AQUEOUS SYNTHESIS OF HIGH QUANTUM YIELD AND MONODISPERSED THIOL-CAPPED CdxZn1-xTe QUANTUM DOTS BASED ON ELECTROCHEMICAL METHOD

JUNWEI LI,YANG JIANG,YUGANG ZHANG,DI WU,ANQI LUO,ZHONGPING ZHANG 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2012 NANO Vol.7 No.2

A facile green approach has been developed to control the growth regime in the aqueous synthesis of CdxZn1-xTe semiconductor quantum dots (QDs) based on the electrochemistry method. The Low growth temperature and slow injection of Te precursor are used to prolong the diffusion controlled stage and thus suppress Ostwald ripening during the nanocrystal growth. The experimental results showed that a low concentration of Te precursor will definitely influence the growth procedure. The UV–visible absorption spectra, as well as transmission electron microscopy (TEM) shows the QDs a good monodispersity at any interval of the reaction procedure. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs have high crystallinity and cubic structure. The size and composition-dependent fluorescent emission wavelength of the resultant CdxZn1-xTe alloyed QDs can be tuned from 460 to 610 nm, and their photoluminescent quantum yield can reach up to 70%. Especially in the wavelength range of 510–578 nm, the overall PL QYs of the as-prepared CdxZn1-xTe QDs were above 50%. The current work suggests that electrochemical method is an attractive approach to the synthesis of high-quality II-VI ternary alloyed semiconductor QDs at large-scale with a prominent cost advantage.

An On-line Strategy based on Rolling State Prediction for Hybrid Energy Storage System of Tram

Yu Wang,Zhongping Yang,Fei Lin,Xiaochun Fang,Xingkun An,Hongda Zhou 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

This paper aims at a hybrid tram with the onboard battery-supercapacitor storage system. This paper proposes an on-line strategy based on rolling state prediction (ROS). A wavelet neural network (WNN) is used to predict the running state of the tram in a certain period of time in the future according to the historic data, and the dynamic programming (DP) algorithm is used to optimize the energy management strategy (EMS) during the period. The strategy aims to optimize the system efficiency and battery life. Compared with classical rule-based (RB) strategy, ROS greatly increases the system efficiency and lengthens lifespan of battery and achieves real-time optimization.

Shear Behavior of Marlstone Containing Parallel Fissure under Normal Unloading

Zhiming Yin,Xinrong Liu,Zhongping Yang,Yanlei Wang 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.4

Shear tests under normal unloading were carried out to further study the shear mechanical behavior of marlstone containing parallel fissures. The results reveal that the failure on the rock bridge is tensile failure except for the limited extrusion failure at the tip of the prefabricated fissure. The failure on both sides is generally tensile-shear mixed failure, in which the tensile failure is mainly concentrated in the middle of both sides. In general, it can be summarized as a tensile-shear failure mode of STS-T-STS (S means shear failure, T means tension failure). The failure normal stress of the specimens gradually increases and then decreases with the increase of the fissure inclination, increases with an increase in the initial normal/shear stress, and decreases with the increase of the unloading rate. Strong dilation occurred in the shear process of the specimens, which shows obvious arch effect. The variation law of dilatancy deformation and horizontal deformation in the stage of normal stress unloading is just opposite to that of the failure normal stress. The increasing effect of high shear stress on shear deformation is greater than that of dilatancy deformation, while the inhibiting effect of high normal stress on dilatancy deformation is greater than that of the shear deformation.

Numerical Analysis on the Mechanical Performance of Supporting Structures and Ground Settlement Characteristics in Construction Process of Subway Station Built by Pile-Beam-Arch Method

Xinrong Liu,Yongquan Liu,Zhongping Yang,Chunmei He 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.5

Pile-Beam-Arch (PBA) method is an effective approach to control the surface settlement induced by excavation to construct the subway station, especially when the station is located in the urban area with dense buildings. Based on the numerical analysis model of practical engineering, the whole construction stages of the subway station built by PBA method are simulated in this paper. The mechanical performance of supporting structures (such as piles, beams, arches, secondary lining and backfill concrete) and surface settlement characteristics during construction are investigated. The results show that the pre-supporting system of piles, beams and arches is formed in the stage of soil excavation under main tunnel arch; Station hall plate and backfill concrete are two key structures to ensure the support stiffness of PBA supporting system. In addition, compared to the bottom-up method, the top-down method for the secondary lining construction can obviously reduce the internal force of supporting structures and the surface settlement. Combined with in-situ monitoring data, three increase stages of surface settlement and the corresponding settlement ratio are gained and the characteristic of surface settlement trough is also analysed. This study is helpful for further understanding the support mechanism of PBA method and the increase law of the ground settlement during the construction of the station built by PBA method.

An Improved Central 60° Synchronous Modulation for High Transient Performance with PMSM Stator Flux Control Used in Urban Rail Transit Systems

Xiaochun Fang,Fei Lin,Zhongping Yang 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.2

Central 60° synchronous modulation is an easy pulse-width modulation (PWM) method to implement for the traction inverters of urban rail trains at a very low switching frequency. Unfortunately, its switching patterns are determined by a Fourier analysis of assumed steady-state voltages. As a result, its transient responses are not very good with over-currents and high instantaneous torque pulses. In the proposed solution, the switching patterns of the conventional central 60° modulation are modified according to the dynamic error between the target and actual stator flux. Then, the specific trajectory of the stator flux and current vector can be guaranteed, which leads to better system transients. In addition, stator flux control is introduced to get smooth mode switching between the central 60° modulation and the other PWMs in this paper. A detailed flow chart of the control signal transmission is given. The target flux is obtained by an integral of the target voltage. The actual PMSM flux is estimated by a minimum order flux state observer based on the extended flux model. Based on a two-level inverter model, improved rules in the α-β stationary coordinate system and equations of the switching patterns amendment are proposed. The proposed method is verified by simulation and experimental results.

An Improved Central 60° Synchronous Modulation for High Transient Performance with PMSM Stator Flux Control Used in Urban Rail Transit Systems

Fang, Xiaochun,Lin, Fei,Yang, Zhongping The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.2

Central 60° synchronous modulation is an easy pulse-width modulation (PWM) method to implement for the traction inverters of urban rail trains at a very low switching frequency. Unfortunately, its switching patterns are determined by a Fourier analysis of assumed steady-state voltages. As a result, its transient responses are not very good with over-currents and high instantaneous torque pulses. In the proposed solution, the switching patterns of the conventional central 60° modulation are modified according to the dynamic error between the target and actual stator flux. Then, the specific trajectory of the stator flux and current vector can be guaranteed, which leads to better system transients. In addition, stator flux control is introduced to get smooth mode switching between the central 60° modulation and the other PWMs in this paper. A detailed flow chart of the control signal transmission is given. The target flux is obtained by an integral of the target voltage. The actual PMSM flux is estimated by a minimum order flux state observer based on the extended flux model. Based on a two-level inverter model, improved rules in the α-β stationary coordinate system and equations of the switching patterns amendment are proposed. The proposed method is verified by simulation and experimental results.

A Simplified Synchronous Pulse-Width Modulation Method for Three-level Inverter of High-speed Train

Fei Lin,Qiaona Lian,Jialiang Yuan,Zhongping Yang,Zhiqiang Zhang,Yue Xu,Jinghai Jiao 보안공학연구지원센터 2015 International Journal of Smart Home Vol.9 No.12

The synchronous Pulse-Width Modulation (PWM) is quite complex for three-level neutral point-clamped (NPC) inverter. A simple central 60° synchronous modulation method is presented in this paper for three-level NPC inverter used in the multi-mode PWM strategy. For the fundamental voltage command, the switching angle could be real-time calculated based on this modulation method with different carrier frequency ratios. The switching strategy between these modes is discussed for multi-mode PWM. According to this method, a simulation model of the drive system with three-level inverter and induction motor is built. The simulation results at asynchronous modulation, central 60° synchronous modulation and square wave area, show that the output voltage values can meet the requirements with a good symmetry even in the case of low carrier frequency ratio. The smooth switching among different modes is also accomplished with low impulse current.

Self-adjusting strategy based on rotating injection for sensorless control of high-power PMSM drives

Xiaofan Wang,Xiaochun Fang,Zhi Wang,Zhihong Zhong,Yizhi Wang,Fei Lin,Zhongping Yang 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

As a sensorless control method suitable for permanent magnet synchronous motor (PMSM) at lowspeed, rotating high-frequency injection method will face some special problems in high power applications. On the one hand, the low switching frequency limits the injected signal frequency, which is very close to the fundamental frequency. On the other hand, under heavy load conditions, the fundamental current amplitude is several hundred times of the negative sequence current. This will result in difficulty in signal extraction. In this paper, current spectrum is analyzed quantitatively based on the parameters of PMSM drive for rail vehicles, which illustrates the limitations of conventional bandpass filters. A method based on self-adjusting filter is proposed. The negative sequence current is successfully extracted, and the precise rotor position is obtained under the condition of variable speed and variable load. Based on a fullscale test platform the effectiveness of the proposed method is proved.