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On the half-quantized Hall conductance of massive surface electrons in magnetic topological insulator films

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Science China(Physics,Mechanics & Astronomy) 2024年第6期67卷 127-136页

作者： Rui Chen Shun-qing shen Department of Physics The University of Hong KongHong Kong 999077China Department of Physics Hubei UniversityWuhan 430062China

In topological insulators,massive surface states resulting from local symmetry breaking were thought to exhibit a half-quantized Hall conductance,obtained from the low-energy effective model in an infinite Brillouin *** a lattice model,the surface band is composed of a combination of surface states and bulk *** massive surface states alone may not be enough to support an exact one-half quantized surface Hall conductance in a finite Brillouin zone and the whole surface band always gives an integer quantized Hall conductance as enforced by the TKNN *** explore this,we investigate the band structures of a lattice model describing the magnetic topological insulator film that supports the axion insulator,Chern insulator,and semi-magnetic topological insulator *** reveal that the gapped and gapless surface bands in the three phases are characterized by an integer-quantized Hall conductance and a half-quantized Hall conductance,*** propose an effective model to describe the three phases and show that the low-energy dispersion of the surface bands inherits from the surface Dirac *** gapped surface band manifests a nearly half-quantized Hall conductance at low energy near the center of Brillouin zone,but is compensated by another nearly half-quantized Hall conductance at high energy near the boundary of Brillouin zone because a single band can only have an integer-quantized Hall *** gapless band hosts a zero Hall conductance at low energy but is compensated by another half-quantized Hall conductance at high energy,and thus the half-quantized Hall conductance can only originate from the gapless ***,we calculate the layer-resolved Hall conductance of the *** conclusion suggests that the individual gapped surface band alone does not support the half-quantized surface Hall effect in a lattice model.

关键词： magnetic topological insulator Dirac equation half-quantized Hall conductance

A Novel Carrier Leakage Cancellation Algorithm for Multiple Target Detection

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Chinese Journal of Electronics 2019年第1期28卷 100-106页

作者： ZHOU Junwei shen qing CUI Wei School of Information and Electronic Beijing institute of Technology

False alarms and misdetections caused by the carrier leakage problem attract increasing attention for resource-limited platforms. To tackle the problem, we propose a target protected carrier leakage cancellation algorithm to rebuild the leakage signal from reference cells with those cells randomly updated based on each detection result to exclude the targets. The proposed algorithm eliminates the carrier leakage effectively without introducing false target due to the non-involvement of the target information in the reference cells based on a random update strategy. The noise level of our proposed algorithm is less than that of the commonly used algorithms such as the Cell average constant false alarm rate(CA-CFAR)detection method. As verified in the simulations, the proposed algorithm performs better than the CA-CFAR method.

关键词： Carrier leakage Multiple target Target protected cancellation

Flexible and Accurate Frequency Estimation for Complex Sinusoid Signal by Interpolation Using DFT Samples

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Chinese Journal of Electronics 2018年第1期27卷 109-114页

作者： XIANG Jinzhi CUI Wei shen qing School of Information and Electronics Beijing Institute of Technology

A flexible and accurate frequency estimator is first proposed for frequency estimation of a complex sinusoid weighted with a rectangular window function in additive white Gaussian noise. This proposed frequency estimator can be operated in the application of an arbitrary length discrete Fourier transform where the original input data is padded with any zeroes, which makes it more flexible in practice. The proposed frequency estimator utilizes the maximum sample value and its two adjacent samples in the frequency domain to perform the fine frequency estimation with unbiased results obtained. Then a modified frequency estimator is proposed to estimate the frequency when the complex sinusoid signal is weighted with different nonrectangular window functions. Although the modified frequency estimator is nonanalytic and biased, it can still improve the estimation performance for certain applications. Simulation results demonstrate that both of the proposed frequency estimators are effective to achieve the high frequency estimation accuracy. And the root mean square errors of the proposed frequency estimators approach the Cramer-Rao bound when the signal-to-noise ratio is large enough to make the coarse frequency estimation work effectively.

关键词： Frequency estimation Complex sinusoid DFT interpolation Zero-padding

Sparse Reconstruction Method for DOA Estimation Based on Dynamic Dictionary and Negative Exponent Penalty

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Chinese Journal of Electronics 2018年第2期27卷 386-392页

作者： QIAN Tong CUI Wei shen qing School of Information and Electronic Beijing Institute of Technology

This paper proposes a novel sparse representation method for direction of arrival estimation based on dynamic dictionary and negative exponent penalty. The dynamic dictionary can eliminate the off-grid effect and the negative exponent penalty is capable of strengthening the sparse constraint to improve the performance. The basis is regarded as a part of the optimal target and the cross iteration is utilized to jointly update the dictionary and sparse support in this method. Based on the propositions of the penalty function, the penalty function is designed to replace of 1 norm because of its unbiasedness and stronger sparse constraint. The regularization parameter is simplified as a constant due to pre-white process, which greatly extends the application range of the proposed method. The simulation results show that the proposed method can efficiently reduce the off-grid effect and the over-complete rate of the original dictionary. Compared with the conventional sparse representation methods, it has better performance and lower computation complexity.

关键词： Direction of arrival(DOA) Sparse reconstruction Dynamic dictionary Penalty function

Self-assembly and pH-Responsive Properties of Poly(L-glutamic acid-r-Lleucine) and Poly(L-glutamic acid-r-L-leucine)-b-Polysarcosine

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Chinese Journal of Polymer Science 2015年第8期33卷 1186-1195页

作者： Ce Tian 凌君 You-qing shen MOE Key Laboratory of Macromolecular Synthesis and Functionalization Department of Polymer Science and EngineeringZhejiang University Department of Chemical and Biological Engineering Zhejiang University

Polypeptides and polypeptoids were widely used as biomedical materials because of their good biocompatibility. In this work we reported a series of pH-responsive copolypeptides and polypeptide-polypeptoid block copolymers, i.e. random copolymers of L-glutamic acid （Glu） with L-leucine （Leu） [poly（Glu-r-Leu）s], as well as their block copolymers with polysarcosine （polySar）. Well-defined poly（Glu-r-Leu）s with predictable compositions and molecular weights were synthesized by ring opening polymerization of corresponding N-carboxyanhydride monomers. We investigated the relationship between hydrophilicity-hydrophobicity transition and copolymer composition. With increasing Leu fraction, both the pH value of cloud point and the micellar size increased. Poly（Glu-r-Leu） with 60% Leu exhibited a cloud point at the pH of 5.0 to 6.0 the same as that in endosome and lysosome. Poly（Glu-r-Leu）-b-polySars assembled in phosphate buffer and performed pH-responsive morphology change from orbicular micelles at high pH to worm-like micelles at low pH. They were potential pH-responsive carriers for drug and gene delivery to enhance cargo release in cellules.

关键词： α-Amino acid NCA Random/block copolypeptide pH-Responsive Hydrophilicity-hydrophobicity transition.

The family of topological phases in condensed matter

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National Science Review 2014年第1期1卷 49-59页

作者： Shun-qing shen Department of Physics The University of Hong Kong

he discovery of topological insulators and superconductors is an important advance in condensed mater *** phases relect global properties of the quantum states in materials,and the boundary states are the characteristic of the *** phases constitute a new branch in condensed mater *** a historic development is briely introduced,and the known family of phases in condensed mater are summarized.

关键词： topological insulator quantum spin Hall efect quantum Hall efect topological superconductor Dirac equation

Quantum transport in topological semimetals under magnetic fields

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Frontiers of physics 2017年第3期12卷 43-60页

作者： Hai-Zhou Lu Shun-qing shen Department of Physics The University of Hong Kong Pokfulam Road Hong Kong China

Topological semimetals are three-dimensional topological states of matter, in which the conduction and valence bands touch at a finite number of points, i.e., the Weyl nodes. Topological semimetals host paired monopoles and antimonopoles of Berry curvature at the Weyl nodes and topologically protected Fermi arcs at certain surfaces. We review our recent works on quantum transport in topo- logical semimetals, according to the strength of the magnetic field. At weak magnetic fields, there are competitions between the positive magnetoresistivity induced by the weak anti-localization effect and negative magnetoresistivity related to the nontrivial Berry curvature. We propose a fitting formula for the magnetoconductivity of the weak anti-localization. We expect that the weak localization may be induced by inter-valley effects and interaction effect, and occur in double-Weyl semimetals. For the negative magnetoresistance induced by the nontrivial Berry curvature in topological semimetals, we show the dependence of the negative magnetoresistance on the carrier density. At strong magnetic fields, specifically, in the quantum limit, the magnetoconductivity depends on the type and range of the scattering potential of disorder. The high-field positive magnetoconductivity nmy not be a com- pelling signature of the chiral anomaly. For long-range Gaussian scattering potential and half filling, the magnetoconductivity can be linear in the quantum limit. A minimal conductivity is found at the Weyl nodes although the density of states vanishes there.

关键词： topological semimetal magnetoconductivity magnetoresistance localization,anti-localization chiral anomaly

An Implementation Model of Parlay MMCCS API Based on SIP

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The Journal of China Universities of Posts and Telecommunications 2006年第2期13卷 43-49页

作者： GUAN You-qing shen Su-bin Research Center of Network Technology Nanjing University of Posts and Telecommunications Nanjing 210003 P.R. China

Parlay Multi Media Call Control Services （ MMCCS） Application Programming Interfaces （API） based on Session Initiation Protocol （SIP） is essential for the implementation of Parlay Call Control （ CC） API. This paper first proposes an implementation model of Parlay MMCCS API based on SIP, then presents a mapping between SIP and MMCCS AP1 as far as methods and parameters are concerned, illustrates corresponding relationships between different components of SIP and MMCCS API by means of an application collaboration diagram, and finally presents an application using Java codes as well as some SIP messages. The application shows that a majority of MMCCS API based on SIP can be implemented and therefore verifies our mapping between MMCCS API and SIP.

关键词： SIP parlay MMCCS API

A FIFTH-ORDER ACCURATE WEIGHTED ENN DIFFERENCE SCHEME AND ITS APPLICATIONS

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Journal of Computational Mathematics 2001年第5期19卷 531-538页

作者： Yi-qing shen Ru-quan Wang Hong-zhi Liao Department of Mathematics Yunnan UniversityKunming 650091China ICMSEC Academy of Mathematics and Systems SciencesChinese Academy of SciencesBeijing 100080China

Presents a study which constructed a high accurate difference scheme based on the ENN scheme. Overview of ENN scheme and several high order accuracy central schemes; Numerical method used; Relation between the weighte... 详细信息

关键词： ENN scheme WENO scheme shock-boundary-layer interaction