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Anticrossing Due to Resonant Coupling of Hole Levels in Asymmetric Coupled- Quantum- Wells

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Chinese Physics Letters 1993年第7期10卷 433-436页

作者： xu shijie JIANG Desheng LI Guohua ZHANG Yaohui LUO Jinsheng National Laboratory for Superlattices and Microstructures Institute of SemiconductorsAcadcniia Sinica.Beijing 100083 Department of Electronic Engineering Xi’an Jiaotong UniversityXi’an 710049

We present distinct evidence of anticrossing behavior for excitonic transitions due to resonant coupling of heavy-hole ground levels in a biased GaAs/Al_(0.35) Ga_(0.65)As/GaAs(50/40/100Å)asymmetric coupled-double-qua... 详细信息

关键词： Coupling Quantum resonant

Storage and transfer of optical excitation energy in GaInP epilayer:Photoluminescence signatures

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Journal of Materials Science & Technology 2019年第7期35卷 1364-1367页

作者： shijie xu Ying Huang Zhicheng Su Rongxin Wang Jianrong Dong Deliang Zhu Department of Physics and Shenzhen Institute of Research and Innovation (HKU-SIRI)The University o f Hong KongPokfulam RoadHong KongChina Vacuum Interconnected Nanotech Workstation Suzhou Institute of Nano-tech and Nano-bionicsChinese Academy of SciencesSuzhou215123China Guangdong Research Center for Interfacial Engineering of Functional Materials and College of Materials Science and EngineeringShenzhen UniversityShenzhen518060China

GaInP alloy could be the most trusted key material for fabricating super-high-efficiency single-and multijunction solar cells, especially for space applications. The storage and transfer of optical excitation energy in this key alloy is thus a key subject of the energy conversion from optical to electrical. In this article we present a study of the subject through investigating photoluminescence(PL) degradation in the GaInP epilayer at 4 K under the continuous optical excitations of ultraviolet(UV) 325 nm, visible 488.0 and 514.5 nm lasers. It is found that the decline of PL intensity with the irradiation time may be represented by I(t)/I0=(1 + tτ-1)-1+C, where I0 is the luminescence intensity at the beginning of irradiation, a time constant, and C a background. Moreover, the PL degradation degree reduces with increasing the excitation wavelength. In addition, some red shift of the PL peak is observed accompanying with the intensity decline under the UV laser excitation. These PL signatures indicate that the localized carriers within the local atomic ordering domains play a major role in the storage and transfer of the excitation energy via photon recycling processes.

关键词： GaInP alloy Photoluminescence Energy transfer Photon recycling

An improved constrained steering law for SGCMGs with DPC

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Acta Mechanica Sinica 2009年第5期25卷 713-720页

作者： Lei Jin shijie xu Department of Guidance, Navigation and Control,School of Astronautics, Beihang University, 100191 Beijing, China Department of Guidance Navigation and Control School of Astronautics Beihang University Beijing China

An improved constrained （IC） steering law for single gimbal control moment gyros （SGCMGs） with deformed pyramid configuration （DPC） is proposed, First of all, the original system with five pyramid configuration （FPC） whose two adjacent gyros are in failure state is reconfigured as a degraded system with DPC. Then, the singular angular momentum hypersurfaces of the original and the degraded systems are plotted via the singular angular momentum equa- tion of SGCMGs. Based on singular surfaces, the differences between FPC and DPC in singularity and momentum envelope are obtained directly, which provide an important reference for steering law design of DPC. Finally, an IC steering law is designed and applied to DPC. The simulation results demonstrate that the IC steering law has advantages in simplicity of calculation, avoidance of singularity and exactness of output torque, which endow the degraded system with fine controllability in a restricted workspace.

关键词： Single gimbal control moment gyros (SGCMGs) - Deformed pyramid configuration (DPC) Failure Singularity - Steering law

Extinction of the zero-phonon line and the first-order phonon sideband in excitonic luminescence of ZnO at room temperature： the self-absorption effect

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Science Bulletin 2017年第22期62卷 1525-1529页

作者： Honggang Ye Zhicheng Su Fei Tang Changcheng Zheng Guangde Chen Jian Wang shijie xu Department of Physics and Shenzhen Institute of Research and Innovation (HKU-SIRI) The University of Hong Kong Hang Kong China Department of Applied Physics Xi'an Jiaotong University Xi'an 710049 China Mathematics and Physics Centre Department of Mathematical Sciences Xi'an Jiaotong-Liverpool University Suzhou 215123 China

It is firmly demonstrated in experiment that the self-absorption(SA) effect can lead to the extinction of the zero-phonon line and the first-order longitudinal optical phonon sideband of free excitonic luminescence of ZnO at room temperature. Moreover, effectiveness degree of SA effect is found to be dependent on both absorption coefficient and travelling distance of emitted photons, as well as even lattice temperature, which is uniquely reflected by the redshift amount in emission peak in ZnO. It is also unambiguously proved that the SA effect still strictly obeys the Beer-Lambert law of absorption. This work not only uncovers the long-term puzzle of significant redshift of emission peak of ZnO at higher temperatures, but also shows that the SA effect may have to be carefully taken into consideration in the study of spontaneous emission, laser and relevant optoelectronic processes in luminescent materials and optoelectronic devices.

关键词： Seif-absorption Excitonic luminescence Two-photon absorption Phonon-assistecl luminescence

An Empirical Research on Metropolitanization and Housing Price Differentiation Based on the Data of 31 Provincial Capitals and Municipalities with Independent Planning Status in China

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Journal of Systems Science and Information 2022年第5期10卷 445-465页

作者： Shengguo LI Xiaodong DING shijie xu Jichang DONG Zhi DONG School of Economics and Management University of Chinese Academy of SciencesBeijing 100190China Weiqiao Guoke Joint Laboratory University of Chinese Academy of SciencesBeijing 100190China

Under the background of population aggregation in megacities,some adjustments are made to the urbanization strategy,whose focus is shifted to the development of megacities and megacity ***,the housing price differentiation among cities tends to become increasingly *** paper,from the perspective of population mobility,takes provincial capitals and municipalities with independent planning status(PCs&MIPSs)as research samples to evaluate the level of housing price differentiation within provincial-level administrative divisions of China,and analyze from the perspective of demand side how the metropolitanization effects regarding the population formed due to population aggregation in megacities affect the housing prices of megacities and the housing price difference between megacities and other *** research found that:1)The increasing net inflow of population boosts the housing prices and accelerate the housing price differentiation;2)The impact of the increasing net inflow of population on housing price increases and housing price differentiation has regional heterogeneity and city size heterogeneity;3)The income gap strengthens the effect of population inflow upon the housing price differentiation.

关键词： metropolitanization population aggregation housing price differentiation

High-excited-state splitting and multimode vibrational coupling in Mn^(4+)-activated fluoride phosphor

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Science China(Physics,Mechanics & Astronomy) 2024年第3期67卷 95-101页

作者： Debao Zhang Wanggui Ye xuguang Cao Ji Zhou Fei Tang Changcheng Zheng Jiqiang Ning shijie xu Department of Optical Science and Engineering School of Information Science and TechnologyFudan University Shanghai 200438China Jiangsu Key Laboratory of Advanced Laser Materials and Devices Schoolof Physics and Electronic Engineering Jiangsu Normal UniversityXuzhou 221116China Division of Natural and Applied Sciences Duke Kunshan UniversityKunshan 215316China

Excited-states play a crucial role in the optical absorption and luminescence of solids and hence their accurate information is highly desired. Herein, we attempt to seize the excited-states information of Mn^(4+)ions in K_(2)SiF_(6) microcrystals via measuring and calculating their variable-temperature photoluminescence excitation(PLE) spectra. At cryogenic temperatures, an unpredicted splitting of the high-excited-state is observed. Moreover, the two-split high-excited-state levels are further revealed to primarily couple with the two hyperfine split modes of quasi-localized ν2 vibration in the distorted Mn-F_(6) octahedral configuration,whereas the coupling strengths are found to be substantially different from each other. The slightly split vibrational mode is firmly supported by the low-temperature Raman spectra. Jahn-Teller lattice distortion is believed to be responsible for the observed splitting of the electronic high-excited-state and the quasi-localized vibrational mode.

关键词： splitting of excited-state photoluminescence excitation spectrum electron-phonon coupling Jahn-Teller effect

Robust Image Hashing via Random Gabor Filtering and DWT

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Computers, Materials & Continua 2018年第5期55卷 331-344页

作者： Zhenjun Tang Man Ling Heng Yao Zhenxing Qian Xianquan Zhang Jilian Zhang shijie xu Guangxi Key Lab of Multi-Source Information Mining&Security Guangxi Normal UniversityGuilin541004China Shanghai Institute of Intelligent Electronics&Systems School of Computer ScienceFudan UniversityShanghai200433China School of Information Systems Singapore Management University178902Singapore

Image hashing is a useful multimedia technology for many applications,such as image authentication,image retrieval,image copy detection and image *** this paper,we propose a robust image hashing based on random Gabor filtering and discrete wavelet transform(DWT).Specifically,robust and secure image features are first extracted from the normalized image by Gabor filtering and a chaotic map called Skew tent map,and then are compressed via a single-level 2-D *** hash is finally obtained by concatenating DWT coefficients in the LL *** experiments with open image datasets are carried out and the results illustrate that our hashing is robust,discriminative and *** operating characteristic(ROC)curve comparisons show that our hashing is better than some popular image hashing algorithms in classification performance between robustness and discrimination.

关键词： Image hashing Gabor filtering chaotic map skew tent map discrete wavelet transform.

Large eddy simulation of spray combustion using flamelet generated manifolds combined with artificial neural networks

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Energy and AI 2020年第2期2卷 33-42页

作者： Yan Zhang shijie xu Shenghui Zhong xue-Song Bai Hu Wang Mingfa Yao State Key Laboratory of Engines Tianjin University135 Yaguan RdTianjin 300350China Department of Energy Sciences Lund UniversityLund 22100Sweden

In the present work,artificial neural networks(ANN)technique combined with flamelet generated manifolds(FGM)is proposed to mitigate the memory issue of FGM models.A set of ANN models is firstly trained using a 68-species mass fractions in mixture fraction-progress variable *** ANN prediction accuracy is examined in large eddy simulation(LES)and Reynolds averaged Navier-Stokes(RANS)simulations of spray *** is shown that the present ANN models can properly replicate the FGM table for most of the species mass *** network models with relative error less than 5%are considered in RANS and LES to simulate the Engine Combustion Network(ECN)Spray H *** of the method is firstly conducted in the framework of *** non-reacting and reacting cases show the present method predicts very well the trend of spray and combustion process under different ambient *** results show that FGM-ANN can replicate the ignition delay time(IDT)and lift-off length(LOL)precisely as the conventional FGM method,and the results agree very well with the *** the help of ANN,it is possible to achieve high efficiency and accuracy,with a significantly reduced memory requirement of the FGM *** with FGM-ANN is then applied to explore the detailed spray combustion *** explosive mode analysis(CEMA)approach is used to identify the local combustion *** is found that before the spray flame is developed to the steady-state,the high CH_(2)O zone is always associated with ignition ***,high CH_(2)O zone together with high OH zone is dominated by the burned mode after the *** lift-off position is dominated mainly by the diffusion mode.

关键词： Flamelet generated manifolds Artificial neural networks Engine combustion network Spray H Chemical explosive mode analysis

Probing defects in ZnO by persistent phosphorescence

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Opto-Electronic Advances 2018年第6期1卷 8-13页

作者： Honggang Ye Zhicheng Su Fei Tang Yitian Bao Xiangzhou Lao Guangde Chen Jian Wang shijie xu Department of Physics and Shenzhen Institute of Research and Innovation (HKU-SIRI) The University of Hong Kong Pokfulam Road Hong Kong China Department of Applied Physics Xi'an Jiaotong University Xi'an 710049 China

Native point defects in ZnO are so complicated that most of them are still debating issues, although they have been studied for decades. In this paper, we experimentally reveal two sub-components usually hidden in the low energy tail of the main broad green luminescence band peaking at 547 nm （-2.267 eV） in intentionally undoped ZnO single crystal by selecting the below-band-gap （BBG） optical excitations （e.g. light wavelengths of 385 nm and 450 nm）. Moreover, both sub-components are manifested as long persistent phosphorescence once the BBG excitations are removed. With the aid of a newly developed model, the energy depths of two electron traps involved within the long lived orange luminescence are determined to be 44 meV and 300 meV, respectively. The candidates of these two electron traps are argued to be most likely hydrogen and zinc interstitials in ZnO.

关键词： zinc oxide defects phosphorescence photoluminescence