-dependent parameters.

关键词： Electroquasistatic field transient electric field finite element method complex frequency domain numerical Laplace transform

Influence of Repetitive Impulse Waveforms on Surface Discharge Characteristics and Insulation Life for Polyimide Film

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CSEE Journal of Power and Energy Systems 2024年第2期10卷 746-755页

作者： Zhiyun Han Qingmin Li Yujin Guo Tao Liu Guojing Dong Hanwen Ren State Key Laboratory of Alternate electrical Power System with Renewable Energy sources North China Electric Power UniversityBeijing 102206China electric Power Research institute Beijing 100085China Inner Mongolia electric Economy and Technology Academy Hohhot 010020China

Accelerated insulation aging problems under high frequency repetitive impulses in power electronic transformers are drawing more and more attention in modern power systems. Partial discharge (PD) characteristics including discharge inception voltage, phase distribution and statistical characteristics on polyimide (PI) surface under different impulse waveforms and the insulation life of PI films are studied in this paper. We carry out experiments based on PD and insulation lifetime test systems, using five different types of repetitive impulses, including three bipolar waves and two unipolar waves. The experimental results show that there is little variation in discharge inception voltage under different waveforms, but great variation in phase distribution and statistical characteristics of PD. In addition, insulation life is approximately the same under different waveforms with the same polarity, and the aging rate under bipolar waveforms is larger than that under unipolar waveforms. We explain the differences between the bipolar and unipolar waveforms on insulation life, which can be concluded that the surface charge under unipolar waveform accumulates more significnatly compared with bipolar waveform and decreases the electric filed strength in discharging the air gap and inhibits surface discharge from occurring.

关键词： Insulation life polyimide film power electronic transformer repetitive impulse surface discharge characteristics

Harnessing data using symbolic regression methods for discovering novel paradigms in physics

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Science China(Physics,Mechanics & Astronomy) 2024年第6期67卷 1-11页

作者： Jianyang Guo Wan-Jian Yin College of Energy Soochow Institute for Energy and Materials Innovations(SIEMIS)Jiangsu Provincial Key Laboratory for Advanced Carbon Materials and Wearable Energy TechnologiesSoochow UniversitySuzhou 215006China Shanghai Qi Zhi institute Shanghai 200232China light Industry institute of Electrochemical Power sources Soochow UniversitySuzhou 215006China

In recent years,machine-learning methods have profoundly impacted research in the interdisciplinary fields of physics.However,most machine-learning models lack interpretability,and physicists doubt the credibility of their conclusions because they cannot be combined with prior physical knowledge.Therefore,this review focuses on symbolic regression,which is an interpretable machine-learning method.First,the relevant concepts of machine learning are introduced in conjunction with induction.Next,we provide an overview of symbolic regression methods.Subsequently,the recent directions for the application of symbolic regression methods in different subfields of physics are outlined,and an overview of the ways in which the applications of symbolic regression have evolved in the realm of physics is provided.The major aim of this review is to introduce the basic principles of symbolic regression and explain its applications in the field of physics.

关键词： machine learning genetic programming symbolic regression

Dynamically lithium-compensated polymer artificial SEI to assist highly stable lithium-rich manganese-based anode-free lithium metal batteries

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Rare Metals 2024年第6期43卷 2527-2535页

作者： Ming-Ji Peng Jin-Qiu Zhou Ting-Ting Han Yang Zhou Jie Liu Na Xu Zhen-Kang Wang Wen-Bin Lin Cheng-Lin Yan Key Laboratory of Core Technology of High Specific Energy Battery and Key Materials for Petroleum and Chemical Industry College of EnergySoochow University light Industry institute of Electrochemical Power sources School of Chemistry and Chemical Engineering Nantong University State Key Laboratory of Space Power-sources Technology Shanghai Institute of Space Power-Sources Centre énergie Matériaux et TélécommunicationsInstitut National de la Recherche Scientifique Zhangjiagang Industrial Technologies Soochow University

Owing to the unique structure,anode-free lithium metal batteries（AFLMBs） have higher energy density and lower production cost than traditional lithium metal batteries（LMBs） or lithium-ion batteries（LIBs）,However,AFLMBs suffer from an inherently finite Li reservoir and exhibit poor cycle stability,low Coulombic efficiency（CE） and severe dendrite growth.In this work,polydiallyl lithium disulfide（PDS-Li） was successfully synthesized and coated on Cu current collector by electrochemical polymerization.The PDS-Li acts as an additional lithium resource to compensate for the irreversible loss of lithium during cycling.In addition,the special structure and lithiophilicity of PDS-Li contribute to lower nucleation overpotential and uniform lithium deposition.When coupled with Li-rich manganese-based（LRM）cathode of Li1.2Mn0.54Ni0.13Co0.13O2,the anode-free full cell exhibits significantly improved cycle stability over 100 cycles and capacity retention of 63.3% and 57% after 80 and 100 cycles,respectively.We believe that PDS-Li can be used to ensure stable cycling performance and high-energy-density in AFLMBs.

关键词： Anode-free Artificial solid electrolyte interphase (SEI) Lithium metal batteries Lithium-rich cathode Finite element simulation

Micro-mechanism Study on the Different Antioxidants Protective Effect of Vegetable Oil by ReaxFF Molecular Dynamics

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CSEE Journal of Power and Energy Systems 2024年第3期10卷 1269-1279页

作者： Haoxi Cong Xuefeng Hu Hao Pan Qingmin Li State Key Laboratory of Alternate electrical Power System With Renewable Energy sources North China Electric Power UniversityBeijing 102206China

The aging problem of vegetable oil has severely restricted the popularization and application of vegetable oil transformers.Adding antioxidants is the most recommended solution.At present,there is insufficient research on the micromechanism application of the protective effect of antioxidants on vegetable oil.In this paper,multiple vegetable oil models with different types and concentrations of antioxidants are established.Then the molecular dynamics simulation based on ReaxFF is carried out at different temperatures and oxygen content.Results show that the protective mechanism of antioxidants is to release H and combine this with free radicals generated by the decomposition of unsaturated fatty acids(UFA)in the oil.In addition,the protective effects of four antioxidants show different results.The stronger ones are tert-butyl hydroquinone(TBHQ)and butylated hydroxytoluene(BHT),while the weaker ones are butylated hydroxyanisole(BHA)and propyl gallate(PG).TBHQ has a better protective effect at lower concentrations,but the decomposition of UFA is promoted at higher concentrations.When the temperature rises,the decomposition of UFA is promoted.With the addition of oxygen,smaller molecular compounds are easily oxidized,and the decomposition of UFA is accelerated.The above research could reveal the microscopic mechanism of antioxidant protection on vegetable oil,providing theoretical references for further exploration of effective vegetable oil aging protection technology.

关键词： Antioxidant molecular dynamics transformer vegetable oil

Framework for Preventive Control of Power Systems to Defend Against Extreme Events

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CSEE Journal of Power and Energy Systems 2024年第2期10卷 856-870页

作者： Yuwei Xiang Tong Wang Zengping Wang State Key Laboratory of Alternate electrical Power System with Renewable Energy sources North China Electric Power UniversityBeijing 102206China

Enhancing power system resilience against extreme events is becoming increasingly critical. This paper discusses a unified framework for preventive control of power systems to enhance system resilience, which includes three parts: resilience assessment, resilience grading, and resilience enhancement. First, the resilience assessment contains facility-level and system-level resilience assessment. The concept of fragility curve is used in the facility-level resilience assessment. Various resilience indices are developed in system-level resilience assessment to roundly depict the impacts of extreme events on power systems and determine the system resilience. On this basis, the resilience is divided into different levels by resilience grading strategy, which can efficiently quantify the severity of the impact of extreme events and provide decision-making for the resilience enhancement strategies. Then, control strategies for enhancing power system resilience are also divided according to different resilience levels. A controlled islanding based preventive control is proposed to enhance system resilience, which aims to strengthen the first defensive line of power systems to deal with extreme events. Finally, taking the typhoon disaster in extreme events as an example, two tests carried out with two typhoons demonstrate the efficiency of the proposed method.

关键词： Controlled islanding extreme events power system resilience preventive control

A spatiotemporal evolution model of a short-circuit arc to a secondary arc based on the improved charge simulation method

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Plasma Science and Technology 2024年第1期26卷 62-73页

作者：丛浩熹王宇轩乔力盼苏文晶李庆民 State Key Laboratory of Alternate electrical Power System with Renewable Energy sources North China Electric Power UniversityBeijing 102206People’s Republic of China

The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.

关键词： short-circuit arc secondary arc stochasticity improved charge simulation method arc time

Metal-free Optical Pressure Sensor with High Sensitivity and Extensive Range

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CSEE Journal of Power and Energy Systems 2024年第3期10卷 1291-1300页

作者： Mao Ji Meng Huang Haomin Lyu Sheng Shi Bo Qi Chengrong Li State Key Laboratory of Alternate electrical Power System with Renewable Energy sources North China Electric Power UniversityBeijing 102206China IEEE CSEE

Pressure monitoring of a transformer oil tank can grasp the pressure change process caused by gas production when severe internal defects occur and take timely measures to ensure the safe operation of the transformer.Existing pressure sensors generally use metal encapsulation or have an air cavity structure,threatening the transformer’s insulation if it is directly used inside the transformer.To this end,this paper proposes a method for developing a high-sensitivity,large-range,and metallizationfree optical pressure sensing device with temperature compensation.Fiber grating is encapsulated by fluorosilicone rubber and supplemented by an epoxy resin shielding shell on the outside.At the same time,a double-grating vertical arrangement is adopted to improve pressure measurement sensitivity,further avoiding the influence of temperature rise caused by a defect of the transformer on the measurement result of the sensor.In addition,by optimizing the geometric structure of the internal sensitizing element,pre-stretching length of the fiber grating,gap distance,and other parameters,probe size can be reduced while ensuring the sensor’s performance.Results show the proposed method can meet the requirements of sensor fabrication with different sensitivities and ranges,and to a certain extent,both high sensitivity and extensive ranges can be taken into account.The sensitivity of the fabricated prototype is 15 pm/kPa,and the range is about 0.2 MPa.At the same time,the metal-free feature of the sensor makes it suitable for use in various oil-immersed power equipment.It records oil pressure changes caused by oil discharge breakdown,making it sensitive to small pressure changes in early failures.

关键词： Highly sensitive extensive range optical sensing no metallization pressure perception temperature compensation transformer