The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes （LEDs） is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelen...The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes （LEDs） is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelengths and larger wavelengths with the increasing current, which results from the Mg-dopant-related polarization screening. The LEDs show enhanced efficiency with the decreasing Mg back-diffusion in the lower current region. Light outputs follow the power law L α I^m, with smaller parameter m in the LEDs with less Mg back-diffusion, indicating a lower density of trap states. The trap-assisted tunneling current is also suppressed by reducing Mg- defect-related nonradiative centers in the active region. Furthermore, the forward current-voltage characteristics are improved.展开更多
This paper introduces an innovative approach to the synchronized demand-capacity balance with special focus on sector capacity uncertainty within a centrally controlled collaborative air traffic flow management(ATFM)f...This paper introduces an innovative approach to the synchronized demand-capacity balance with special focus on sector capacity uncertainty within a centrally controlled collaborative air traffic flow management(ATFM)framework.Further with previous study,the uncertainty in capacity is considered as a non-negligible issue regarding multiple reasons,like the impact of weather,the strike of air traffic controllers(ATCOs),the military use of airspace and the spatiotemporal distribution of nonscheduled flights,etc.These recessive factors affect the outcome of traffic flow optimization.In this research,the focus is placed on the impact of sector capacity uncertainty on demand and capacity balancing(DCB)optimization and ATFM,and multiple options,such as delay assignment and rerouting,are intended for regulating the traffic flow.A scenario optimization method for sector capacity in the presence of uncertainties is used to find the approximately optimal solution.The results show that the proposed approach can achieve better demand and capacity balancing and determine perfect integer solutions to ATFM problems,solving large-scale instances(24 h on seven capacity scenarios,with 6255 flights and 8949 trajectories)in 5-15 min.To the best of our knowledge,our experiment is the first to tackle large-scale instances of stochastic ATFM problems within the collaborative ATFM framework.展开更多
Based on the anti-jamming performance of differential frequency hopping （DFH） systems in Additive White Gaussian Noise （AWGN） channel, Fountain code is introduced to the DFH systems as the outer error correcting c...Based on the anti-jamming performance of differential frequency hopping （DFH） systems in Additive White Gaussian Noise （AWGN） channel, Fountain code is introduced to the DFH systems as the outer error correcting code in this paper to investigate the improvements against partial-band jamming over AWGN channel. The performance of Fountain coded DFH is theoretically analyzed and numerically simulated. The total frequency of hopping in the simulation is 16, and results show that, on one hand, when exact jamming state information （JSI） is available, and the number of jamming frequency is n= 16, the bit error rate （BER） of 10~3 is achieved with the signal to interference ratio （SIR） approximately 7.5 dB over AWGN channel, and the performance improves about 1-1.5dB compared with the no-coded system. When the number of jamming frequency is n=2, the performance increases 15-17dB. On the other hand, when JSI is unavailable, a joint JSI estimation and decoding algorithm is proposed. The BER of 10 3 is achieved with jamming-frequency n 16, SIR=8dB and signal noise ratio （SNR） 10dB over AWGN channel. It＇s proved that this algorithm provides robust anti-jamming pertbrmance even without JSI. The anti-jamming performance of Fountain coded DFH systems is obviously superior to no-coded DFH systems.展开更多
The energy conversion efficiency of a multistage synchronous induction coilgun(MSSICG) has become one of the key factors that restricts its industrialization. To improve the launch efficiency of medium-and high-veloci...The energy conversion efficiency of a multistage synchronous induction coilgun(MSSICG) has become one of the key factors that restricts its industrialization. To improve the launch efficiency of medium-and high-velocity MSSICG,we propose an optimization design scheme combining orthogonal experimental design(OED) and self-consistent design method in this paper. The OED is introduced to reduce the number of iterations and improve the identification accuracy and efficiency. A self-consistent design model is established to overcome a defect that the parameters that need to be optimized will multiply as the number of coil stages increases. The influence of six factors(radial thickness of armature, axial length of armature, axial length of coil, capacitance, wire diameter, and slip speed) on the launch efficiency are then evaluated by range analysis. This work presents a valuable reference for optimizing medium-and high-velocity MSSICG.展开更多
Metasurface-based nanoprinting(meta-nanoprinting)has fully demonstrated its advantages in ultrahigh-density gray-scale/color image recording and display.A typical meta-nanoprinting device usually has image resolutions...Metasurface-based nanoprinting(meta-nanoprinting)has fully demonstrated its advantages in ultrahigh-density gray-scale/color image recording and display.A typical meta-nanoprinting device usually has image resolutions reaching 80 k dots per inch(dpi),far exceeding conventional technology such as gravure printing(typ.5 k dpi).Besides,by fully exploit-ing the design degrees of freedom of nanostructured metasurfaces,meta-nanoprinting has been developed from previ-ous single-channel to multiple-channels,to current multifunctional integration or even dynamic display.In this review,we overview the development of meta-nanoprinting,including the physics of nanoprinting to manipulate optical amplitude and spectrum,single-functional meta-nanoprinting,multichannel meta-nanoprinting,dynamic meta-nanoprinting and mul-tifunctional metasurface integrating nanoprinting with holography or metalens,etc.Applications of meta-nanoprinting such as image display,vortex beam generation,information decoding and hiding,information encryption,high-density optical storage and optical anti-counterfeiting have also been discussed.Finally,we conclude the opportunities and chal-lenges/perspectives in this rapidly developing research field of meta-nanoprinting.展开更多
We design a new chaotic oscillator based on the realistic model of the HP TiO_(2) memristor and Chua's circuit.Some basic dynamical behaviors of the oscillator,including equilibrium set,Lyapunov exponent spectrum ...We design a new chaotic oscillator based on the realistic model of the HP TiO_(2) memristor and Chua's circuit.Some basic dynamical behaviors of the oscillator,including equilibrium set,Lyapunov exponent spectrum and bifurcations with respect to various circuit parameters,are investigated theoretically and numerically.Chaotic attractors generated by the proposed oscillator are described with simulations and experiments,showing a good agreement.The main finding by analysis is that the proposed oscillator has no transient chaos and weak hyperchaos appears.Furthermore,its stability is insensitive to its initial values,thereby generating continuous and stable chaotic oscillation signals for chaos-based applications.展开更多
From the sound velocity measured using the Brillouin scattering technique, the elastic, piezoelectric, and dielectric constants of a high-quality monodomain tetragonal Rh：BaTiO3 single crystal are determined at room ...From the sound velocity measured using the Brillouin scattering technique, the elastic, piezoelectric, and dielectric constants of a high-quality monodomain tetragonal Rh：BaTiO3 single crystal are determined at room temperature. The elastic constants are in fairly good agreement with those of the BaTiO3 single crystal, measured previously by Brillouin scattering and the low-frequency equivalent circuit methods. However, their electromeehanical properties are significantly different. Based on the sound propagation equations and these results, the directional dependence of the compressional modulus and the shear modulus of Rh：BaTiO3 in the （010） plane is investigated. Some properties of sound propagation and electromechanical coupling in the crystal are discussed.展开更多
Contactless manipulation of multi-scale objects using the acoustic vortex(AV) tweezers offers tremendous perspectives in biomedical applications.However,it is still hindered by the weak acoustic radiation force(ARF) a...Contactless manipulation of multi-scale objects using the acoustic vortex(AV) tweezers offers tremendous perspectives in biomedical applications.However,it is still hindered by the weak acoustic radiation force(ARF) and torque(ART)around the vortex center.By introducing the elevation angle to the planar transducers of an N-element ring array,the weakfocused acoustic vortex(WFAV) composed of a main-AV and N paraxial-AVs is constructed to conduct a large-scale object manipulation.Different from the traditional focused AV(FAV) generated by a ring array of concave spherical transducers,a much larger focal region of the WFAV is generated by the main lobes of the planar transducers with the size inversely associated with the elevation angle.With the pressure simulation of the acoustic field,the capability of the rotational object driving in the focal plane for the WFAV is analyzed using the ARF and the ART exerted on an elastic ball based on acoustic scattering.With the experimental system built in water,the generation of the WFAV is verified by the scanning measurements of the acoustic field and the capability of object manipulation is also analyzed by the rotational trapping of floating particles in the focal plane.The favorable results demonstrate the feasibility of large-scale rotational manipulation of objects with a strengthened ART and a reduced acousto-thermal damage to biological tissues,showing a promising prospect for potential applications in clinical practice.展开更多
GNSS-R technology has been gradually applied to marine remote sensing,land detection,wind speed measurement,etc. due to its advantages of passive,all-weather,and frequent revisiting period. Thus,research on the spaceb...GNSS-R technology has been gradually applied to marine remote sensing,land detection,wind speed measurement,etc. due to its advantages of passive,all-weather,and frequent revisiting period. Thus,research on the spaceborne GNSS-R technology has received increasing attention. This paper,based on the spaceborne GNSS-R data,verified the feasibility and effectiveness of using neural networks based on the delay Doppler map(DDM) data to retrieve wind speeds,estimate soil moisture,and map the position of the sea ice by using DDM spectra.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 61505197 and 61334009the National High-Technology Research and Development Program of China under Grant No 2014AA032604
文摘The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes （LEDs） is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelengths and larger wavelengths with the increasing current, which results from the Mg-dopant-related polarization screening. The LEDs show enhanced efficiency with the decreasing Mg back-diffusion in the lower current region. Light outputs follow the power law L α I^m, with smaller parameter m in the LEDs with less Mg back-diffusion, indicating a lower density of trap states. The trap-assisted tunneling current is also suppressed by reducing Mg- defect-related nonradiative centers in the active region. Furthermore, the forward current-voltage characteristics are improved.
文摘This paper introduces an innovative approach to the synchronized demand-capacity balance with special focus on sector capacity uncertainty within a centrally controlled collaborative air traffic flow management(ATFM)framework.Further with previous study,the uncertainty in capacity is considered as a non-negligible issue regarding multiple reasons,like the impact of weather,the strike of air traffic controllers(ATCOs),the military use of airspace and the spatiotemporal distribution of nonscheduled flights,etc.These recessive factors affect the outcome of traffic flow optimization.In this research,the focus is placed on the impact of sector capacity uncertainty on demand and capacity balancing(DCB)optimization and ATFM,and multiple options,such as delay assignment and rerouting,are intended for regulating the traffic flow.A scenario optimization method for sector capacity in the presence of uncertainties is used to find the approximately optimal solution.The results show that the proposed approach can achieve better demand and capacity balancing and determine perfect integer solutions to ATFM problems,solving large-scale instances(24 h on seven capacity scenarios,with 6255 flights and 8949 trajectories)in 5-15 min.To the best of our knowledge,our experiment is the first to tackle large-scale instances of stochastic ATFM problems within the collaborative ATFM framework.
基金the National Natural Science Foundation of China under Grant 61371125
文摘Based on the anti-jamming performance of differential frequency hopping （DFH） systems in Additive White Gaussian Noise （AWGN） channel, Fountain code is introduced to the DFH systems as the outer error correcting code in this paper to investigate the improvements against partial-band jamming over AWGN channel. The performance of Fountain coded DFH is theoretically analyzed and numerically simulated. The total frequency of hopping in the simulation is 16, and results show that, on one hand, when exact jamming state information （JSI） is available, and the number of jamming frequency is n= 16, the bit error rate （BER） of 10~3 is achieved with the signal to interference ratio （SIR） approximately 7.5 dB over AWGN channel, and the performance improves about 1-1.5dB compared with the no-coded system. When the number of jamming frequency is n=2, the performance increases 15-17dB. On the other hand, when JSI is unavailable, a joint JSI estimation and decoding algorithm is proposed. The BER of 10 3 is achieved with jamming-frequency n 16, SIR=8dB and signal noise ratio （SNR） 10dB over AWGN channel. It＇s proved that this algorithm provides robust anti-jamming pertbrmance even without JSI. The anti-jamming performance of Fountain coded DFH systems is obviously superior to no-coded DFH systems.
基金Project supported by the National Natural Science Foundation of China(Grant No.5140130)
文摘The energy conversion efficiency of a multistage synchronous induction coilgun(MSSICG) has become one of the key factors that restricts its industrialization. To improve the launch efficiency of medium-and high-velocity MSSICG,we propose an optimization design scheme combining orthogonal experimental design(OED) and self-consistent design method in this paper. The OED is introduced to reduce the number of iterations and improve the identification accuracy and efficiency. A self-consistent design model is established to overcome a defect that the parameters that need to be optimized will multiply as the number of coil stages increases. The influence of six factors(radial thickness of armature, axial length of armature, axial length of coil, capacitance, wire diameter, and slip speed) on the launch efficiency are then evaluated by range analysis. This work presents a valuable reference for optimizing medium-and high-velocity MSSICG.
基金We are grateful for financial supports from the National Key Research and Development Program of China(Grant No.2021YFE0205800)National Natural Science Foundation of China(Grant Nos.12174292,62205252,11904267 and 91950110)the Fundamental Research Funds for the Central Universities(Grant Nos.2042022kf0024,2042022kf1013 and 2042022kf1011).
文摘Metasurface-based nanoprinting(meta-nanoprinting)has fully demonstrated its advantages in ultrahigh-density gray-scale/color image recording and display.A typical meta-nanoprinting device usually has image resolutions reaching 80 k dots per inch(dpi),far exceeding conventional technology such as gravure printing(typ.5 k dpi).Besides,by fully exploit-ing the design degrees of freedom of nanostructured metasurfaces,meta-nanoprinting has been developed from previ-ous single-channel to multiple-channels,to current multifunctional integration or even dynamic display.In this review,we overview the development of meta-nanoprinting,including the physics of nanoprinting to manipulate optical amplitude and spectrum,single-functional meta-nanoprinting,multichannel meta-nanoprinting,dynamic meta-nanoprinting and mul-tifunctional metasurface integrating nanoprinting with holography or metalens,etc.Applications of meta-nanoprinting such as image display,vortex beam generation,information decoding and hiding,information encryption,high-density optical storage and optical anti-counterfeiting have also been discussed.Finally,we conclude the opportunities and chal-lenges/perspectives in this rapidly developing research field of meta-nanoprinting.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61271064 and 60971046the Natural Science Foundation of Zhejiang Province under Grant No LZ12F01001.
文摘We design a new chaotic oscillator based on the realistic model of the HP TiO_(2) memristor and Chua's circuit.Some basic dynamical behaviors of the oscillator,including equilibrium set,Lyapunov exponent spectrum and bifurcations with respect to various circuit parameters,are investigated theoretically and numerically.Chaotic attractors generated by the proposed oscillator are described with simulations and experiments,showing a good agreement.The main finding by analysis is that the proposed oscillator has no transient chaos and weak hyperchaos appears.Furthermore,its stability is insensitive to its initial values,thereby generating continuous and stable chaotic oscillation signals for chaos-based applications.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10874236 and 60808010)
文摘From the sound velocity measured using the Brillouin scattering technique, the elastic, piezoelectric, and dielectric constants of a high-quality monodomain tetragonal Rh：BaTiO3 single crystal are determined at room temperature. The elastic constants are in fairly good agreement with those of the BaTiO3 single crystal, measured previously by Brillouin scattering and the low-frequency equivalent circuit methods. However, their electromeehanical properties are significantly different. Based on the sound propagation equations and these results, the directional dependence of the compressional modulus and the shear modulus of Rh：BaTiO3 in the （010） plane is investigated. Some properties of sound propagation and electromechanical coupling in the crystal are discussed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11934009,11974187,and 12004187)the Natural Science Foundation of Jiangsu Province,China(Grant Nos.BK20161013 and BK20200724)。
文摘Contactless manipulation of multi-scale objects using the acoustic vortex(AV) tweezers offers tremendous perspectives in biomedical applications.However,it is still hindered by the weak acoustic radiation force(ARF) and torque(ART)around the vortex center.By introducing the elevation angle to the planar transducers of an N-element ring array,the weakfocused acoustic vortex(WFAV) composed of a main-AV and N paraxial-AVs is constructed to conduct a large-scale object manipulation.Different from the traditional focused AV(FAV) generated by a ring array of concave spherical transducers,a much larger focal region of the WFAV is generated by the main lobes of the planar transducers with the size inversely associated with the elevation angle.With the pressure simulation of the acoustic field,the capability of the rotational object driving in the focal plane for the WFAV is analyzed using the ARF and the ART exerted on an elastic ball based on acoustic scattering.With the experimental system built in water,the generation of the WFAV is verified by the scanning measurements of the acoustic field and the capability of object manipulation is also analyzed by the rotational trapping of floating particles in the focal plane.The favorable results demonstrate the feasibility of large-scale rotational manipulation of objects with a strengthened ART and a reduced acousto-thermal damage to biological tissues,showing a promising prospect for potential applications in clinical practice.
文摘GNSS-R technology has been gradually applied to marine remote sensing,land detection,wind speed measurement,etc. due to its advantages of passive,all-weather,and frequent revisiting period. Thus,research on the spaceborne GNSS-R technology has received increasing attention. This paper,based on the spaceborne GNSS-R data,verified the feasibility and effectiveness of using neural networks based on the delay Doppler map(DDM) data to retrieve wind speeds,estimate soil moisture,and map the position of the sea ice by using DDM spectra.
