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Resonant Charge Current in a Rashba Ring Induced by Spin-Dependent Potential

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Communications in Theoretical Physics 2008年第12期50卷 1453-1456页

作者： JIANG zhan-feng LI Hong Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China College of Physics Science and Information Engineering Hebei Normal University Shijiazhuang 050016 China

A on,dimensional ring subject to Rashba spin-orbit coupling is investigated. When it is attached to a lead with spin-dependent chemical potential, there will be charge current in the ring. The charge current response is resonantly maximized when the Fermi energy of the lead is equal to any energy level of the 1D ring. And if two probes are attached to the ring, the electric voltage between them creates sawtooth-like wave, which indicates the direction of the charge current. A ferromagnetic lead can also induce persistent charge current, which can be detected by magnetization intensity measurement.

关键词： resonant current Rashba ring spin-dependent potential

Nonparametric Inference in a Simple Change-point Model

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Acta Mathematica Sinica,English Series 2008年第9期24卷 1483-1496页

作者： zhan feng Wang Yao Hua Wu and Lin Cheng Zhao Department of Statistics and Finance University of Science and Technology of China Hefei 230026 P. R. China

In this paper, we consider a change point model allowing at most one change, X($\tfrac{i}{n}$\tfrac{i}{n}) = f($\tfrac{i}{n}$\tfrac{i}{n}) + e($\tfrac{i}{n}$\tfrac{i}{n}), where f(t) = α + θ $I_{(t_0 ,1)} $I_{(t_0 ,1)} (t), 0 ≤ t ≤ 1, {e($\tfrac{1}{n}$\tfrac{1}{n}), ..., e($\tfrac{n}{n}$\tfrac{n}{n})} is a sequence of i.i.d. random variables distributed as e with 0 being the median of e. For this change point model, hypothesis test problem about the change-point t0 is studied and a test statistic is constructed. Furthermore, a nonparametric estimator of t0 is proposed and shown to be strongly consistent. Finally, we give an estimator of jump θ and obtain it’s asymptotic property. Performance of the proposed approach is investigated by extensive simulation studies.

关键词： sample median change point extreme distribution Bahadur representation

Composite Quantile Regression Estimation for Left Censored Response Longitudinal Data

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Acta Mathematicae Applicatae Sinica 2018年第4期34卷 730-741页

作者： Li-qun XIAO zhan-feng WANG Yao-hua WU School of Economics and Statistics Guangzhou University Guangzhou 510006 China Department of Statistics and Finance The School of Management University of Science and Technology of China Hefei 230026 China

For left censored response longitudinal data, we propose a composite quantile regression estimator（CQR） of regression parameter. Statistical properties such as consistency and asymptotic normality of CQR are studied under relaxable assumptions of correlation structure of error terms. The performance of CQR is investigated via simulation studies and a real dataset analysis.

关键词： longitudinal data left censored quantile regression randomly weighting

Effect of Mn Content on Microstructure and Cryogenic Mechanical Properties of a 7%Ni Steel

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Acta Metallurgica Sinica(English Letters) 2018年第7期31卷 699-705页

作者： Hong-Wei Cao Xing-Hong Luo Guo-feng zhan Shi Liu School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China CAS Key Laboratory of Nuclear Materials and SafetyAssessment Institute of Metal ResearchChinese Academyof SciencesShenyang 110016China Research and Development Center of Wuhan Iron and Steel(Group)Corp Wuhan 430080China

The effect of Mn content on the microstructure and cryogenic mechanical properties of a 7% Ni steel was investigated within the Mn content range from 0.13% to 0.36%. The microstructure of the steel as determined by optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscattering diffraction and X-ray diffraction was presented, and the low-temperature mechanical properties were given. The size of prior austenite grain did not change a lot as Mn content increased. Film-like reversed austenite, having high stability, was found mainly in the specimens with lower Mn content; however, in the specimen with the highest Mn content, the role of Mn was not obvious in stabilizing reversed austenite. Besides, with increasing Mn content, the amount of reversed austenite at grain boundaries gradually decreased. The variable Mn content had a significant effect on cryogenic toughness~ but not apparent on cryogenic tensile strength or yield strength. An excellent combination of cryogenic tensile and impact properties was obtained when Mn content of steel was 0.13%.

关键词： 7% Ni steel Mn content Microstructure Reversed austenite Cryogenic mechanical properties

Distribution Approximation of Shrinkage Estimate in Censored Regression Model via Randomly Weighting Method

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Acta Mathematicae Applicatae Sinica 2019年第2期35卷 421-434页

作者： Xian-hui LIU zhan-feng WANG Yao-hua WU Department of Statistics and Finance University of Science and Technology of China School of Statistics and Research Center of Applied Statistics Jiangxi University of Finance and Economics

Censored regression("Tobit") model is a special case of limited dependent variable regression model, and plays an important role in econometrics. Based on this model, all kinds of methods for variable or group variable selection have been developed and the corresponding shrinkage parameter estimates are widely studied. However, asymptotic distributions of the shrinkage estimates involve unknown nuisance parameters,such as density function of error term. To avoid estimating nuisance parameters, this paper presents a randomly weighting method to approximate to the asymptotic distribution of the shrinkage estimate. A computation procedure of random approximation is provided and asymptotic properties of the randomly weighting estimates are also obtained. The proposed methods are evaluated with extensively numerical studies and a women labor supply example.

关键词： Censored regression model variable selection asymptotic properties randomly weighting

Influence of Nb Content on Microstructure and Mechanical Properties of a 7%Ni Steel

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Acta Metallurgica Sinica(English Letters) 2018年第9期31卷 975-982页

作者： Hong-Wei Cao Xing-Hong Luo Guo-feng zhan Shi Liu School of Materials Science and Engineering University ofScience and Technology of ChinaShenyang 110016China CAS Key Laboratory of Nuclear Materials and SafetyAssessment Institute of Metal ResearchChinese Academyof SciencesShenyang 110016China Research and Development Center of Wuhan Iron and Steel(Group)Corp Wuhan 430080China

The influence of Nb content on the microstructure and cryogenic mechanical properties of a 7%Ni steel was investigated within the Nb content range from 0 to 0.05%. The microstructure was characterized by optical microscope, scanning electron microscope, transmission electron microscopy and X-ray diffraction, and the low-temperature mechanical property tests were conducted. The Nb addition can effectively refine the prior austenite grains and microstructure of the steel. Fine niobium precipitates with a diameter of about 10-50 nm were observed. They tend to be spherical and locate mainly in the vicinity of grain boundaries. Although there are considerable amounts of reversed austenite forming at grain boundaries in the specimen containing the highest Nb content, no Nb element was detected in such reversed austenite, which implies that Nb element did not affect the formation of the reversed austenite directly. Mechanical test results suggest that the strength of the 7%Ni steel is not simply in relation to the prior austenite grain size, but also depends on the amount of reversed austenite. On the other hand, the grain refinement, enhanced with increasing Nb content, has a good effect on cryogenic toughness.

关键词： 7%Ni steel Nb content Niobium precipitate Reversed austenite Cryogenic mechanical properties

Perspective on low-temperature electrolytes for LiFePO 4-based lithium-ion batteries

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International Journal of Minerals,Metallurgy and Materials 2023年第1期30卷 1-13页

作者： Xianglong Chen Yudong Gong Xiu Li feng zhan Xinhua Liu Jianmin Ma School of Resources Environment and MaterialsGuangxi UniversityNanning 530004China Peking University Science Park Beijing 100871China School of Materials and Energy University of Electronic Science and Technology of ChinaChengdu 611731China School of Transportation Science and Engineering Beihang UniversityBeijing 100871China

The olivine-type lithium iron phosphate(LiFePO_(4))cathode material is promising and widely used as a high-performance lithium-ion battery cathode material in commercial batteries due to its low cost,environmental friendliness,and high *** present,LiFePO_(4)/C sec-ondary batteries are widely used for electronic products,automotive power batteries,and other occasion-related applications with good thermal stability,stable cycle performance,and low room-temperature self-discharge ***,LiFePO_(4)-based battery applications are seriously limited when they are operated in a cold *** outcome is due to a considerable decrease in Li+transport capabilities within the elec-trode,particularly leading to a dramatic decrease in the electrochemical capacity and power performance of the ***,the design of low-temperature electrolytes is important for the further commercial application of LiFePO_(4) *** paper reviews the key factors for the poor low-temperature performance of LiFePO_(4)-based batteries and the research progress of low-temperature ***-cial attention is paid to electrolyte components,including lithium salts,cosolvents,additives,and the development of new *** factors affecting the anode are also ***,according to the current research progress,some viewpoints are summarized to provide suitable modification methods and research suggestions for improving the practicability of LiFePO_(4)/C commercial batteries at low temperat-ures in the future.

关键词： lithium-ion batteries LiFePO_(4) electrolytes low-temperature electrochemical performance

Quasi-topological electromagnetism:Dark energy,dyonic black holes,stable photon spheres and hidden electromagnetic duality

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Science China(Physics,Mechanics & Astronomy) 2020年第4期63卷 73-87页

作者： Hai-Shan Liu zhan-feng Mai Yue-Zhou Li H.Lu Center for Joint Quantum Studies and Department of Physics Tianjin UniversityTianjin 300350China Institute for Advanced Physics&Mathematics Zhejiang University of TechnologyHangzhou 310023China

We introduce the quasi-topological electromagnetism which is defined to be the squared norm of the topological 4-form F ∧ F. A salient property is that its energy-momentum tensor is of the isotropic perfect fluid with the pressure being precisely the opposite to its energy density. It can thus provide a model for dark energy. We study its application in both black hole physics and *** quasi-topological term has no effect on the purely electric or magnetic Reissner-Nordstr o¨m black holes, the dyonic solution is however completely modified. We find that the dyonic black holes can have four real horizons. For suitable parameters, the black hole can admit as many as three photon spheres, with one being stable. Another intriguing property is that although the quasitopological term breaks the electromagnetic duality, the symmetry emerges in the on-shell action in the Wheeler-De Witt patch. In cosmology, we demonstrate that the quasi-topological term alone is equivalent to a cosmological constant, but the model provides a mechanism for the dark energy to couple with other types of matter. We present a concrete example of the quasi-topological electromagnetism coupled to a scalar field that admits the standard FLRW cosmological solutions.

关键词： quasi-topological electromagnetism dark energy black holes photon spheres electromagnetic duality

Change-point estimation for censored regression model

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Science China Mathematics 2007年第1期50卷 63-72页

作者： zhan-feng WANG Yao-hua WU Lin-cheng ZHAO Department of Statistics and Finance University of Science and Technology of ChinaHefei 230026China

In this paper, we consider the change-point estimation in the censored regression model assuming that there exists one change point. A nonparametric estimate of the change-point is proposed and is shown to be strongly... 详细信息

关键词： censored regression least absolute deviance (LAD) change-point strong consistence convergence rate 62F10 62F12