Beam shaping in nanophotonic systems remains a challenge due to the reliance on complex heuristic optimization procedures.In this work,we experimentally demonstrate a novel approach to topological beam shaping using J...Beam shaping in nanophotonic systems remains a challenge due to the reliance on complex heuristic optimization procedures.In this work,we experimentally demonstrate a novel approach to topological beam shaping using Jackiw-Rebbi states in metasurfaces.By fabricating thin-film dielectric structures with engineered Dirac-mass distributions,we create domain walls that allow precise control over beam profiles.We observe the emergence of Jackiw-Rebbi states and confirm their localized characteristics.Notably,we achieve a flat-top beam profile by carefully tailoring the Diracmass distribution,highlighting the potential of this method for customized beam shaping.This experimental realization establishes our approach as a new mechanism for beam control,rooted in topological physics,and offers an efficient strategy for nanophotonic design.展开更多
[Background]High harmonic cavities are widely used in electron storage rings to lengthen thebunch,lower the bunch peak current,thereby reducing the IBS effect,enhancing the Touschek lifetime,as well asproviding Landau...[Background]High harmonic cavities are widely used in electron storage rings to lengthen thebunch,lower the bunch peak current,thereby reducing the IBS effect,enhancing the Touschek lifetime,as well asproviding Landau damping,which is particularly important for storage rings operating with ultra-low emittance or atlow beam energy.[Purpose]To further increase the bunch length without additional hardware costs,the phasemodulation in a dual-RF system is considered.[Methods]In this paper,turn-by-turn simulations incorporating randomsynchrotron radiation excitation are conducted,and a brief analysis is presented to explain the bunch lengtheningmechanism.[Results]Simulation results reveal that the peak current can be further reduced,thereby mitigating IBSeffects and enhancing the Touschek lifetime.Although the energy spread increases,which tends to reduce thebrightness of higher-harmonic radiation from the undulator,the brightness of the fundamental harmonic can,in fact,beimproved.展开更多
To generate a neutron beam exhibiting a Maxwellian energy distribution with narrow emission angles for measuring the neutron capture reaction rates of the s-process nuclides,a monoenergetic 3.4 MeV proton beam produce...To generate a neutron beam exhibiting a Maxwellian energy distribution with narrow emission angles for measuring the neutron capture reaction rates of the s-process nuclides,a monoenergetic 3.4 MeV proton beam produced by the tandem-accelerator in the China Institute of Atomic Energy was utilized.The proton beam was first transmitted through a 60.5μm aluminum foil and then impinged on a natural LiF target to produce neutron beam via^(7)Li(p,n)7Be reaction.The quasi-Gaussian energy distribution of protons in the LiF target resulted in neutron energy spectra that agreed with a Maxwellian energy distribution at kT=(22±2)keV,which was achieved by integrating neutrons detected within an emission angle of 65.0°±2.6°using a ^(6)Li glass detector positioned at 65°relative to the proton beam direction.The narrow angular spread of the Maxwelliandistributed neutron beam enables direct measurement of neutron capture cross-sections for most s-process nuclides,overcoming previous experimental limitations associated with broad angular distributions.展开更多
Interplay between topology and magnetism can give rise to exotic properties in topological materials.Two-dimensional bismuth has been extensively studied owing to its topological states with a strong spin-orbit coupli...Interplay between topology and magnetism can give rise to exotic properties in topological materials.Two-dimensional bismuth has been extensively studied owing to its topological states with a strong spin-orbit coupling,and 1T-VTe_(2)monolayer theoretically predicted to host an intrinsic magnetism as experimentally suggested.In this work,we successfully constructed a vertical heterostructure composed of the two-dimensional Bi(110)monolayer and 1T-VTe_(2)monolayer by using molecular beam epitaxy(MBE).Scanning tunneling microscopy(STM)measurements revealed that the growth of Bi preferably occurs along the step edges of the VTe_(2)monolayer,forming a Bi(110)monolayer on top of the VTe_(2)monolayer next to a peripheral Bi bilayer.The Bi(100)/VTe_(2)heterostructure exhibits a specific lattice registry with a well-defined moiréperiodicity.Scanning tunneling spectroscopy(STS)measurements further unveiled an universal suppression in the local density-of-states at the boundary of the Bi(110)/VTe_(2)bilayer.By examining the atomic structures of Bi(110)boundaries,we found this effect does not originate from the previously proposed atomic reconstruction at the step edge of Bi(110),but is likely related to the magnetic properties of the VTe_(2)monolayer.展开更多
For 5G millimeter wave(mm-Wave)user equipments(UEs),all test cases must be evaluated in Over-The-Air(OTA)manner.Test time increases dramatically compared to Sub-6 GHz.Therefore,test time reduction is of great signific...For 5G millimeter wave(mm-Wave)user equipments(UEs),all test cases must be evaluated in Over-The-Air(OTA)manner.Test time increases dramatically compared to Sub-6 GHz.Therefore,test time reduction is of great significance for 5G mm-Wave OTA testing.Among all test cases,beam peak search is the most time-consuming,taking up the majority of the overall test time.Therefore,the objective of this work is to determine a suitable beam peak search grid for 5G mm-Wave UEs with satisfactory accuracy and efficiency.Through radiation property investigation of 5G mm-Wave commercial UEs,more reasonable reference array configuration(4×2)and reference deployment scenario(composite beam)are proposed for beam peak search grid analysis.The effect of different grid configurations on beam peak search precision are characterized quantitatively.The determination of associated measurement uncertainty(MU)term along with quantitative analysis approach are proposed based on statistical analysis.Finally,the recommended minimum number of beam peak search grid points is 182 based on the proposed 4×2 array under composite beam scenario.Compared with currently-required 1106 points in 3GPP/CTIA specifications,over 80%reduction can be achieved without increasing the MU limit.The feasibility of the proposed MU analysis as well as the recommended grids is demonstrated through measurements.展开更多
Electron beam injectors are pivotal components of large-scale scientific instruments,such as synchrotron radiation sources,free-electron lasers,and electron-positron colliders.The quality of the electron beam produced...Electron beam injectors are pivotal components of large-scale scientific instruments,such as synchrotron radiation sources,free-electron lasers,and electron-positron colliders.The quality of the electron beam produced by the injector critically influences the performance of the entire accelerator-based scientific research apparatus.The injectors of such facilities usually use photocathode and thermionic-cathode electron guns.Although the photocathode injector can produce electron beams of excellent quality,its associated laser system is massive and intricate.The thermionic-cathode electron gun,especially the gridded electron gun injector,has a simple structure capable of generating numerous electron beams.However,its emittance is typically high.In this study,methods to reduce beam emittance are explored through a comprehensive analysis of various grid structures and preliminary design results,examining the evolution of beam phase space at different grid positions.An optimization method for reducing the emittance of a gridded thermionic-cathode electron gun is proposed through theoretical derivation,electromagnetic-field simulation,and beam-dynamics simulation.A 50%reduction in emittance was achieved for a 50 keV,1.7 A electron gun,laying the foundation for the subsequent design of a high-current,low-emittance injector.展开更多
The effects of initial spin orientation on the final electron beam polarization in laser wakefield acceleration in a pre-polarized plasma are investigated theoretically and numerically.From the results of variation of...The effects of initial spin orientation on the final electron beam polarization in laser wakefield acceleration in a pre-polarized plasma are investigated theoretically and numerically.From the results of variation of the initial spin direction,the spin dynamics of the electron beam are found to depend on the self-injection mechanism.The effects of wakefields and laser fields are studied using test particle dynamics and particle-in-cell simulations based on the Thomas-Bargmann-Michel-Telegdi equation.Compared with transverse injection,longitudinal injection is found to be preferable for obtaining a highly polarized electron beam.展开更多
Traditional dynamic analysis of mechanical structures,often limited to individual beams or plates,fails to fully capture their dynamic behaviors.In systems where space and mass are constrained,such as the battery supp...Traditional dynamic analysis of mechanical structures,often limited to individual beams or plates,fails to fully capture their dynamic behaviors.In systems where space and mass are constrained,such as the battery support structures in electric aircraft,conventional absorbers and isolators are insufficient for effective vibration control.This study simplifies the battery support structure of electric aircraft as an integrated composite beam consisting of three interconnected beams,and investigated its structural dynamics properties and nonlinear vibration control under thermal conditions caused by battery heat.The nonlinear vibration control is performed using the Nitinol steel wire ropes(Ni Ti-ST),with nonlinear damping properties.The natural frequencies of system are determined using the Rayleigh-Ritz technique.Theoretical results are validated through both Finite Element Method(FEM)and hammer tests.Moreover,the dynamic equations are derived using the Lagrange method and discretized via the Galerkin Truncation Method(GTM).The Harmonic Balance Method(HBM)is used to evaluate the vibration responses of the integrated model,with further verification through the Runge-Kutta Method(RKM).The experiments are conducted to corroborate the theoretical analysis.The results show that the system frequency changes in stages with the increase of the stiffness of the integrated composite beam connection.Especially in the case of varying environments,as the temperature increases,the frequency of system will first increase to a certain maximum value and then gradually decrease.Furthermore,the NiTi-ST effectively reduces vibration in the integrated composite beam,particularly under varying temperatures and external excitations.展开更多
In this study,the dosimetric characteristics(thickness applicability,preheating time,temperature and humidity dependence,in-batch uniformity,readout reproducibility,dose linearity,self-decay,and electron energy respon...In this study,the dosimetric characteristics(thickness applicability,preheating time,temperature and humidity dependence,in-batch uniformity,readout reproducibility,dose linearity,self-decay,and electron energy response)of engineered polycarbonate films irradiated with an electron beam(0–600 kGy)were investigated using photoluminescence spectroscopy.The results show a linear relationship between photoluminescence intensity and radiation dose when the thickness of the polycarbonate film is 0.3 mm.A higher fluorescence intensity can be obtained by preheating at 60℃ for 180 min before photoluminescence spectrum analysis.As the temperature during spectral testing and the ambient humidity(during and after irradiation)increased,the photoluminescence intensity of the polycarbonate films decreased.The photoluminescence intensity deviation of the polycarbonate films produced within the same batch at 100 kGy is 2.73%.After ten times of repeated excitations and readouts,the coefficients of variation in photoluminescence intensity are less than 8.6%,and the linear correlation coefficient between photoluminescence intensity and irradiation dose is 0.965 in the dose capture range of 20–600 kGy.Within 60 days of irradiation,the photoluminescence intensity of the polycarbonate film decreased to 60%of the initial value.The response of the 0.3 mm polycarbonate films to electron beams with energies exceeding 3.5 MeV does not differ significantly.This comprehensive analysis indicates the potential of polycarbonate films as a high-radiation dose detection material.展开更多
The spontaneous conversion of muonium to antimuonium is an interesting charged lepton flavor violation phenomenon that offers a sensitive probe for potential new physics and serves as a tool to constrain the parameter...The spontaneous conversion of muonium to antimuonium is an interesting charged lepton flavor violation phenomenon that offers a sensitive probe for potential new physics and serves as a tool to constrain the parameter space beyond the Standard Model.The Muonium-to-Antimuonium Conversion Experiment(MACE)was designed to utilize a high-intensity muon beam,a Michel electron magnetic spectrometer,a positron transport system,and a positron detection system to either discover or constrain this rare process with a conversion probability of O(10^(-13)).This article presents an overview of the theoretical framework and a detailed description of the experimental design for muonium-to-antimuonium conversion.展开更多
With the development of the semiconductor industry below the 7 nm scale,critical dimension small-angle X-ray scattering(CD-SAXS)has emerged as a powerful tool for quantitatively measuring nanoscale deviations.In this ...With the development of the semiconductor industry below the 7 nm scale,critical dimension small-angle X-ray scattering(CD-SAXS)has emerged as a powerful tool for quantitatively measuring nanoscale deviations.In this study,the effects of X-ray beam size and photon energy on the accuracy of critical dimension measurements were investigated.Critical dimensions measured using beams with different spot sizes showed different deviations from the expected values.Beam sizes that were either too large or too small did not improve confidence intervals.As the incident energy increased,the X-ray transmission rate increased,while the scattering cross section decreased,resulting in a gradual decrease in the signal-to-noise ratio of the diffraction peaks,which reduced the accuracy of the CD-SAXS measurements.An optimal accuracy was obtained at 12 keV with a smaller beam size.Using an effective trapezoid model,the results yielded an average pitch of 100.4±0.2 nm,width of 49.8±0.2 nm,height of 130.0±0.2 nm,and a sidewall angle below 1.1°±0.1°.These results provide crucial guidance for the future development of CD-SAXS laboratories and the construction of X-ray machines as well as robust support for research in related fields.展开更多
In a rapid cycling synchrotron(RCS),the magnetic field is synchronized with the beam energy,creating a highly dynamic magnetic environment.A ceramic chamber with a shielding layer(RF shield),composed of a series of co...In a rapid cycling synchrotron(RCS),the magnetic field is synchronized with the beam energy,creating a highly dynamic magnetic environment.A ceramic chamber with a shielding layer(RF shield),composed of a series of copper strips connected to a capacitor at either end,is typically employed as a vacuum chamber to mitigate eddy current effects and beam coupling impedance.Consequently,the ceramic chamber exhibits a thin-walled multilayered complex structure.Previous theoretical studies have suggested that the impedance of such a structure has a negligible impact on the beam.However,recent impedance measurements of the ceramic chamber in the China Spallation Neutron Source(CSNS)RCS revealed a resonance in the low-frequency range,which was confirmed by further theoretical analysis as a source of beam instability in the RCS.Currently,the magnitude of this impedance cannot be accurately assessed using theoretical calculations.In this study,we used the CST Microwave Studio to confirm the impedance of the ceramic chamber.Further simulations covering six different types of ceramic chambers were conducted to develop an impedance model in the RCS.Additionally,this study investigates the resonant characteristics of the ceramic chamber impedance,finding that the resonant frequency is closely related to the capacitance of the capacitors.This finding provides clear directions for further impedance optimization and is crucial for achieving a beam power of 500 kW for the CSNS Phase-Ⅱ project(CSNS-Ⅱ).However,careful attention must be paid to the voltage across the capacitors.展开更多
The microstructural evolution and mechanical properties of a vacuum electron beam welded aerospace 5B70 aluminum alloy joint were studied.Quantitative analyses of the phase composition,microstructural evolution,grain ...The microstructural evolution and mechanical properties of a vacuum electron beam welded aerospace 5B70 aluminum alloy joint were studied.Quantitative analyses of the phase composition,microstructural evolution,grain size,grain boundary density,and texture changes were performed by X-ray diffraction,scanning electron microscopy,and electron backscatter diffraction.The fusion zone(FZ)comprises equiaxed cellular crystals,and a fine~20μm-thick crystal layer forms in the transition zone(TZ)between the FZ and heat affected zone(HAZ).The HAZ closely resembles the base material(BM),retaining the original rolling microstructure.Mechanical property testing shows that the fine-grained layer in the TZ exhibits the highest nanohardness,with the FZ corresponding to the lowest microhardness.The welded-joint sample has lower yield strength,ultimate tensile strength,and elongation after fracture than the BM.These reductions of mechanical properties are primarily influenced by the grain size and distribution of the precipitated phases.展开更多
With the continuous development of the offshore wind industry,the design concept of composite foundation has been given attention in the past decade.This paper presents an accurate method for investigating the horizon...With the continuous development of the offshore wind industry,the design concept of composite foundation has been given attention in the past decade.This paper presents an accurate method for investigating the horizontal vibration of monopile-friction wheel composite foundations in layered saturated soil.Firstly,the three-dimensional continuum mechanics theory with the range of linear elasticity is introduced to calculate the frictional resistance distributed on the upper soil surface.Then,the resistances of multilayered soils and inviscid seawater to the pile shaft under horizontal harmonic excitation are obtained using Novak's plane strain model,Biot's porous media theory and radiationwave theory.Thirdly,the expressions for the deformation,bending moment and internal force of the Euler-Bernoulli pile are derived using the boundary conditions with definitephysical meaning and transfer matrix method.By comparing with the results of 1g laboratory test and the idealized formula reported by the literature,the rationality and accuracy of the developed dynamical model can be verified.Finally,this paper conducts a series of worked examples to investigate the influencesof the elastic modulus and thickness of three-layer saturated soil and the location of interlayer soil on the horizontal dynamic vibration of composite foundation.The results show that an increase in elastic modulus of the surface soil is an effective way to improve the dynamic stability of the composite foundation in service conditions.The conclusions drawn from the numerical examples can develop some guidelines for the current foundation design of offshore wind turbines.展开更多
We develop an ultrafast Yb-fiber laser system based on eight-channel coherent beam combining utilizing commercially available rod-type Yb-fibers.To ensure good combining efficiency and long-term operation of the syste...We develop an ultrafast Yb-fiber laser system based on eight-channel coherent beam combining utilizing commercially available rod-type Yb-fibers.To ensure good combining efficiency and long-term operation of the system at the attosecond laser facility under construction,we fully stabilize the phase,group-delay,and beam-pointing of the eight fiber channels.Especially,we propose a novel multi-step hill climbing method to control both group-delay and beam-pointing.At a repetition rate of 1 MHz,this laser system delivers 270-fs pulses with 1.18-k W average power(1.18-m J pulse energy).The average-power instability of the laser system running for 12 hours is 0.32%.展开更多
Sandwich functionally graded(FG)auxetic beams are extensively utilized in aerospace,automotive,and biomedical industries due to their excellent strength-toweight ratio,impact resistance,and tunable mechanical properti...Sandwich functionally graded(FG)auxetic beams are extensively utilized in aerospace,automotive,and biomedical industries due to their excellent strength-toweight ratio,impact resistance,and tunable mechanical properties.The integration of FG materials with auxetic structures enhances their adaptability in advanced engineering applications.However,understanding their dynamic behavior under external excitations is essential for optimal design and structural reliability.Nonlinear interactions in such structures pose significant challenges in vibration analysis,necessitating robust analytical methods.This study presents a closed-form solution for the nonlinear forced vibration analysis of sandwich FG auxetic beams,offering an accurate and efficient method for predicting their dynamic response.The beam consists of two FG face sheets with material properties varying through the thickness and a re-entrant honeycomb auxetic core with an adjustable Poisson's ratio.The governing nonlinear equations of motion are derived using the first-order shear deformation theory(FSDT),the modified Gibson model,and the von Kármán relations,formulated through Hamilton's principle.A closed-form solution is obtained via the Galerkin method and multiple-scale technique.The results demonstrate that FG layers enable control of the overweight and dynamic response amplitude,with positive power law indexes reducing weight.Comparisons with finite element results confirm the accuracy of the proposed formulation.展开更多
The hybridization gap in strained-layer InAs/In_(x)Ga_(1−x) Sb quantum spin Hall insulators(QSHIs)is significantly enhanced compared to binary InAs/GaSb QSHI structures,where the typical indium composition,x,ranges be...The hybridization gap in strained-layer InAs/In_(x)Ga_(1−x) Sb quantum spin Hall insulators(QSHIs)is significantly enhanced compared to binary InAs/GaSb QSHI structures,where the typical indium composition,x,ranges between 0.2 and 0.4.This enhancement prompts a critical question:to what extent can quantum wells(QWs)be strained while still preserving the fundamental QSHI phase?In this study,we demonstrate the controlled molecular beam epitaxial growth of highly strained-layer QWs with an indium composition of x=0.5.These structures possess a substantial compressive strain within the In_(0.5)Ga_(0.5)Sb QW.Detailed crystal structure analyses confirm the exceptional quality of the resulting epitaxial films,indicating coherent lattice structures and the absence of visible dislocations.Transport measurements further reveal that the QSHI phase in InAs/In_(0.5)Ga_(0.5)Sb QWs is robust and protected by time-reversal symmetry.Notably,the edge states in these systems exhibit giant magnetoresistance when subjected to a modest perpendicular magnetic field.This behavior is in agreement with the𝑍2 topological property predicted by the Bernevig–Hughes–Zhang model,confirming the preservation of topologically protected edge transport in the presence of enhanced bulk strain.展开更多
We Built Railways on the Roof of the World Author:Wang Quanquan Paperback,155 pages Published by Foreign Languages Press The jade-green Fuxing(rejuvenation)bullet train,snow white hada(prayer scarves),and beaming face...We Built Railways on the Roof of the World Author:Wang Quanquan Paperback,155 pages Published by Foreign Languages Press The jade-green Fuxing(rejuvenation)bullet train,snow white hada(prayer scarves),and beaming faces keep flashing into the photographer’s lens.展开更多
Based on the microstructure characterization,electrochemical impedance spectroscopy,potentiodynamic polarization,and immersion corrosion,this work comparatively analyzed the differences in the electrochemical corrosio...Based on the microstructure characterization,electrochemical impedance spectroscopy,potentiodynamic polarization,and immersion corrosion,this work comparatively analyzed the differences in the electrochemical corrosion morphology and post-foil formation surface morphology of laser beam welded(LBW)sample and spin-formed sample,and compared the corrosion resistance and Cu foil formation ability of two samples in H_(2)SO_(4)/NaCl solution and CuSO_(4) reducing electrolyte.Results show that in H_(2)SO_(4) and NaCl solutions,LBW sample and spin-formed sample exhibit excellent passivation ability and corrosion resistance.Both samples show uniform corrosion morphologies and similar corrosion resistance in the strong acidic solution containing Cl^(-).Meanwhile,the Cu foil formation ability of the welded joint is similar to that of the spin-formed sample,and both samples obtain intact Cu foils with high-quality surfaces and small differences in properties.展开更多
基金supported by the Leader Researcher Program(NRF-2019R1A3B2068083)The National Research Facilities and Equipment Center(NFEC)at the Ministry of Science and ICT Support from the supporting project for advancement of leading research facilities(PG2023003-03)the quantum computing technology development program of the Quantum Information Research Support Center,funded through the National research foundation of Korea(2020M3H3A1110365).
文摘Beam shaping in nanophotonic systems remains a challenge due to the reliance on complex heuristic optimization procedures.In this work,we experimentally demonstrate a novel approach to topological beam shaping using Jackiw-Rebbi states in metasurfaces.By fabricating thin-film dielectric structures with engineered Dirac-mass distributions,we create domain walls that allow precise control over beam profiles.We observe the emergence of Jackiw-Rebbi states and confirm their localized characteristics.Notably,we achieve a flat-top beam profile by carefully tailoring the Diracmass distribution,highlighting the potential of this method for customized beam shaping.This experimental realization establishes our approach as a new mechanism for beam control,rooted in topological physics,and offers an efficient strategy for nanophotonic design.
基金National Natural Science Foundation of China(12405168)The Fundamental Research Funds for the Central Universities,China(2024CDJXY004)。
文摘[Background]High harmonic cavities are widely used in electron storage rings to lengthen thebunch,lower the bunch peak current,thereby reducing the IBS effect,enhancing the Touschek lifetime,as well asproviding Landau damping,which is particularly important for storage rings operating with ultra-low emittance or atlow beam energy.[Purpose]To further increase the bunch length without additional hardware costs,the phasemodulation in a dual-RF system is considered.[Methods]In this paper,turn-by-turn simulations incorporating randomsynchrotron radiation excitation are conducted,and a brief analysis is presented to explain the bunch lengtheningmechanism.[Results]Simulation results reveal that the peak current can be further reduced,thereby mitigating IBSeffects and enhancing the Touschek lifetime.Although the energy spread increases,which tends to reduce thebrightness of higher-harmonic radiation from the undulator,the brightness of the fundamental harmonic can,in fact,beimproved.
基金National Natural Science Foundation of China(12125509,11961141003,12275361,U2267205,12175152,12175121)National Key Research and Development Project(2022YFA1602301)Continuous-support Basic Scientific Research Project。
文摘To generate a neutron beam exhibiting a Maxwellian energy distribution with narrow emission angles for measuring the neutron capture reaction rates of the s-process nuclides,a monoenergetic 3.4 MeV proton beam produced by the tandem-accelerator in the China Institute of Atomic Energy was utilized.The proton beam was first transmitted through a 60.5μm aluminum foil and then impinged on a natural LiF target to produce neutron beam via^(7)Li(p,n)7Be reaction.The quasi-Gaussian energy distribution of protons in the LiF target resulted in neutron energy spectra that agreed with a Maxwellian energy distribution at kT=(22±2)keV,which was achieved by integrating neutrons detected within an emission angle of 65.0°±2.6°using a ^(6)Li glass detector positioned at 65°relative to the proton beam direction.The narrow angular spread of the Maxwelliandistributed neutron beam enables direct measurement of neutron capture cross-sections for most s-process nuclides,overcoming previous experimental limitations associated with broad angular distributions.
基金financially supported by the National Key Research and Development Program of China(Grant No.2021YFA1400403)the National Natural Science Foundation of China(Grant Nos.12374183,92165205)+2 种基金the Natural Science Foundation of Jiangsu Province(Grant No.BK20233001)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)the Fundamental Research Funds for the Central Universities(Grant No.020414380207).
文摘Interplay between topology and magnetism can give rise to exotic properties in topological materials.Two-dimensional bismuth has been extensively studied owing to its topological states with a strong spin-orbit coupling,and 1T-VTe_(2)monolayer theoretically predicted to host an intrinsic magnetism as experimentally suggested.In this work,we successfully constructed a vertical heterostructure composed of the two-dimensional Bi(110)monolayer and 1T-VTe_(2)monolayer by using molecular beam epitaxy(MBE).Scanning tunneling microscopy(STM)measurements revealed that the growth of Bi preferably occurs along the step edges of the VTe_(2)monolayer,forming a Bi(110)monolayer on top of the VTe_(2)monolayer next to a peripheral Bi bilayer.The Bi(100)/VTe_(2)heterostructure exhibits a specific lattice registry with a well-defined moiréperiodicity.Scanning tunneling spectroscopy(STS)measurements further unveiled an universal suppression in the local density-of-states at the boundary of the Bi(110)/VTe_(2)bilayer.By examining the atomic structures of Bi(110)boundaries,we found this effect does not originate from the previously proposed atomic reconstruction at the step edge of Bi(110),but is likely related to the magnetic properties of the VTe_(2)monolayer.
基金supported by the Beijing Natural Science Foundation under Grant L253002.
文摘For 5G millimeter wave(mm-Wave)user equipments(UEs),all test cases must be evaluated in Over-The-Air(OTA)manner.Test time increases dramatically compared to Sub-6 GHz.Therefore,test time reduction is of great significance for 5G mm-Wave OTA testing.Among all test cases,beam peak search is the most time-consuming,taking up the majority of the overall test time.Therefore,the objective of this work is to determine a suitable beam peak search grid for 5G mm-Wave UEs with satisfactory accuracy and efficiency.Through radiation property investigation of 5G mm-Wave commercial UEs,more reasonable reference array configuration(4×2)and reference deployment scenario(composite beam)are proposed for beam peak search grid analysis.The effect of different grid configurations on beam peak search precision are characterized quantitatively.The determination of associated measurement uncertainty(MU)term along with quantitative analysis approach are proposed based on statistical analysis.Finally,the recommended minimum number of beam peak search grid points is 182 based on the proposed 4×2 array under composite beam scenario.Compared with currently-required 1106 points in 3GPP/CTIA specifications,over 80%reduction can be achieved without increasing the MU limit.The feasibility of the proposed MU analysis as well as the recommended grids is demonstrated through measurements.
基金supported by the Hundred-person Program of Chinese Academy of Sciences and the National Natural Science Foundation of China(No.11905074).
文摘Electron beam injectors are pivotal components of large-scale scientific instruments,such as synchrotron radiation sources,free-electron lasers,and electron-positron colliders.The quality of the electron beam produced by the injector critically influences the performance of the entire accelerator-based scientific research apparatus.The injectors of such facilities usually use photocathode and thermionic-cathode electron guns.Although the photocathode injector can produce electron beams of excellent quality,its associated laser system is massive and intricate.The thermionic-cathode electron gun,especially the gridded electron gun injector,has a simple structure capable of generating numerous electron beams.However,its emittance is typically high.In this study,methods to reduce beam emittance are explored through a comprehensive analysis of various grid structures and preliminary design results,examining the evolution of beam phase space at different grid positions.An optimization method for reducing the emittance of a gridded thermionic-cathode electron gun is proposed through theoretical derivation,electromagnetic-field simulation,and beam-dynamics simulation.A 50%reduction in emittance was achieved for a 50 keV,1.7 A electron gun,laying the foundation for the subsequent design of a high-current,low-emittance injector.
基金supported by the National Natural Science Foundation of China(Grant Nos.11804348,11775056,11975154,12225505,and 12405281)the Science Challenge(Project No.TZ2018005)+2 种基金supported by the Shanghai Pujiang Program(Grant No.23PJ1414600)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0890203)supported by the Accelerator Technology Helmholtz Infrastructure consortium ATHENA.
文摘The effects of initial spin orientation on the final electron beam polarization in laser wakefield acceleration in a pre-polarized plasma are investigated theoretically and numerically.From the results of variation of the initial spin direction,the spin dynamics of the electron beam are found to depend on the self-injection mechanism.The effects of wakefields and laser fields are studied using test particle dynamics and particle-in-cell simulations based on the Thomas-Bargmann-Michel-Telegdi equation.Compared with transverse injection,longitudinal injection is found to be preferable for obtaining a highly polarized electron beam.
基金supported by the National Natural Science Foundation of China(No.12272240)the Liaoning Revitalization Talents Program,China(No.XLYC2203197)。
文摘Traditional dynamic analysis of mechanical structures,often limited to individual beams or plates,fails to fully capture their dynamic behaviors.In systems where space and mass are constrained,such as the battery support structures in electric aircraft,conventional absorbers and isolators are insufficient for effective vibration control.This study simplifies the battery support structure of electric aircraft as an integrated composite beam consisting of three interconnected beams,and investigated its structural dynamics properties and nonlinear vibration control under thermal conditions caused by battery heat.The nonlinear vibration control is performed using the Nitinol steel wire ropes(Ni Ti-ST),with nonlinear damping properties.The natural frequencies of system are determined using the Rayleigh-Ritz technique.Theoretical results are validated through both Finite Element Method(FEM)and hammer tests.Moreover,the dynamic equations are derived using the Lagrange method and discretized via the Galerkin Truncation Method(GTM).The Harmonic Balance Method(HBM)is used to evaluate the vibration responses of the integrated model,with further verification through the Runge-Kutta Method(RKM).The experiments are conducted to corroborate the theoretical analysis.The results show that the system frequency changes in stages with the increase of the stiffness of the integrated composite beam connection.Especially in the case of varying environments,as the temperature increases,the frequency of system will first increase to a certain maximum value and then gradually decrease.Furthermore,the NiTi-ST effectively reduces vibration in the integrated composite beam,particularly under varying temperatures and external excitations.
基金supported by the National Natural Science Foundation of China(No.12305385)Key Projects of Scientific Research of the Hunan Provincial Department of Education(22A0310)the Research Startup Project of University of South China(220XQD025).
文摘In this study,the dosimetric characteristics(thickness applicability,preheating time,temperature and humidity dependence,in-batch uniformity,readout reproducibility,dose linearity,self-decay,and electron energy response)of engineered polycarbonate films irradiated with an electron beam(0–600 kGy)were investigated using photoluminescence spectroscopy.The results show a linear relationship between photoluminescence intensity and radiation dose when the thickness of the polycarbonate film is 0.3 mm.A higher fluorescence intensity can be obtained by preheating at 60℃ for 180 min before photoluminescence spectrum analysis.As the temperature during spectral testing and the ambient humidity(during and after irradiation)increased,the photoluminescence intensity of the polycarbonate films decreased.The photoluminescence intensity deviation of the polycarbonate films produced within the same batch at 100 kGy is 2.73%.After ten times of repeated excitations and readouts,the coefficients of variation in photoluminescence intensity are less than 8.6%,and the linear correlation coefficient between photoluminescence intensity and irradiation dose is 0.965 in the dose capture range of 20–600 kGy.Within 60 days of irradiation,the photoluminescence intensity of the polycarbonate film decreased to 60%of the initial value.The response of the 0.3 mm polycarbonate films to electron beams with energies exceeding 3.5 MeV does not differ significantly.This comprehensive analysis indicates the potential of polycarbonate films as a high-radiation dose detection material.
基金supported by National Natural Science Foundation of China(Nos.12075326,11535014,11975017,12475191,11905092,12105132 and 12175039)Guangdong Basic and Applied Basic Research Foundation(No.2025A1515010669)+7 种基金Natural Science Foundation of Guangzhou(No.2024A04J6243)Fundamental Research Funds for the Central Universities(23xkjc017)in Sun Yat-sen UniversityBasic Research Conditions and Major Scientific Instrument and Equipment Research and Development Projects of the Ministry of Science and Technology(No.2022YFF0705602)the State Key Laboratory of Particle Detection and Electronics(SKLPDE-ZZ-202412)Natural Science Foundation of Shandong Province(No.2023HWYQ-010)the“Fundamental Research Funds for the Central Universities”at Southeast Universitythe National Development and Reform Commission of China(Large Research Infrastructures of 12th Five-Year Plan:China initiative Accelerator Driven System)(No.2017-000052-75-01-000590)Innovation Training Program for bachelor students in Sun Yat-sen University。
文摘The spontaneous conversion of muonium to antimuonium is an interesting charged lepton flavor violation phenomenon that offers a sensitive probe for potential new physics and serves as a tool to constrain the parameter space beyond the Standard Model.The Muonium-to-Antimuonium Conversion Experiment(MACE)was designed to utilize a high-intensity muon beam,a Michel electron magnetic spectrometer,a positron transport system,and a positron detection system to either discover or constrain this rare process with a conversion probability of O(10^(-13)).This article presents an overview of the theoretical framework and a detailed description of the experimental design for muonium-to-antimuonium conversion.
基金supported by the National Natural Science Foundation of China(No.12175295)the National Key R&D Program of China(2021YFA1601000)the Shanghai Municipal Science and Technology Major Project。
文摘With the development of the semiconductor industry below the 7 nm scale,critical dimension small-angle X-ray scattering(CD-SAXS)has emerged as a powerful tool for quantitatively measuring nanoscale deviations.In this study,the effects of X-ray beam size and photon energy on the accuracy of critical dimension measurements were investigated.Critical dimensions measured using beams with different spot sizes showed different deviations from the expected values.Beam sizes that were either too large or too small did not improve confidence intervals.As the incident energy increased,the X-ray transmission rate increased,while the scattering cross section decreased,resulting in a gradual decrease in the signal-to-noise ratio of the diffraction peaks,which reduced the accuracy of the CD-SAXS measurements.An optimal accuracy was obtained at 12 keV with a smaller beam size.Using an effective trapezoid model,the results yielded an average pitch of 100.4±0.2 nm,width of 49.8±0.2 nm,height of 130.0±0.2 nm,and a sidewall angle below 1.1°±0.1°.These results provide crucial guidance for the future development of CD-SAXS laboratories and the construction of X-ray machines as well as robust support for research in related fields.
基金supported by the Guangdong Basic and Applied Basic Research Foundation,China(No.2021B1515140007).
文摘In a rapid cycling synchrotron(RCS),the magnetic field is synchronized with the beam energy,creating a highly dynamic magnetic environment.A ceramic chamber with a shielding layer(RF shield),composed of a series of copper strips connected to a capacitor at either end,is typically employed as a vacuum chamber to mitigate eddy current effects and beam coupling impedance.Consequently,the ceramic chamber exhibits a thin-walled multilayered complex structure.Previous theoretical studies have suggested that the impedance of such a structure has a negligible impact on the beam.However,recent impedance measurements of the ceramic chamber in the China Spallation Neutron Source(CSNS)RCS revealed a resonance in the low-frequency range,which was confirmed by further theoretical analysis as a source of beam instability in the RCS.Currently,the magnitude of this impedance cannot be accurately assessed using theoretical calculations.In this study,we used the CST Microwave Studio to confirm the impedance of the ceramic chamber.Further simulations covering six different types of ceramic chambers were conducted to develop an impedance model in the RCS.Additionally,this study investigates the resonant characteristics of the ceramic chamber impedance,finding that the resonant frequency is closely related to the capacitance of the capacitors.This finding provides clear directions for further impedance optimization and is crucial for achieving a beam power of 500 kW for the CSNS Phase-Ⅱ project(CSNS-Ⅱ).However,careful attention must be paid to the voltage across the capacitors.
基金supported by the National Natural Science Foundation of China(Nos.52175206,52205187,52130509)the Science and Technology Planning Project of Guizhou Province,China(No.ZK[2022]013)。
文摘The microstructural evolution and mechanical properties of a vacuum electron beam welded aerospace 5B70 aluminum alloy joint were studied.Quantitative analyses of the phase composition,microstructural evolution,grain size,grain boundary density,and texture changes were performed by X-ray diffraction,scanning electron microscopy,and electron backscatter diffraction.The fusion zone(FZ)comprises equiaxed cellular crystals,and a fine~20μm-thick crystal layer forms in the transition zone(TZ)between the FZ and heat affected zone(HAZ).The HAZ closely resembles the base material(BM),retaining the original rolling microstructure.Mechanical property testing shows that the fine-grained layer in the TZ exhibits the highest nanohardness,with the FZ corresponding to the lowest microhardness.The welded-joint sample has lower yield strength,ultimate tensile strength,and elongation after fracture than the BM.These reductions of mechanical properties are primarily influenced by the grain size and distribution of the precipitated phases.
基金supported by the National Natural Science Foundation of China(Grant No.52178329),the China Scholarship Council(Grant No.202306130155)the Postgraduate Scientific Research Innovation Project of Hunan Province,China(Grant No.CX20230442).
文摘With the continuous development of the offshore wind industry,the design concept of composite foundation has been given attention in the past decade.This paper presents an accurate method for investigating the horizontal vibration of monopile-friction wheel composite foundations in layered saturated soil.Firstly,the three-dimensional continuum mechanics theory with the range of linear elasticity is introduced to calculate the frictional resistance distributed on the upper soil surface.Then,the resistances of multilayered soils and inviscid seawater to the pile shaft under horizontal harmonic excitation are obtained using Novak's plane strain model,Biot's porous media theory and radiationwave theory.Thirdly,the expressions for the deformation,bending moment and internal force of the Euler-Bernoulli pile are derived using the boundary conditions with definitephysical meaning and transfer matrix method.By comparing with the results of 1g laboratory test and the idealized formula reported by the literature,the rationality and accuracy of the developed dynamical model can be verified.Finally,this paper conducts a series of worked examples to investigate the influencesof the elastic modulus and thickness of three-layer saturated soil and the location of interlayer soil on the horizontal dynamic vibration of composite foundation.The results show that an increase in elastic modulus of the surface soil is an effective way to improve the dynamic stability of the composite foundation in service conditions.The conclusions drawn from the numerical examples can develop some guidelines for the current foundation design of offshore wind turbines.
基金Project supported by the Key Deployment Special Research Project of the Chinese Academy of Sciences(Grant No.PTYQ2022YZ0001)the National Natural Science Foundation of China(Grant Nos.62175255 and 62227822)the National Key Research and Development Program of China(Grant No.2021YFB3602602)。
文摘We develop an ultrafast Yb-fiber laser system based on eight-channel coherent beam combining utilizing commercially available rod-type Yb-fibers.To ensure good combining efficiency and long-term operation of the system at the attosecond laser facility under construction,we fully stabilize the phase,group-delay,and beam-pointing of the eight fiber channels.Especially,we propose a novel multi-step hill climbing method to control both group-delay and beam-pointing.At a repetition rate of 1 MHz,this laser system delivers 270-fs pulses with 1.18-k W average power(1.18-m J pulse energy).The average-power instability of the laser system running for 12 hours is 0.32%.
文摘Sandwich functionally graded(FG)auxetic beams are extensively utilized in aerospace,automotive,and biomedical industries due to their excellent strength-toweight ratio,impact resistance,and tunable mechanical properties.The integration of FG materials with auxetic structures enhances their adaptability in advanced engineering applications.However,understanding their dynamic behavior under external excitations is essential for optimal design and structural reliability.Nonlinear interactions in such structures pose significant challenges in vibration analysis,necessitating robust analytical methods.This study presents a closed-form solution for the nonlinear forced vibration analysis of sandwich FG auxetic beams,offering an accurate and efficient method for predicting their dynamic response.The beam consists of two FG face sheets with material properties varying through the thickness and a re-entrant honeycomb auxetic core with an adjustable Poisson's ratio.The governing nonlinear equations of motion are derived using the first-order shear deformation theory(FSDT),the modified Gibson model,and the von Kármán relations,formulated through Hamilton's principle.A closed-form solution is obtained via the Galerkin method and multiple-scale technique.The results demonstrate that FG layers enable control of the overweight and dynamic response amplitude,with positive power law indexes reducing weight.Comparisons with finite element results confirm the accuracy of the proposed formulation.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant Nos.XDB28000000 and XDB0460000)the Quantum Science and Technology-National Science and Technology Major Project (Grant No.2021ZD0302600)the National Key Research and Development Program of China(Grant No.2024YFA1409002)。
文摘The hybridization gap in strained-layer InAs/In_(x)Ga_(1−x) Sb quantum spin Hall insulators(QSHIs)is significantly enhanced compared to binary InAs/GaSb QSHI structures,where the typical indium composition,x,ranges between 0.2 and 0.4.This enhancement prompts a critical question:to what extent can quantum wells(QWs)be strained while still preserving the fundamental QSHI phase?In this study,we demonstrate the controlled molecular beam epitaxial growth of highly strained-layer QWs with an indium composition of x=0.5.These structures possess a substantial compressive strain within the In_(0.5)Ga_(0.5)Sb QW.Detailed crystal structure analyses confirm the exceptional quality of the resulting epitaxial films,indicating coherent lattice structures and the absence of visible dislocations.Transport measurements further reveal that the QSHI phase in InAs/In_(0.5)Ga_(0.5)Sb QWs is robust and protected by time-reversal symmetry.Notably,the edge states in these systems exhibit giant magnetoresistance when subjected to a modest perpendicular magnetic field.This behavior is in agreement with the𝑍2 topological property predicted by the Bernevig–Hughes–Zhang model,confirming the preservation of topologically protected edge transport in the presence of enhanced bulk strain.
文摘We Built Railways on the Roof of the World Author:Wang Quanquan Paperback,155 pages Published by Foreign Languages Press The jade-green Fuxing(rejuvenation)bullet train,snow white hada(prayer scarves),and beaming faces keep flashing into the photographer’s lens.
基金Key Research and Development Program of Shaanxi Province(2022GY-410)Funding of Western Titanium Technologies Co.,Ltd(WX2210)。
文摘Based on the microstructure characterization,electrochemical impedance spectroscopy,potentiodynamic polarization,and immersion corrosion,this work comparatively analyzed the differences in the electrochemical corrosion morphology and post-foil formation surface morphology of laser beam welded(LBW)sample and spin-formed sample,and compared the corrosion resistance and Cu foil formation ability of two samples in H_(2)SO_(4)/NaCl solution and CuSO_(4) reducing electrolyte.Results show that in H_(2)SO_(4) and NaCl solutions,LBW sample and spin-formed sample exhibit excellent passivation ability and corrosion resistance.Both samples show uniform corrosion morphologies and similar corrosion resistance in the strong acidic solution containing Cl^(-).Meanwhile,the Cu foil formation ability of the welded joint is similar to that of the spin-formed sample,and both samples obtain intact Cu foils with high-quality surfaces and small differences in properties.
