Real time digital recording and numerical reconstruction of a temporal digital hologram sequence have become feasible in recent years.They provide a new measurement method which enjoys the valuable advantages of being...Real time digital recording and numerical reconstruction of a temporal digital hologram sequence have become feasible in recent years.They provide a new measurement method which enjoys the valuable advantages of being full-field,noncontact and high precision.In this paper,a combined method of temporal digital hologram sequence and windowed Fourier transform is proposed to measure the kinematic parameters of random vibration.A series of holograms are recorded by CCD camera and the original phase can be reconstructed by Fresnel reconstruction algorithm.The three-dimensional windowed Fourier transform is used to filter noise in phase and extract the instantaneous kinematic parameters of the specimen,such as the displacement,velocity and acceleration.An experiment is conducted on a chloroprene rubber latex membrane.Results demonstrate that the proposed method determines the vibration parameters precisely and enjoys many merits.展开更多
In the practical measurement of signal to noise ratio(SNR)of analog-to-digital converters(ADCs)by using fast Fourier transformation(FFT)method,the non-coherent sampling is inevitable,leading to spectral leakage which ...In the practical measurement of signal to noise ratio(SNR)of analog-to-digital converters(ADCs)by using fast Fourier transformation(FFT)method,the non-coherent sampling is inevitable,leading to spectral leakage which in turn affects the calculation accuracy and final measurement results.In this paper,a new method based on the Blackman-Harris windowed triple-spectrum-line interpolation is presented for the measurement of ADCs SNR by FFT.The simulation platform is built based on MATLAB and the behavioral dynamic models of the high-speed ADC products of Analog Devices Inc.(ADI)are simulated.The simulation results show that,even in the case of the maximum non-coherent degree,the SNR error is less than0.23dB and reaches the testing standards provided by ADI,confirming that the proposed method is effective for suppressing the spectral leakage effects and improving the SNR test accuracy.展开更多
Let g（x） ∈L<sup>2</sup>（R） and （ω） be the Fourier transform of g（x）.Define g<sub>mn</sub>（x）=e<sup>imx</sup>g（x- 2πn）.In this paper we shall give a sufficient and nec...Let g（x） ∈L<sup>2</sup>（R） and （ω） be the Fourier transform of g（x）.Define g<sub>mn</sub>（x）=e<sup>imx</sup>g（x- 2πn）.In this paper we shall give a sufficient and necessary condition under which {g<sub>mn</sub>（x）} constitutes an orthonormal basis of L<sup>2</sup>（R） for compactly supported g（x） or （ω）.展开更多
Two viologen derivatives containing fluorine substituent(F)with an asymmetric structures,1,1'-bis(4-(trifluoromethyl)phenyl)-[4,4'-bipyridine]dihexafluorophosphate(DFPV)and 1-benzyl-1'-(4-(trifluoromethyl)...Two viologen derivatives containing fluorine substituent(F)with an asymmetric structures,1,1'-bis(4-(trifluoromethyl)phenyl)-[4,4'-bipyridine]dihexafluorophosphate(DFPV)and 1-benzyl-1'-(4-(trifluoromethyl)phenyl)-[4,4'-bipyridine]di-hexafluorophosphate(Bn-FPV),were synthesized.These viologen derivatives as active materials were used to assemble both flexible and rigid electrochromic devices(ECDs).ECDs based on DFPV exhibited reversible color change from colorless to deep green and ECDs based on Bn-FPV exhibited reversible color change from colorless to blue-green within applied voltage.It was found that the devices based on DFPV showed cycle stability,which could still maintain more than 90% after 1000 cycles.In addition,the modulation rate of the device to the solar irradiance is also calculated to characterize its application potential in smart windows.Among them,the rigid device(R-DFPV)based on the DFPV has a large solar irradiance modulation rate of 54.66%,which has the potential to be used as smart windows.展开更多
Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining...Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining technique that overcomes these issues by using impact to create strong bonds without melting the substrate materials.This study investigates the weldability of aluminum alloy Al-5754 with Al-7075 and MARS 380 steel,used in armouring solutions of defense systems,by the use of MPW.In this work,weldability windows are investigated by varying standoff distances between the coating material and its substrate(0.25-4.5 mm)and discharge energies(5-13 kJ)with both O-shape and U-shape inductors.Mechanical strength of the welded joints were assessed through single lap shear tests,identifying optimal welding parameters.Then,the velocity profiles of the flyer plates were measured using heterodyne velocimetry to understand the dynamics of the impact.Then,substructures assembled with the optimal welding conditions were subjected to ballistic testing using 7.62 mm×51 mm NATO and 9 mm×19 mm Parabellum munitions to evaluate the resilience of the welds under ballistic impact.The outcomes demonstrate that MPW effectively joins Al-5754 with both Al-7075 and MARS 380,producing robust welds capable of withstanding ballistic impacts under certain conditions.This research advances the application of MPW in lightweight ballistic protection of defense systems,contributing to the development of more resilient and lighter protective structures.展开更多
Ag-Cu-In-Ti low-temperature filler was used to braze the diamond and copper,and the effects of brazing temperature and soaking time on the microstructure and mechanical properties of the joints were investigated.In ad...Ag-Cu-In-Ti low-temperature filler was used to braze the diamond and copper,and the effects of brazing temperature and soaking time on the microstructure and mechanical properties of the joints were investigated.In addition,the joint formation mechanism was discussed,and the correlation between joint microstructure and mechanical performance was established.Results show that adding appropriate amount of In into the filler can significantly reduce the filler melting point and enhance the wettability of filler on diamond.When the brazing temperature is 750°C and the soaking time is 10 min,a uniformly dense braze seam with excellent metallurgical bonding can be obtained,and its average joint shear strength reaches 322 MPa.The lower brazing temperature can mitigate the risk of diamond graphitization and also reduce the residual stresses during joining.展开更多
针对现有任意反射面速度干涉仪(velocity interferometer system for any reflector,VISAR)装置中依靠人工准直光路的现状,同时为满足未来对远程自动化控制的需求,提出一种新的光路自动准直的方法。该方法通过互补金属氧化物半导体(comp...针对现有任意反射面速度干涉仪(velocity interferometer system for any reflector,VISAR)装置中依靠人工准直光路的现状,同时为满足未来对远程自动化控制的需求,提出一种新的光路自动准直的方法。该方法通过互补金属氧化物半导体(complementary metal oxide semiconductor,CMOS)间接测量并以光斑的像素偏差为系统输入,通过系数矩阵转换和离散模糊反馈控制方法快速消除误差。基于Windows的控制和自动化技术(the Windows control and automation technology,TwinCAT)中视觉和运动等模块,将各模块分别运行在不同的实时内核中,消除了视觉与运动控制模块间的通信环节,实现了快速实时的闭环控制。经过冲击波速度测量实验验证,该系统实现了远程“一键式”自动准直,可将准直时间缩短到2 s,准直精度为4.5μm,解决了现有装置人工调节效率不高的问题,提高了系统的精度和稳定性。展开更多
The environment of low-altitude urban airspace is complex and variable due to numerous obstacles,non-cooperative aircraft,and birds.Unmanned Aerial Vehicles(UAVs)leveraging environmental information to achieve three-d...The environment of low-altitude urban airspace is complex and variable due to numerous obstacles,non-cooperative aircraft,and birds.Unmanned Aerial Vehicles(UAVs)leveraging environmental information to achieve three-dimension collision-free trajectory planning is the prerequisite to ensure airspace security.However,the timely information of surrounding situation is difficult to acquire by UAVs,which further brings security risks.As a mature technology leveraged in traditional civil aviation,the Automatic Dependent Surveillance-Broadcast(ADS-B)realizes continuous surveillance of the information of aircraft.Consequently,we leverage ADS-B for surveillance and information broadcasting,and divide the aerial airspace into multiple sub-airspaces to improve flight safety in UAV trajectory planning.In detail,we propose the secure Sub-airSpaces Planning(SSP)algorithm and Particle Swarm Optimization Rapidly-exploring Random Trees(PSO-RRT)algorithm for the UAV trajectory planning in law-altitude airspace.The performance of the proposed algorithm is verified by simulations and the results show that SSP reduces both the maximum number of UAVs in the sub-airspace and the length of the trajectory,and PSO-RRT reduces the cost of UAV trajectory in the sub-airspace.展开更多
Transparent materials utilized as underwater optical windows are highly vulnerable to various forms of pollution or abrasion due to their intrinsic hydrophilic properties.This susceptibility is particularly pronounced...Transparent materials utilized as underwater optical windows are highly vulnerable to various forms of pollution or abrasion due to their intrinsic hydrophilic properties.This susceptibility is particularly pronounced in underwater environments where pollutants can impede the operation of these optical devices,significantly degrading or even compromising their optical properties.The glass catfish,known for its remarkable transparency in water,maintains surface cleanliness and clarity despite exposure to contaminants,impurities abrasion,and hydraulic pressure.Inspired by the glass catfish’s natural attributes,this study introduces a new solution named subaquatic abrasion-resistant and anti-fouling window(SAAW).Utilizing femtosecond laser ablation and electrodeposition,the SAAW is engineered by embedding fine metal bone structures into a transparent substrate and anti-fouling sliding layer,akin to the sturdy bones among catfish’s body.This approach significantly bolsters the window’s abrasion resistance and anti-fouling performance while maintaining high light transmittance.The sliding layer on the SAAW’s surface remarkably reduces the friction of various liquids,which is the reason that SAAW owns the great anti-fouling property.The SAAW demonstrates outstanding optical clarity even after enduring hundreds of sandpaper abrasions,attributing to the fine metal bone structures bearing all external forces and protecting the sliding layer of SAAW.Furthermore,it exhibits exceptional resistance to biological adhesion and underwater pressure.In a green algae environment,the window remains clean with minimal change in transmittance over one month.Moreover,it retains its wettability and anti-fouling properties when subjected to a depth of 30 m of underwater pressure for 30 d.Hence,the SAAW prepared by femtosecond laser ablation and electrodeposition presents a promising strategy for developing stable optical windows in liquid environments.展开更多
基金supported by the National Natural Science Foundation of China (10772171 and 10732080)the National Basic Research Program of China (2007CB936803)
文摘Real time digital recording and numerical reconstruction of a temporal digital hologram sequence have become feasible in recent years.They provide a new measurement method which enjoys the valuable advantages of being full-field,noncontact and high precision.In this paper,a combined method of temporal digital hologram sequence and windowed Fourier transform is proposed to measure the kinematic parameters of random vibration.A series of holograms are recorded by CCD camera and the original phase can be reconstructed by Fresnel reconstruction algorithm.The three-dimensional windowed Fourier transform is used to filter noise in phase and extract the instantaneous kinematic parameters of the specimen,such as the displacement,velocity and acceleration.An experiment is conducted on a chloroprene rubber latex membrane.Results demonstrate that the proposed method determines the vibration parameters precisely and enjoys many merits.
基金Summit of the Six Top Talents Program of Jiangsu Province(No.2013-DZXX-027)Fundamental Research Funds for the Central Universities(Nos.JUSRP51510,JUSRP51323B)Graduate Student Innovation Program for Universities of Jiangsu Province(Nos.SJLX16_0500,KYLX16_0776,SJCX17_0510)
文摘In the practical measurement of signal to noise ratio(SNR)of analog-to-digital converters(ADCs)by using fast Fourier transformation(FFT)method,the non-coherent sampling is inevitable,leading to spectral leakage which in turn affects the calculation accuracy and final measurement results.In this paper,a new method based on the Blackman-Harris windowed triple-spectrum-line interpolation is presented for the measurement of ADCs SNR by FFT.The simulation platform is built based on MATLAB and the behavioral dynamic models of the high-speed ADC products of Analog Devices Inc.(ADI)are simulated.The simulation results show that,even in the case of the maximum non-coherent degree,the SNR error is less than0.23dB and reaches the testing standards provided by ADI,confirming that the proposed method is effective for suppressing the spectral leakage effects and improving the SNR test accuracy.
基金This work is supported by the National Natural Science Foundation of China(No.19801005)the Project of New Stars of Science and Technology of Beijing a Grant of Young Fellow of Educational Ministry.
文摘Let g（x） ∈L<sup>2</sup>（R） and （ω） be the Fourier transform of g（x）.Define g<sub>mn</sub>（x）=e<sup>imx</sup>g（x- 2πn）.In this paper we shall give a sufficient and necessary condition under which {g<sub>mn</sub>（x）} constitutes an orthonormal basis of L<sup>2</sup>（R） for compactly supported g（x） or （ω）.
基金Funded by the Natural Science Foundation of Guangdong(Nos.2014A030313241,2014B090901068,and 2016A010103003)。
文摘Two viologen derivatives containing fluorine substituent(F)with an asymmetric structures,1,1'-bis(4-(trifluoromethyl)phenyl)-[4,4'-bipyridine]dihexafluorophosphate(DFPV)and 1-benzyl-1'-(4-(trifluoromethyl)phenyl)-[4,4'-bipyridine]di-hexafluorophosphate(Bn-FPV),were synthesized.These viologen derivatives as active materials were used to assemble both flexible and rigid electrochromic devices(ECDs).ECDs based on DFPV exhibited reversible color change from colorless to deep green and ECDs based on Bn-FPV exhibited reversible color change from colorless to blue-green within applied voltage.It was found that the devices based on DFPV showed cycle stability,which could still maintain more than 90% after 1000 cycles.In addition,the modulation rate of the device to the solar irradiance is also calculated to characterize its application potential in smart windows.Among them,the rigid device(R-DFPV)based on the DFPV has a large solar irradiance modulation rate of 54.66%,which has the potential to be used as smart windows.
基金funded on the one hand by Agence de l'Innovation de Défense(AID)grant reference number 2021650044on the other hand by Ecole Centrale de Nantes。
文摘Joining dissimilar materials encounters significant engineering challenges due to the contrast in material properties that makes conventional welding not feasible.Magnetic Pulse Welding(MPW)offers a solidstate joining technique that overcomes these issues by using impact to create strong bonds without melting the substrate materials.This study investigates the weldability of aluminum alloy Al-5754 with Al-7075 and MARS 380 steel,used in armouring solutions of defense systems,by the use of MPW.In this work,weldability windows are investigated by varying standoff distances between the coating material and its substrate(0.25-4.5 mm)and discharge energies(5-13 kJ)with both O-shape and U-shape inductors.Mechanical strength of the welded joints were assessed through single lap shear tests,identifying optimal welding parameters.Then,the velocity profiles of the flyer plates were measured using heterodyne velocimetry to understand the dynamics of the impact.Then,substructures assembled with the optimal welding conditions were subjected to ballistic testing using 7.62 mm×51 mm NATO and 9 mm×19 mm Parabellum munitions to evaluate the resilience of the welds under ballistic impact.The outcomes demonstrate that MPW effectively joins Al-5754 with both Al-7075 and MARS 380,producing robust welds capable of withstanding ballistic impacts under certain conditions.This research advances the application of MPW in lightweight ballistic protection of defense systems,contributing to the development of more resilient and lighter protective structures.
基金National MCF Energy R&D Program(2019YFE03100400)。
文摘Ag-Cu-In-Ti low-temperature filler was used to braze the diamond and copper,and the effects of brazing temperature and soaking time on the microstructure and mechanical properties of the joints were investigated.In addition,the joint formation mechanism was discussed,and the correlation between joint microstructure and mechanical performance was established.Results show that adding appropriate amount of In into the filler can significantly reduce the filler melting point and enhance the wettability of filler on diamond.When the brazing temperature is 750°C and the soaking time is 10 min,a uniformly dense braze seam with excellent metallurgical bonding can be obtained,and its average joint shear strength reaches 322 MPa.The lower brazing temperature can mitigate the risk of diamond graphitization and also reduce the residual stresses during joining.
文摘针对现有任意反射面速度干涉仪(velocity interferometer system for any reflector,VISAR)装置中依靠人工准直光路的现状,同时为满足未来对远程自动化控制的需求,提出一种新的光路自动准直的方法。该方法通过互补金属氧化物半导体(complementary metal oxide semiconductor,CMOS)间接测量并以光斑的像素偏差为系统输入,通过系数矩阵转换和离散模糊反馈控制方法快速消除误差。基于Windows的控制和自动化技术(the Windows control and automation technology,TwinCAT)中视觉和运动等模块,将各模块分别运行在不同的实时内核中,消除了视觉与运动控制模块间的通信环节,实现了快速实时的闭环控制。经过冲击波速度测量实验验证,该系统实现了远程“一键式”自动准直,可将准直时间缩短到2 s,准直精度为4.5μm,解决了现有装置人工调节效率不高的问题,提高了系统的精度和稳定性。
基金supported by the National Key R&D Program of China(No.2022YFB3104502)the National Natural Science Foundation of China(No.62301251)+2 种基金the Natural Science Foundation of Jiangsu Province of China under Project(No.BK20220883)the open research fund of National Mobile Communications Research Laboratory,Southeast University,China(No.2024D04)the Young Elite Scientists Sponsorship Program by CAST(No.2023QNRC001).
文摘The environment of low-altitude urban airspace is complex and variable due to numerous obstacles,non-cooperative aircraft,and birds.Unmanned Aerial Vehicles(UAVs)leveraging environmental information to achieve three-dimension collision-free trajectory planning is the prerequisite to ensure airspace security.However,the timely information of surrounding situation is difficult to acquire by UAVs,which further brings security risks.As a mature technology leveraged in traditional civil aviation,the Automatic Dependent Surveillance-Broadcast(ADS-B)realizes continuous surveillance of the information of aircraft.Consequently,we leverage ADS-B for surveillance and information broadcasting,and divide the aerial airspace into multiple sub-airspaces to improve flight safety in UAV trajectory planning.In detail,we propose the secure Sub-airSpaces Planning(SSP)algorithm and Particle Swarm Optimization Rapidly-exploring Random Trees(PSO-RRT)algorithm for the UAV trajectory planning in law-altitude airspace.The performance of the proposed algorithm is verified by simulations and the results show that SSP reduces both the maximum number of UAVs in the sub-airspace and the length of the trajectory,and PSO-RRT reduces the cost of UAV trajectory in the sub-airspace.
基金supported by the National Science Foundation of China under Grant Nos(Nos.12127806,62175195)the International Joint Research Laboratory for Micro/Nano Manufacturing and Measurement Technologies。
文摘Transparent materials utilized as underwater optical windows are highly vulnerable to various forms of pollution or abrasion due to their intrinsic hydrophilic properties.This susceptibility is particularly pronounced in underwater environments where pollutants can impede the operation of these optical devices,significantly degrading or even compromising their optical properties.The glass catfish,known for its remarkable transparency in water,maintains surface cleanliness and clarity despite exposure to contaminants,impurities abrasion,and hydraulic pressure.Inspired by the glass catfish’s natural attributes,this study introduces a new solution named subaquatic abrasion-resistant and anti-fouling window(SAAW).Utilizing femtosecond laser ablation and electrodeposition,the SAAW is engineered by embedding fine metal bone structures into a transparent substrate and anti-fouling sliding layer,akin to the sturdy bones among catfish’s body.This approach significantly bolsters the window’s abrasion resistance and anti-fouling performance while maintaining high light transmittance.The sliding layer on the SAAW’s surface remarkably reduces the friction of various liquids,which is the reason that SAAW owns the great anti-fouling property.The SAAW demonstrates outstanding optical clarity even after enduring hundreds of sandpaper abrasions,attributing to the fine metal bone structures bearing all external forces and protecting the sliding layer of SAAW.Furthermore,it exhibits exceptional resistance to biological adhesion and underwater pressure.In a green algae environment,the window remains clean with minimal change in transmittance over one month.Moreover,it retains its wettability and anti-fouling properties when subjected to a depth of 30 m of underwater pressure for 30 d.Hence,the SAAW prepared by femtosecond laser ablation and electrodeposition presents a promising strategy for developing stable optical windows in liquid environments.
