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Strong interlayer coupling and stable topological flat bands in twisted bilayer photonic Moiré superlattices

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Light(Science & Applications) 2022年第10期11卷 2523-2529页

作者： chang-hwan yi Hee Chul Park Moon Jip Park Center for Theoretical Physics of Complex Systems Institute for Basic Science(IBS)Daejeon 34126Republic of Korea

The moiré superlattice of misaligned atomic bilayers paves the way for designing a new class of materials with wide *** this work,we propose a photonic analog of the moiré superlattice based on dielectric resonator *** sharp contrast to van der Waals materials with weak interlayer coupling,we realize the strong coupling regime in a moiré superlattice,characterized by cascades of robust flat bands at large ***,we find that these flat bands are characterized by a non-trivial band topology,the origin of which is the moiré pattern of the resonator *** physical manifestation of the flat band topology is a robust one-dimensional conducting channel on edge,protected by the reflection symmetry of the moiré *** explicitly breaking the underlying reflection symmetry on the boundary terminations,we show that the first-order topological edge modes naturally deform into higher-order topological corner *** work pioneers the physics of topological phases in the designable platform of photonic moiré superlattices beyond the weakly coupled regime.

关键词： topological bands coupling

Bloch theorem dictated wave chaos in microcavity crystals

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Light(Science & Applications) 2023年第6期12卷 994-1000页

作者： chang-hwan yi Hee Chul Park Moon Jip Park Center for Theoretical Physics of Complex Systems Institute for Basic Science(IBS)Daejeon 34126Republic of Korea Department of Physics Pukyong National UniversityBusan 48513Republic of Korea Department of Physics Hanyang UniversitySeoul 04763Republic of Korea

Universality class of wave chaos emerges in many areas of science,such as molecular dynamics,optics,and network *** this work,we generalize the wave chaos theory to cavity lattice systems by discovering the intrinsic coupling of the crystal momentum to the internal cavity *** cavity-momentum locking substitutes the role of the deformed boundary shape in the ordinary single microcavity problem,providing a new platform for the in situ study of microcavity light *** transmutation of wave chaos in periodic lattices leads to a phase space reconfiguration that induces a dynamical localization *** degenerate scar-mode spinors hybridize and non-trivially localize around regular islands in phase *** addition,we find that the momentum coupling becomes maximal at the Brillouin zone boundary,so the intercavity chaotic modes coupling and wave confinement are significantly *** work pioneers the study of intertwining wave chaos in periodic systems and provide useful applications in light dynamics control.

关键词： theory. chaos wave

Impact of non-Hermitian mode interaction on inter-cavity light transfer

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Photonics Research 2022年第5期10卷 1232-1237页

作者： HYEON-HYE YU SUNJAE GWAK JINHYEOK RYU HYUNDONG KIM JI-hwan KIM JUNG WAN RYU CHIL-MIN KIM chang hwan yi Department of Emerging Materials Science DGISTDaegu 42988Republic of Korea Center for Theoretical Physics of Complex Systems Institute for Basic Science(IBS)Daejeon 34126Republic of Korea

Understanding inter-site mutual mode interaction in coupled physical systems is essential to comprehend large compound systems,as this local interaction determines the successive multiple inter-site energy transfer *** the present study,we demonstrate that only the non-Hermitian coupling can correctly account for the light transfer between two coupled optical *** also reveal that the non-Hermitian coupling effect becomes crucial as the system dimension *** results provide important insight for handling general-coupled devices in the subwavelength regime.

关键词： interaction transfer coupling

Hybridization of different types of exceptional points

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Photonics Research 2019年第12期7卷 1473-1478页

作者： JINHYEOK RYU SUNJAE GWAK JAEWON KIM HYEON-HYE YU JI-hwan KIM JI-WON LEE chang-hwan yi CHIL-MIN KIM Department of Emerging Materials Science DGISTDaegu 42988South Korea Institut fur Physik Technische Universitat IlmenauD-98693 IlmenauGermany Samsung Electro-Mechanics Suwon 16674South Korea

A large number of different types of second-order non-Hermitian degeneracies called exceptional points(EPs)were found in various physical systems depending on the mechanism of coupling between *** show that these EPs can be hybridized to form higher-order EPs,which preserve the original properties of the initial EPs before *** a demonstration,we hybridize chiral and supermode second-order EPs,where the former and the latter are the results of intra-disk and inter-disk mode coupling in an optical system comprised of two Mie-scale microdisks and one Rayleigh-scale *** high sensitivity of the resulting third-order EP against external perturbations in our feasible system is emphasized.

关键词： exceptional coupling system

A comprehensive research on wear resistance of GH4169 superalloy in longitudinal-torsional ultrasonic vibration side milling with tool wear and surface quality

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Chinese Journal of Aeronautics 2024年第4期37卷 556-573页

作者： Baoqi chang Zhaoxi yi Fen ZHANG Lian DUAN Ji-an DUAN School of Mechanical and Electrical Engineering Central South UniversityChangsha 410083China State Key Laboratory of High Performance and Complex Manufacturing Central South UniversityChangsha 410083China School of Physics and Electronics Central South UniversityChangsha 410083China

To improve the service and machining performance of the workpiece, the tool wear mechanisms, surface machining quality, and wear resistance in conventional side milling(CSM)and longitudinal-torsional ultrasonic vibration side milling(LTUVSM) of GH4169 superalloy at different cutting lengths are investigated systematically. Tool wear mechanisms are revealed and the correlation between machined surface quality with tool wear is analyzed correspondingly. Tool wear patterns mainly include adhesive wear, diffusion wear, abrasive wear, and chipping *** surface quality is achieved in LTUVSM due to a maximum reduction of flank wear bandwidth and wear rate by 71.9% and 71.5%, respectively, compared to CSM. The friction coefficient,initial wear stage time, and wear volume of dry sliding wear were measured to evaluate the workpiece wear resistance. The maximum reductions in friction coefficient and wear volume in LTUVSM are 18.2% and 15.8% compared to CSM. The regular ultrasonic vibration textures suppress the friction and the growth of contact nodes in the contact area, decreasing the degree of surface wear, which is demonstrated by a 38.8% increase in initial wear stage time compared to *** conclusion, the workpiece in LTUVSM exhibits higher wear resistance because of the improvement of tool wear and the guarantee of surface quality.

关键词： Dry sliding wear Surface quality Tool wear Ultrasonic vibration Wear resistance

Mathematical Model,Numerical Simulation and Convergence Analysis of a Semiconductor Device Problem with Heat and Magnetic Influences

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Acta Mathematicae Applicatae Sinica 2024年第2期40卷 302-319页

作者： chang-feng LI yi-rang YUAN Huai-ling SONG School of Economics Shandong UniversityJinan 250100China Institute of Mathematics Shandong UniversityJinan 250100China College of Mathematics and Econometrics Hunan UniversityChangsha 410082China

In this paper,the authors discuss a three-dimensional problem of the semiconductor device type involved its mathematical description,numerical simulation and theoretical *** important factors,heat and magnetic influences are *** mathematical model is formulated by four nonlinear partial differential equations(PDEs),determining four major physical *** influences of magnetic fields are supposed to be weak,and the strength is parallel to the *** elliptic equation is treated by a block-centered method,and the law of conservation is *** computational accuracy is improved one *** equations are convection-dominated,thus are approximated by upwind block-centered *** difference can eliminate numerical dispersion and nonphysical *** diffusion is approximated by the block-centered difference,while the convection term is treated by upwind ***,the unknowns and adjoint functions are computed at the same *** characters play important roles in numerical computations of conductor device *** the theories of priori analysis such as energy estimates,the principle of duality and mathematical inductions,an optimal estimates result is *** a composite numerical method is shown for solving this problem.

关键词： three-dimensional conductor device problem with heat and magnetic influences upwind blockcentered differences elemental conservation of mass numerical analysis

Phase Patterning of Poly(oxime-ester)for Information Encryption by Photo-induced Isomerization

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Chinese Journal of Polymer Science 2024年第10期42卷 1488-1494,I0010页

作者： Yu-Fan Yang Yun Bai yi-Bao Li chang-Fei He School of Chemistry and Chemical Engineering Gannan Normal UniversityGanzhou341000China

Crystal polymers or liquid crystal elastomers undergo a phase transition that results in a change in the corresponding optical properties,which has the potential to be applied in areas such as information encryption and *** utilization of these materials for patterning purposes requires different phase transition ***,once prepared,altering the phase transition temperature of them presents significant ***,a poly(oxime-ester)(POE)network is developed to achieve high-resolution and multilevel patterning by photo-induced *** as-prepared POE exhibits the ability to transition from an opaque state to a transparent state under temperature stimuli,with the transition temperature and kinetics dependent on UV light exposure ***,complex patterns and information can be encrypted through different selective regional exposure time and decrypted under specific temperature or cooling ***,we illustrate an example of temporal communication,where cooling time or temperature serves as the encoded *** research expands the application scope of advanced encryption materials,showcasing the potential of POE in dynamic information encryption and decryption processes.

关键词： Poly(oxime-ester) Isomerization Phase patterning Information encryption

Broadband absorption performance of 3D-printed polyetheretherketone-based electromagnetic wave-absorbing composites

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Chinese Journal of Aeronautics 2024年第8期37卷 547-558页

作者： Lin BAI Nan chang Meiying ZHAO Chi HOU yi CAO Dichen LI School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China Chengdu Aircraft Design and Research Institute Chengdu 610091China Xi’an Key Laboratory of Advanced Structure Design and Application of Aircraft Northwestern Polytechnical UniversityXi’an 710072China State Key Laboratory for Manufacturing System Engineering Xi’an Jiaotong UniversityXi’an 710054China

The rapid development of additive manufacturing technology has offered a new avenue for designing and fabricating high wave-absorbing meta *** this study,the mechanical properties and broadband absorption performance of Poly-Ether-Ether-Ketone(PEEK)–based electromagnetic wave–absorbing composite materials was *** high-performance polymer PEEK was used as the matrix,and the materials with electromagnetic wave loss,such as reduced graphene oxide,Carbonyl Iron(CI),and Flake CI(FCI),were used as *** on the theory of impedance matching,a wave-absorbing structure with a gradual impedance gradient was designed and *** test results showed that at the 2.0–18.0 GHz frequency band,the coverage rate of the effective absorption bandwidth was up to 72.0%,the average optimal reflectivity was–18.09 dB,and the wide-angle absorption range was 0°–30°.The advantages of additive manufacturing technology in designing and fabricating wave-absorbing structures are presented,demonstrating that the technology is an effective method for creating broadband absorbing structures.

关键词： Absorption performance Additive manufacturing Electromagnetic absorption PEEK composite materials Gradual structure Broadband absorption

Enhancement of low-temperature toughness of Fe-Mn-C-Al alloy by rare earth Ce-modified inclusions

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Journal of Iron and Steel Research International 2024年第1期31卷 157-173页

作者： Guang-kai Yang chang-ling Zhuang yi-zhuang Li Chen Hu Shao-bo Li College of Materials and Metallurgy Guizhou UniversityGuiyang550025GuizhouChina Department of Mechanical Engineering University of Hong KongHong Kong999077China The State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang110819LiaoningChina State Key Laboratory of Public Big Data Guizhou UniversityGuiyang550025GuizhouChina

Fe-Mn-C-Al alloys have been recognized as promising materials for certain low-temperature applications due to their exceptional mechanical properties and ***,their limited low-temperature toughness restricts their large-scale applications in specific *** influence of trace amounts of rare earth cerium(Ce)on the low-temperature toughness of Fe-18Mn-0.6C-1.8Al alloys was *** addition of Ce effectively alters the inclu-sions in the alloy,transforming large-sized irregular inclusions into fine ellipsoidal rare earth *** leads to a significant reduction in both the proportion and average size of the inclusions,resulting in their effective dispersion throughout the matrix and improved cryogenic *** presence of Ce-containing inclusions within the matrix reduces stress concentration,thereby inhibiting microcrack formation and improving impact absorption ***-cally,the addition of rare earth Ce alters the fracture behavior of the material at room temperature and low temperature,changing from brittle cleavage fracture to a more ductile failure *** impact toughness of the Fe-Mn-C-Al alloy is significantly improved by the addition of 0.0048 wt.%Ce,particularly at-196℃where the impact toughness reaches 103.6 J/cm^(2),representing an impressive improvement of 87.3%.

关键词： Fe-Mn-C-Al alloy Rare earth Low-temperature toughness Inclusion Fracture