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Broadband strong optical dichroism in topological Dirac semimetals with Fermi velocity anisotropy

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chinese Physics B 2020年第7期29卷 128-134页

作者： J Lim K J A Ooi c z.ang L K ang Yee Sin ang Science Math and TechnologySingapore University of Technology and DesignSingapore School of Energy and chemical Engineering Xiamen University MalaysiaSelangor Darul Ehsan 43900Malaysia college of chemistry and chemical Engineering Xiamen UniversityXiamen 361005China School of Physics University of WollongongNorthfields AvenueNew South Wales 2522Australia

Prototypical three-dimensional(3D)topological Dirac semimetals(DSMs),such as cd3As2 and Na3Bi,contain electrons that obey a linear momentum-energy dispersion with different Fermi velocities along the three orthogonal momentum *** being extensively studied in recent years,the inherent Fermi velocity anisotropy has often been neglected in the theoretical and numerical studies of 3D *** this omission does not qualitatively alter the physics of light-driven massless quasiparticles in 3D DSMs,it does quantitatively change the optical coefficients which can lead to nontrivial implications in terms of nanophotonics and plasmonics *** we study the linear optical response of 3D DSMs for general Fermi velocity values along each *** the signature conductivity-frequency scaling,σ(ω)∝ω,of 3D Dirac fermion is well-protected from the Fermi velocity anisotropy,the linear optical response exhibits strong linear dichroism as captured by the universal extinction ratio scaling law,Λi j=(vi/v j)^2(where i=j denotes the three spatial coordinates x,y,z,and vi is the i-direction Fermi velocity),which is independent of frequency,temperature,doping,and carrier scattering *** cd3As2 and Na3Bi3,an exceptionally strong extinction ratio larger than 15 and covering a broad terahertz window is *** findings shed new light on the role of Fermi velocity anisotropy in the optical response of Dirac semimetals and open up novel polarization-sensitive functionalities,such as photodetection and light modulation.

关键词： topological Dirac semimetal optical anisotropy linear dichroismn linear response theory

Determination of surface structure and the depth profile of silica glass by infrared spectroscopy

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光学精密工程 2005年第4期13卷 413-420页

作者： c. z. Tan Laboratory of Solid State Microstructure and Department of Materials Science and Engineering Nanjing University 210093 Nanjing China Institut für Mineralogie Freie Universitt Berlin 14195 Berlin Germany

The surface structure and properties are different from those of the bulk, depending on the substrate materials and deposition condition, and playing an important role in precise optical components. The conventional spectroscopic methods to monitor the surface structure are restricted only in several layers of molecules. It is known that the penetration depth of the incident light increases with its wavelength and decreases with the angle of incidence. Thus infrared spectroscopy provides a powerful means for determination of surface structure and the depth profile up to micrometers. By recording the reflection spectra at different angles of incidence, the surface structure and its depth profile can be monitored successively. Further, the incident field has the subcomponents parallel and perpendicular to the surface, which excite the transverse and longitudinal optic modes, respectively. change of the polarization direction of the incident light provides a practical function to study anisotropic property of the surface and the interaction between the transverse and longitudinal optic modes. In this work, infrared spectrophotometer was applied to investigate the depth profile in microstructure of silica glass. combining with the glass fiber system, this technique can be used for in-situ control of the deposition process. In comparing with ellipsometry, this method reveals both structural and constitutional information.

关键词：硅石光谱红外线表面结构光学材料

Refining constitutive relation by integration of finite element simulations and Gleeble experiments

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Journal of Materials Science & Technology 2019年第6期35卷 1039-1043页

作者： D.J. Yu D.S. Xu H. W ang z.B. zhao G.z. Wei R. Yang college of Sciences Northeastern University Shenyang 110004 China Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

Thermo-mechanical coupled finite element calculations were carried out to simulate the Gleeble compression of the samples of a titanium alloy(Ti60), and the results are analyzed and compared with the actual compression tests conducted on a Gleeble 3800 thermo-mechanical simulator. The changes in temperature, stress and strain distribution in the samples and the source of error on the constitutive relations from Gleeble hot compression test were analyzed in detail. Both simulations and experiments showed that the temperature distribution in the specimen is not uniform during hot compression, resulting in significant deformation inhomogeneity and non-ignorable error in the flow stress strain relation,invalidating the uniform strain assumption commonly assumed when extracting the constitutive relation from Gleeble tests. Based on the finite element simulations with iterative corrections, we propose a scheme to refine the constitutive relations from Gleeble tests.

关键词： Titanium alloy constitutive relation Finite element compression Temperature distribution

Gradient Structured copper by Rotationally Accelerated Shot Peening

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Journal of Materials Science & Technology 2017年第7期33卷 758-761页

作者： X.Wang Y.S.Li Q.z.ang Y.H.zhao Y.T.zhu Nano Structural Materials center School of Materials Science and Engineering Nanjing University of Science and Technology Nanjing 210094 China School of Mechanical Engineering Nanjing University of Science and Technology Nanjing 210094 China Department of Materials Science and Engineering North Carolina State University Raleigh NC 27695 USA

A new technology-rotationally accelerated shot peening（RASP）, was developed to prepare gradient structured materials. By using centrifugal acceleration principle and large steel balls, the RASP technology can produce much higher impact energy compared to conventional shot peening. As a proof-of-concept demonstration, the RASP was utilized to refine the surface layer in pure copper（cu） with an average grain size of 85 nm. The grain size increases largely from surface downwards the bulk, forming an800 ？m thick gradient-structured surface layer and consequently a micro-hardness gradient. The difference between the RASP technology and other established techniques in preparing gradient structured materials is discussed. The RASP technology exhibits a promoting future for large-scale manufacturing of gradient materials.

关键词： Microstructure Rotationally accelerated shot peening Gradient structure Hardness copper

Flocking and clustering in mixtures of self-propelled particles with or without active reorientation

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communications in Theoretical Physics 2023年第11期75卷 135-141页

作者： Lu chen z c Tu Department of Physics Beijing Normal UniversityBeijing 100875China complex Systems Division Beijing Computational Science Research CenterBeijing 100193China

We study phase behaviors of mixtures comprising active particles with and without active reorientation by varying mixing *** observe that the order parameter characterizing flocking in the steady state exhibits a linear decrease with an increase in mixing *** the order parameter characterizing clustering in the steady state presents a sharp leap as the mixing ratio ***,we obtain phase diagrams of flocking under different mixing ratios and observe that the domain corresponding to flocking experiences a contraction with the increase of mixing ***,the coordinates of the critical point on the phase boundary between the flocking and the disordered phase decay exponentially with the mixing ratio.

关键词： active matter flocking clustering binary system

Preliminary performance analysis and optimization based on 1D neutronics model for Indian DEMO HccB blanket

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Plasma Science and Technology 2020年第8期22卷 184-191页

作者： D AGGARWAL c DANANI M z YOUSSEF Institute for Plasma Research GandhinagarGujarat 382428India Homi Bhabha National Institute(HBNI) AnushaktinagarMumbai 400094India University of california-Los angeles Los AngelesCA 90095United States of America

India,under its breeding blanket R&D program for DEMO,is focusing on the development of two tritium breeding blanket concepts;namely the lead-lithium-cooled ceramic breeder and the helium-cooled ceramic breeder(HccB).The study presented in this paper focuses on the neutronic design analysis and optimization from the tritium breeding perspective of the HccB *** Indian concept has an edge-on configuration and is one of the variants of the helium-cooled solid breeder blanket concepts proposed by several partner countries in *** Indian HccB blanket having lithium titanate(Li2TiO3)as the tritium breeder and beryllium(Be)as the neutron multiplier with reduced-activation ferritic/martensitic steel structure aims at utilizing the low-energy neutrons at the rear part of the *** aim of the optimization study is to minimize the radial blanket thickness while ensuring tritium self-sufficiency and provide data for further neutronic design and thermal-hydraulic layout of the HccB *** is found that inboard and outboard blanket thicknesses of 40 cm and 60 cm,respectively,can give a tritium breeding ratio(TBR)>1.3,with 60%6Li enrichment,which is assumed to be sufficient to cover potential tritium losses and associated *** results also demonstrated that the Be packing fraction(PF)has a more profound impact on the TBR as compared to 6Li enrichment and the PF of Li2TiO3.

关键词： DEMO helium-cooled ceramic breeder blanket neutronic optimization study tritium breeding ratio

collision risk assessment of reduced aircraft separation minima in procedural airspace using advanced communication and navigation

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chinese Journal of Aeronautics 2023年第4期36卷 315-337页

作者： Qing cAI Hao Jie ang Sameer ALAM Air Traffic Management Research Institute School of Mechanical&Aerospace EngineeringNanyang Technological University639798Singapore

With the advancement of communication,Navigation and Surveillance(cNS)technolo-gies such as space-based Automatic Dependent Surveillance-Broadcast/contract(ADS-B/c),large separation minima may be reduced in procedural *** is of great significance to know the upper limit of the Reduced Separation Minima(RSM)for a procedural airspace and the corre-sponding consequences on collision risk with specifics of the advanced ADS-B and control interven-tion *** this work,an interactive software is first developed for collision risk *** software integrates the International civil Aviation Organization(IcAO)collision risk models for lateral and longitudinal collision risk calculation for the Singapore procedural *** demonstrate that the lateral and longitudinal collision risk of Singapore procedural airspace with respect to current control procedures meets the IcAO Target Level of Safety(TLS)***,the feasibility of reducing the horizontal separations implemented in the Singapore pro-cedural airspace with respect to advanced cNS techniques is *** is found that if advanced cNS technologies are applied,then the current 50-NM lateral and longitudinal separa-tion standards can be reduced to 22 NM(1 NM=1.825 km)and 20 NM,respectively,to meet the TLS standards based on current demand.A method is then devised to expand the traffic demand by p for p∈[10%,200%].It is found that the minimum lateral and longitudinal separa-tions can be reduced from 50 NM to be within the range of[23,31]NM,and 20 NM,respectively,for p∈[10%,200%],while the collision risk still meets the TLS standards.

关键词： Air transportation collision risk Procedural airspace Separation minima Space-based Automatic Dependent Surveillance-Bro adcast/contract(ADS-B/c)

A numerical method based on boundary integral equations and radial basis functions for plane anisotropic thermoelastostatic equations with general variable coefficients

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Applied Mathematics and Mechanics(English Edition) 2020年第4期41卷 551-566页

作者： W.T.ang X.Wang School of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingapore 639798Singapore Department of Mechanical Engineering National University of SingaporeSingapore 117575Singapore

A boundary integral method with radial basis function approximation is proposed for numerically solving an important class of boundary value problems governed by a system of thermoelastostatic equations with variable coe?cients. The equations describe the thermoelastic behaviors of nonhomogeneous anisotropic materials with properties that vary smoothly from point to point in space. No restriction is imposed on the spatial variations of the thermoelastic coe?cients as long as all the requirements of the laws of physics are satis?ed. To check the validity and accuracy of the proposed numerical method, some speci?c test problems with known solutions are solved.

关键词： elliptic partial differential equation variable coefficient boundary element method radial basis function anisotropic thermoelastostatics

Precise asymptotics in the law of the logarithm for random fields in Hilbert space

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Journal of zhejiang University-Science A(Applied Physics & Engineering) 2007年第4期8卷 651-659页

作者： FU Ke-ang z.ang Li-xin Department of Mathematics Zhejiang University Hangzhou 310027 China

consider the positive d-dimensional lattice z^d（d≥2） with partial ordering ≤, let {XK; K∈z＋^d} be i.i.d, random variables taking values in a real separable Hilbert space （H, ｜｜·｜｜） with mean zero and covariance operator ∑ and set partial sums SN =∑K≤nXK,K,N∈z＋^d. Under some moment conditions, we obtain the precise asymptotics of a kind of weighted infinite series for partial sums SN as ε↓ by using the truncation and approximation methods. The results are related to the convergence rates of the law of the logarithm in Hilbert space, and they also extend the results of （Gut and Spataru, 2003）.

关键词： The law of the logarithm Random field Hilbert space. Tail probabilitv. Truncation method