This paper proposes a method to generate Bessel-like collimated beams with suppressed side lobes using the flexural vibration modes of a fixed boundary circular plate,which is excited by a longitudinally vibrating tra...This paper proposes a method to generate Bessel-like collimated beams with suppressed side lobes using the flexural vibration modes of a fixed boundary circular plate,which is excited by a longitudinally vibrating transducer in a ring excitation manner.The factors affecting the generation of Bessel-like collimated beams are investigated by theoretical analysis,numerical simulation and experimental methods.The results indicate that Bessel-like wave can be generated by a thin circular plate with fixed boundaries.The third-order mode of the circular plate can be modified to generate a collimated beam with suppressing side lobes when it is excited in a ring excitation manner and the excitation position lies between the first two nodal circles of the plate.As the excitation radius increases,the main lobe width of the resulting Bessel-like collimated beam decreases,the extent of the focusing region increases,and the amplitude of the side lobes initially increases and then decreases.Based on the simulation results,a prototype Bessel-like collimated beam generation system is made and measured experimentally.The experimental results are in good agreement with the numerical results.The Bessel-like collimated beam can be generated by the proposed system,which has potential application in the fields of long-range detection,imaging of highly attenuated materials,and airflow acceleration.展开更多
In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3A...In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3Al/ Nb3Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly fiat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb3Al/Nb3Sn fits more to the ＂Flat/steep＂ band model than to the van-Hove singularity scenario. The fiat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.展开更多
In practical engineering structures,complex low-frequency vibrations are often encountered.However,most reported elastic metamaterials are designed for high-frequency ranges or rely on substantial additional mass to c...In practical engineering structures,complex low-frequency vibrations are often encountered.However,most reported elastic metamaterials are designed for high-frequency ranges or rely on substantial additional mass to control low-frequency vibrations,making them difficult to apply in real-world engineering scenarios.To address this limitation,we propose a homogeneous locally resonance metamaterial with tunable low-frequency bandgaps.This design overcomes the challenges associated with conventional local resonators,which are often large and heavy,making them impractical for engineering applications.By integrating resonator structures composed of elastic chiral spiral beams and mass blocks onto the supporting structure,we achieve lowfrequency vibration control within limited spaces,broadband absorption with gradient parameter units,and vibration control under different curvatures.The effectiveness of the proposed design is validated through comparative computational methods,dispersion curve calculations,frequency response simulations,and experimental tests.This study proposes a novel LRM structure with a full bandgap from 96.9 to 124 Hz.The transmittance is negative in most of the band gap range,which has been verified through numerical and experimental results.This approach effectively meets the complex low-frequency vibration control requirements of various curved structures in engineering applications,providing a viable solution for low-frequency vibration control of structures such as flat and cylindrical shells.展开更多
This work proposes a new simulation algorithm to improve message handling in discrete event formalism. We present an approach to minimize simulation execution time. To do this, we propose to reduce the number of excha...This work proposes a new simulation algorithm to improve message handling in discrete event formalism. We present an approach to minimize simulation execution time. To do this, we propose to reduce the number of exchanged messages between Parallel DEVS (PDEVS) components (simulators and coordinators). We propose three changes from PDEVS: direct coupling, flat structure and local schedule. The goal is the decentralisation of a number of tasks to make the simulators more autonomous and simplify the coordinators to achieve a greater speedup. We propose to compare the simulation results of several models to demonstrate the benefits of our approach.展开更多
Multipactor and low-pressure gas discharges have a negative impact on the performance and security of microwave components in space.In this manuscript,a 2-dimensional parallel flat plate structural model was designed ...Multipactor and low-pressure gas discharges have a negative impact on the performance and security of microwave components in space.In this manuscript,a 2-dimensional parallel flat plate structural model was designed to simulate the breakdown of multipactor to low-pressure gas discharges.The breakdown levels in the pressure range of 0.1 to 100 torr were verified under the conditions of the Ag material,4-mm gap,2.6-GHz frequency,and air as the background gas.Random secondary electron emission and gas molecule collision processes are incorporated,and the effect of their transition section is studied using trajectory tracking and Monte Carlo methods.A comparison of the model to the available experimental data demonstrates the model’s accuracy.On this basis,the variation of gas adsorption in relation to the surface secondary electron yields was considered,and the effect of the gas adsorption issues on breakdown level was calculated by means of numerical simulations based on some assumptions.The calculation reveals that in a finite volume of space,smaller desorption volumes cause negligible pressure changes,but the secondary electron emission capacity of the material decreases,which,in turn,leads to a flat or rising breakdown level.On the contrary,the larger the desorption volume,the more the gas is collisionally ionized and the breakdown level decreases.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.12474440).
文摘This paper proposes a method to generate Bessel-like collimated beams with suppressed side lobes using the flexural vibration modes of a fixed boundary circular plate,which is excited by a longitudinally vibrating transducer in a ring excitation manner.The factors affecting the generation of Bessel-like collimated beams are investigated by theoretical analysis,numerical simulation and experimental methods.The results indicate that Bessel-like wave can be generated by a thin circular plate with fixed boundaries.The third-order mode of the circular plate can be modified to generate a collimated beam with suppressing side lobes when it is excited in a ring excitation manner and the excitation position lies between the first two nodal circles of the plate.As the excitation radius increases,the main lobe width of the resulting Bessel-like collimated beam decreases,the extent of the focusing region increases,and the amplitude of the side lobes initially increases and then decreases.Based on the simulation results,a prototype Bessel-like collimated beam generation system is made and measured experimentally.The experimental results are in good agreement with the numerical results.The Bessel-like collimated beam can be generated by the proposed system,which has potential application in the fields of long-range detection,imaging of highly attenuated materials,and airflow acceleration.
基金financially supported by the Science Foundation for International Cooperation of Sichuan Province (2014HH0016)the Fundamental Research Funds for the Central Universities (SWJTU2014: A0920502051113-10000)National Magnetic Confinement Fusion Science Program (2011GB112001)
文摘In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3Al/ Nb3Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly fiat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb3Al/Nb3Sn fits more to the ＂Flat/steep＂ band model than to the van-Hove singularity scenario. The fiat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.
基金supported by the National Key Research and Development Plan of China(Grant No.2023YFB3406302)the National Natural Science Foundation of China(Grant No.52175120)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2024A1515011126)。
文摘In practical engineering structures,complex low-frequency vibrations are often encountered.However,most reported elastic metamaterials are designed for high-frequency ranges or rely on substantial additional mass to control low-frequency vibrations,making them difficult to apply in real-world engineering scenarios.To address this limitation,we propose a homogeneous locally resonance metamaterial with tunable low-frequency bandgaps.This design overcomes the challenges associated with conventional local resonators,which are often large and heavy,making them impractical for engineering applications.By integrating resonator structures composed of elastic chiral spiral beams and mass blocks onto the supporting structure,we achieve lowfrequency vibration control within limited spaces,broadband absorption with gradient parameter units,and vibration control under different curvatures.The effectiveness of the proposed design is validated through comparative computational methods,dispersion curve calculations,frequency response simulations,and experimental tests.This study proposes a novel LRM structure with a full bandgap from 96.9 to 124 Hz.The transmittance is negative in most of the band gap range,which has been verified through numerical and experimental results.This approach effectively meets the complex low-frequency vibration control requirements of various curved structures in engineering applications,providing a viable solution for low-frequency vibration control of structures such as flat and cylindrical shells.
文摘This work proposes a new simulation algorithm to improve message handling in discrete event formalism. We present an approach to minimize simulation execution time. To do this, we propose to reduce the number of exchanged messages between Parallel DEVS (PDEVS) components (simulators and coordinators). We propose three changes from PDEVS: direct coupling, flat structure and local schedule. The goal is the decentralisation of a number of tasks to make the simulators more autonomous and simplify the coordinators to achieve a greater speedup. We propose to compare the simulation results of several models to demonstrate the benefits of our approach.
基金substantially supported by the National Natural Science Foundation of China(grant nos.61901361 and 51827809).
文摘Multipactor and low-pressure gas discharges have a negative impact on the performance and security of microwave components in space.In this manuscript,a 2-dimensional parallel flat plate structural model was designed to simulate the breakdown of multipactor to low-pressure gas discharges.The breakdown levels in the pressure range of 0.1 to 100 torr were verified under the conditions of the Ag material,4-mm gap,2.6-GHz frequency,and air as the background gas.Random secondary electron emission and gas molecule collision processes are incorporated,and the effect of their transition section is studied using trajectory tracking and Monte Carlo methods.A comparison of the model to the available experimental data demonstrates the model’s accuracy.On this basis,the variation of gas adsorption in relation to the surface secondary electron yields was considered,and the effect of the gas adsorption issues on breakdown level was calculated by means of numerical simulations based on some assumptions.The calculation reveals that in a finite volume of space,smaller desorption volumes cause negligible pressure changes,but the secondary electron emission capacity of the material decreases,which,in turn,leads to a flat or rising breakdown level.On the contrary,the larger the desorption volume,the more the gas is collisionally ionized and the breakdown level decreases.
