The Ultrasonic Electric Propulsion(UEP)system is a cutting-edge propulsion technology that is mostly used on platforms for small satellites(less than 10 kg).The characteristics of droplet partial emissions(DPEs)in the...The Ultrasonic Electric Propulsion(UEP)system is a cutting-edge propulsion technology that is mostly used on platforms for small satellites(less than 10 kg).The characteristics of droplet partial emissions(DPEs)in the UEP system are investigated using a high-speed imaging technique(an ultra-high speed camera(NAC HX-6)and a long-distance microscope)in this work.The experiments demonstrate that there are a few partial emission modes,including left-side emission,double-side emission,and right-side emission,that are present in the droplet emission process of the UEP system.These modes are primarily caused by the partial formation of capillary standing waves(CSWs)on the emission surface of the ultrasonic nozzle.The emission rate for single-and double-sided emissions varies at different times,indicating that there are different CSWs engaged in droplet emission due to variations in the liquid film thickness and charge state of the liquid cones.Additionally,as the droplets emit continuously,a raised area on the emission surface appears,with several droplets emitting there as a result of charge accumulation.Additionally,photos of the CSWs with emitting droplets are obtained,which highlights the CSWs'distinctive wave morphology.展开更多
In this study,a pulsed,high voltage driven hollow-cathode electron beam sources through an optical trigger is designed with characteristics of simple structure,low cost,and easy triggering.To validate the new design,t...In this study,a pulsed,high voltage driven hollow-cathode electron beam sources through an optical trigger is designed with characteristics of simple structure,low cost,and easy triggering.To validate the new design,the characteristics of hollow-cathode discharge and electron beam characterization under pulsed high voltage drive are studied experimentally and discussed by discharge characteristics and analyses of waveform details,respectively.The validation experiments indicate that the pulsed high voltage supply significantly improves the frequency and stability of the discharge,which provides a new solution for the realization of a high-frequency,high-energy electron beam source.The peak current amplitude in the high-energy electron beam increases from 6.2 A to 79.6 A,which indicates the pulsed power mode significantly improves the electron beam performance.Besides,increasing the capacitance significantly affects the highcurrent,lower-energy electron beam more than the high-energy electron beam.展开更多
Lithium-sulfur(Li-S)batteries are receiving increasing attention as one of the potential next-generation batteries,owing to their high energy densities and low cost.However,practical Li-S batteries with high energy de...Lithium-sulfur(Li-S)batteries are receiving increasing attention as one of the potential next-generation batteries,owing to their high energy densities and low cost.However,practical Li-S batteries with high energy densities are extremely hindered by the sulfur loss,low Coulombic efficiency,and short cycling life originating from the polysulfide(LiPS)shuttle.In this study,two-dimensional(2D)ZnCo_(2)O_(4) microsheets fabricated by a facile hydrothermal process are employed to modify the separator,for improving the electrochemical performances of Li-S cells.The resulting 2D Zn Co_(2)O_(4)-coated separator features a coating thickness of approximately 10 lm,high ionic conductivity of 1.8 m S/cm,and low mass loading of 0.2 mg/cm^(2).This 2D ZnCo_(2)O_(4)-coated separator effectively inhibits Li PS shuttle by a strong chemical interaction with Li PS as well as promotes the redox kinetics by Zn CO2O4-coated layers,as determined by X-ray photoelectron spectroscopy analysis,self-discharge,time-dependent permeation test,Li symmetric cell test,and Li2S nucleation analyses.Consequently,the Li-S batteries based on the 2D Zn Co_(2)O_(4)-coated separator exhibit a high initial discharge capacity of 1292.2 m Ah/g at 0.1 C.Moreover,they exhibit excellent long cycle stability at 1 and 2 C with capacity retention of 84%and 86%even after800 cycles,corresponding to a capacity fading rate of 0.020%and 0.016%per cycle,respectively.Effectively,these Li-S cells with a high sulfur loading at 5.3 mg/cm^(2) and low electrolyte concentration of 9 l L/mg deliver a high discharge capacity of 4.99 m Ah/cm^(2) after 200 cycles at 0.1 C.展开更多
A three-dimensional model of the double-slot coupled cavity slow-wave structure （CCSWS） with a solid round elec- tron beam for the beam-wave interaction is presented. Based on the ＂cold＂ dispersion, the ＂hot＂ di...A three-dimensional model of the double-slot coupled cavity slow-wave structure （CCSWS） with a solid round elec- tron beam for the beam-wave interaction is presented. Based on the ＂cold＂ dispersion, the ＂hot＂ dispersion equation is derived with the Maxwell equations by using the variable separation method and the field-matching method. Through numerical calculations, the effects of the electron beam parameters and the staggered angle between adjacent walls on the linear gain are analyzed.展开更多
The main geolocation technology currently used in COSPAS-SARSAT system is TDOA/FDOA or three-star TDOA,the principle is to determine the location of the signal source by using the difference in arrival time and freque...The main geolocation technology currently used in COSPAS-SARSAT system is TDOA/FDOA or three-star TDOA,the principle is to determine the location of the signal source by using the difference in arrival time and frequency of the wireless signal between different receivers.Therefore,ground monitoring stations need to be equipped with more than two antenna receiving stations,and multiple satellites should be able to simultaneously relay the distress signal from the target source in order to achieve the geolocation function.However,when the ground receiving system has only one antenna receiving station,or the target source is in a heavily obscured environment,the ground side is unable to receive the forwarded signals from multiple satellites at the same time,which will make it impossible to locate.To address these problems,in this paper,a time-sharing single satellite geolocations method based on different orbits is proposed for the first time.This method uses one or several low-earth orbit satellites(LEO)and mediumearth orbit satellites(MEO)in the visible area,and the receiving station only needs one pair of receiving antennas to complete the positioning.It can effectively compensate for the shortcomings of the traditional TDOA using the same moment and have better positioning accuracy compared with the single satellite in the same orbit.Due to the limited experimental conditions,this paper tests the navigation satellite using different orbit time-sharing single satellite geolocations,and proves that the positioning method has high positioning accuracy and has certain promotion and application value.展开更多
This paper presented a joint resource allocation(RA) and admission control(AC) mechanism in software defined mobile networks(SDMNs). In this mechanism, the joint RA and AC problem can be formulated as an optimization ...This paper presented a joint resource allocation(RA) and admission control(AC) mechanism in software defined mobile networks(SDMNs). In this mechanism, the joint RA and AC problem can be formulated as an optimization problem with the aim of maximizing the number of admitted users while simultaneously minimizing the number of allocated channels. Since the primal problem is modeled to be a mixed integer nonlinear problem(MINLP), we attain the suboptimal solutions to the primal MINLP by convex relaxation. Additionally, with the global information collected by the SDMNs controller, a centralized joint RA and AC(CJRA)algorithm is proposed by the Lagrange dual decomposition technique to obtain the global optimum. Meanwhile, we propose an OpenFlow rules placement strategy to realize CJRA in an efficient way. Moreover, a distributed algorithm is also developed to find the local optimum, showing a performance benchmark for the centralized one. Finally, simulation results show that the proposed centralized algorithm admits more users compared with the distributed.展开更多
The output intensity variations of the laser used in a prism coupling system are observed and found to be induced by the external optical feedback, which comes from the reflection on the prism. The intensity variation...The output intensity variations of the laser used in a prism coupling system are observed and found to be induced by the external optical feedback, which comes from the reflection on the prism. The intensity variations are explained with laser theory. The trough in the intensity variation corresponds to the position of the prism when the output light beam propagates perpendicularly to the prism. Based on the trough a new method for rotating the prism and reading out the step numbers is proposed, by which the angle 0° in the system need not to be calibrated. It is proven by experiment that the new method would improve the accuracy of the refractive index up to ±0.00001 and thickness to ±1 nm.展开更多
Quantum key distribution is the art of sharing secret keys between two distant parties, and has attracted a lot of attention due to its unconditional security. Compared with other quantum key distribution protocols, t...Quantum key distribution is the art of sharing secret keys between two distant parties, and has attracted a lot of attention due to its unconditional security. Compared with other quantum key distribution protocols, the differential phase shift quantum key distribution protocol has higher efficiency and simpler apparatus. Unfortunately, the uncondi- tional security of differential phase shift quantum key distribution has not been proved. Utilizing the sharp continuity of the von Neuman entropy and some basic inequalities, we estimate the upper bound for the eavesdropper Eve＇s infor- mation. We then prove the lower bound for the security of the differential phase shift quantum key distribution protocol against a one-pulse attack with Devatak-Winter＇s secret key rate formula.展开更多
This paper considers a two-phase free boundary problem for coupled system including one parabolic equation and two elliptic equations. The problem comes from the discussion of a growth model of self-maintaining protoc...This paper considers a two-phase free boundary problem for coupled system including one parabolic equation and two elliptic equations. The problem comes from the discussion of a growth model of self-maintaining protocell in multidimensional case. The local classical solution of the problem with free boundary (?) y = g(x,t) between two domains is being seeked. The local existence and uniqueness of the problem will be proved in multidimensional case.展开更多
The degradation mechanism of GaN-based near-ultraviolet(NUV,320-400 nm)light emitting diodes(LEDs)with low-indium content under electrical stress is studied from the aspect of defects.A decrease in the optical power a...The degradation mechanism of GaN-based near-ultraviolet(NUV,320-400 nm)light emitting diodes(LEDs)with low-indium content under electrical stress is studied from the aspect of defects.A decrease in the optical power and an increase in the leakage current are observed after electrical stress.The defect behaviors are characterized using deep level transient spectroscopy(DLTS)measurement under different filling pulse widths.After stress,the concentration of defects with the energy level of 0.47-0.56 eV increases,accompanied by decrease in the concentration of 0.72-0.84 eV defects.Combing the defect energy level with the increased yellow luminescence in photoluminescence spectra,the device degradation can be attributed to the activation of the gallium vacancy and oxygen related complex defect along dislocation,which was previously passivated with hydrogen.This study reveals the evolution process of defects under electrical stress and their spatial location,laying a foundation for manufacture of GaN-based NUV LEDs with high reliability.展开更多
In a recent paper, Sacchi （Phys. Rev. Lett. 96 （2006） 220502） studied the information-disturbance tradeoff in estimating an unknown two-qubit maximally entangled state. In this study, we explore the tradeoff in es...In a recent paper, Sacchi （Phys. Rev. Lett. 96 （2006） 220502） studied the information-disturbance tradeoff in estimating an unknown two-qubit maximally entangled state. In this study, we explore the tradeoff in estimating 13 an unknown three-qubit GHZ state. The optimal estimation process supplies a fidelity of 13/54 and the tradeoff interpolates smoothly between non-informative measurement and optimal estimation process.展开更多
Combining the mutual information theory and the sequential hypothesis testing(SHT)method,a selfadapting radio frequency(RF)stealth signal design method is proposed. The channel information is gained through the radar ...Combining the mutual information theory and the sequential hypothesis testing(SHT)method,a selfadapting radio frequency(RF)stealth signal design method is proposed. The channel information is gained through the radar echo and feeds back to the radar system,and then the radar system adaptively designs the transmission waveform. So the close-loop system is formed. The correlations between these transmission waveforms are decreased because of the adaptive change of these transmission waveforms,and the number of illuminations is reduced for adopting the SHT,which lowers the transmission power of the radar system. The radar system using the new method possesses the RF stealth performance. Aiming at the application of radar automatic target recognition(RATR),experimental simulations show the effectiveness and feasibility of the proposed method.展开更多
基金supported by National Natural Science Foundation of China(No.12102099)the National Key R&D Program of China(No.2021YFC2202700)the Outstanding Academic Leader Project of Shanghai(Youth)(No.23XD1421700),respectively。
文摘The Ultrasonic Electric Propulsion(UEP)system is a cutting-edge propulsion technology that is mostly used on platforms for small satellites(less than 10 kg).The characteristics of droplet partial emissions(DPEs)in the UEP system are investigated using a high-speed imaging technique(an ultra-high speed camera(NAC HX-6)and a long-distance microscope)in this work.The experiments demonstrate that there are a few partial emission modes,including left-side emission,double-side emission,and right-side emission,that are present in the droplet emission process of the UEP system.These modes are primarily caused by the partial formation of capillary standing waves(CSWs)on the emission surface of the ultrasonic nozzle.The emission rate for single-and double-sided emissions varies at different times,indicating that there are different CSWs engaged in droplet emission due to variations in the liquid film thickness and charge state of the liquid cones.Additionally,as the droplets emit continuously,a raised area on the emission surface appears,with several droplets emitting there as a result of charge accumulation.Additionally,photos of the CSWs with emitting droplets are obtained,which highlights the CSWs'distinctive wave morphology.
基金supported by National Natural Science Foundation of China(No.12102099)the National Key R&D Program of China(No.2021YFC2202700)the Outstanding Academic Leader Project of Shanghai(Youth)(No.23XD1421700),respectively。
文摘In this study,a pulsed,high voltage driven hollow-cathode electron beam sources through an optical trigger is designed with characteristics of simple structure,low cost,and easy triggering.To validate the new design,the characteristics of hollow-cathode discharge and electron beam characterization under pulsed high voltage drive are studied experimentally and discussed by discharge characteristics and analyses of waveform details,respectively.The validation experiments indicate that the pulsed high voltage supply significantly improves the frequency and stability of the discharge,which provides a new solution for the realization of a high-frequency,high-energy electron beam source.The peak current amplitude in the high-energy electron beam increases from 6.2 A to 79.6 A,which indicates the pulsed power mode significantly improves the electron beam performance.Besides,increasing the capacitance significantly affects the highcurrent,lower-energy electron beam more than the high-energy electron beam.
基金supported by a grant from R&D Program of the Korea Railroad Research Institute,Republic of Korea。
文摘Lithium-sulfur(Li-S)batteries are receiving increasing attention as one of the potential next-generation batteries,owing to their high energy densities and low cost.However,practical Li-S batteries with high energy densities are extremely hindered by the sulfur loss,low Coulombic efficiency,and short cycling life originating from the polysulfide(LiPS)shuttle.In this study,two-dimensional(2D)ZnCo_(2)O_(4) microsheets fabricated by a facile hydrothermal process are employed to modify the separator,for improving the electrochemical performances of Li-S cells.The resulting 2D Zn Co_(2)O_(4)-coated separator features a coating thickness of approximately 10 lm,high ionic conductivity of 1.8 m S/cm,and low mass loading of 0.2 mg/cm^(2).This 2D ZnCo_(2)O_(4)-coated separator effectively inhibits Li PS shuttle by a strong chemical interaction with Li PS as well as promotes the redox kinetics by Zn CO2O4-coated layers,as determined by X-ray photoelectron spectroscopy analysis,self-discharge,time-dependent permeation test,Li symmetric cell test,and Li2S nucleation analyses.Consequently,the Li-S batteries based on the 2D Zn Co_(2)O_(4)-coated separator exhibit a high initial discharge capacity of 1292.2 m Ah/g at 0.1 C.Moreover,they exhibit excellent long cycle stability at 1 and 2 C with capacity retention of 84%and 86%even after800 cycles,corresponding to a capacity fading rate of 0.020%and 0.016%per cycle,respectively.Effectively,these Li-S cells with a high sulfur loading at 5.3 mg/cm^(2) and low electrolyte concentration of 9 l L/mg deliver a high discharge capacity of 4.99 m Ah/cm^(2) after 200 cycles at 0.1 C.
基金Project supported by the National Natural Science Foundation of China(Grant No.11205162)
文摘A three-dimensional model of the double-slot coupled cavity slow-wave structure （CCSWS） with a solid round elec- tron beam for the beam-wave interaction is presented. Based on the ＂cold＂ dispersion, the ＂hot＂ dispersion equation is derived with the Maxwell equations by using the variable separation method and the field-matching method. Through numerical calculations, the effects of the electron beam parameters and the staggered angle between adjacent walls on the linear gain are analyzed.
基金supported by National Science Foundation of China(No.91738201,U21A20450)。
文摘The main geolocation technology currently used in COSPAS-SARSAT system is TDOA/FDOA or three-star TDOA,the principle is to determine the location of the signal source by using the difference in arrival time and frequency of the wireless signal between different receivers.Therefore,ground monitoring stations need to be equipped with more than two antenna receiving stations,and multiple satellites should be able to simultaneously relay the distress signal from the target source in order to achieve the geolocation function.However,when the ground receiving system has only one antenna receiving station,or the target source is in a heavily obscured environment,the ground side is unable to receive the forwarded signals from multiple satellites at the same time,which will make it impossible to locate.To address these problems,in this paper,a time-sharing single satellite geolocations method based on different orbits is proposed for the first time.This method uses one or several low-earth orbit satellites(LEO)and mediumearth orbit satellites(MEO)in the visible area,and the receiving station only needs one pair of receiving antennas to complete the positioning.It can effectively compensate for the shortcomings of the traditional TDOA using the same moment and have better positioning accuracy compared with the single satellite in the same orbit.Due to the limited experimental conditions,this paper tests the navigation satellite using different orbit time-sharing single satellite geolocations,and proves that the positioning method has high positioning accuracy and has certain promotion and application value.
基金supported by the National Natural Science Foundation of China under Grant No.61701284,61472229,31671588 and 61801270the China Postdoctoral Science Foundation Funded Project under Grant No2017M622233+2 种基金the Application Research Project for Postdoctoral Researchers of Qingdao,the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents under Grant No.2016RCJJ010the Sci.&Tech.DevelopmentFund of Shandong Province of China underGrant No.2016ZDJS02A11,ZR2017BF015and ZR2017MF027the Taishan Scholar Climbing Program of Shandong Province,and SDUST Research Fund under Grant No.2015TDJH102
文摘This paper presented a joint resource allocation(RA) and admission control(AC) mechanism in software defined mobile networks(SDMNs). In this mechanism, the joint RA and AC problem can be formulated as an optimization problem with the aim of maximizing the number of admitted users while simultaneously minimizing the number of allocated channels. Since the primal problem is modeled to be a mixed integer nonlinear problem(MINLP), we attain the suboptimal solutions to the primal MINLP by convex relaxation. Additionally, with the global information collected by the SDMNs controller, a centralized joint RA and AC(CJRA)algorithm is proposed by the Lagrange dual decomposition technique to obtain the global optimum. Meanwhile, we propose an OpenFlow rules placement strategy to realize CJRA in an efficient way. Moreover, a distributed algorithm is also developed to find the local optimum, showing a performance benchmark for the centralized one. Finally, simulation results show that the proposed centralized algorithm admits more users compared with the distributed.
文摘The output intensity variations of the laser used in a prism coupling system are observed and found to be induced by the external optical feedback, which comes from the reflection on the prism. The intensity variations are explained with laser theory. The trough in the intensity variation corresponds to the position of the prism when the output light beam propagates perpendicularly to the prism. Based on the trough a new method for rotating the prism and reading out the step numbers is proposed, by which the angle 0° in the system need not to be calibrated. It is proven by experiment that the new method would improve the accuracy of the refractive index up to ±0.00001 and thickness to ±1 nm.
基金supported by the National Fundamental Research Program of China (Grant No. 2006CB921900)National Natural Science Foundation of China (Grant Nos. 60537020 and 60621064)the Innovation Funds of the Chinese Academy of Sciences
文摘Quantum key distribution is the art of sharing secret keys between two distant parties, and has attracted a lot of attention due to its unconditional security. Compared with other quantum key distribution protocols, the differential phase shift quantum key distribution protocol has higher efficiency and simpler apparatus. Unfortunately, the uncondi- tional security of differential phase shift quantum key distribution has not been proved. Utilizing the sharp continuity of the von Neuman entropy and some basic inequalities, we estimate the upper bound for the eavesdropper Eve＇s infor- mation. We then prove the lower bound for the security of the differential phase shift quantum key distribution protocol against a one-pulse attack with Devatak-Winter＇s secret key rate formula.
基金The project is supported by National Natural Science Foundation of China(10371045)Guangdong Provincial Natural Science Foundation of China(000671)National Natural Science Foundation of China(10426015).
文摘This paper considers a two-phase free boundary problem for coupled system including one parabolic equation and two elliptic equations. The problem comes from the discussion of a growth model of self-maintaining protocell in multidimensional case. The local classical solution of the problem with free boundary (?) y = g(x,t) between two domains is being seeked. The local existence and uniqueness of the problem will be proved in multidimensional case.
基金supported by the National Natural Science Foundation of China(Grant Nos.62104180,61974115,11690042,61634005,61974111,12035019,and 61904142)the Fundamental Research Funds for the Central Universities(Grant No.XJS221106)the Key Research and Development Program of Shaanxi,China(Grant No.2020ZDLGY03-05)。
文摘The degradation mechanism of GaN-based near-ultraviolet(NUV,320-400 nm)light emitting diodes(LEDs)with low-indium content under electrical stress is studied from the aspect of defects.A decrease in the optical power and an increase in the leakage current are observed after electrical stress.The defect behaviors are characterized using deep level transient spectroscopy(DLTS)measurement under different filling pulse widths.After stress,the concentration of defects with the energy level of 0.47-0.56 eV increases,accompanied by decrease in the concentration of 0.72-0.84 eV defects.Combing the defect energy level with the increased yellow luminescence in photoluminescence spectra,the device degradation can be attributed to the activation of the gallium vacancy and oxygen related complex defect along dislocation,which was previously passivated with hydrogen.This study reveals the evolution process of defects under electrical stress and their spatial location,laying a foundation for manufacture of GaN-based NUV LEDs with high reliability.
基金Supported by the National Basic Research Programme of China, the National Natural Science Foundation of China under Grant Nos 10674128 and 60121503, the Knowledge Innovation Project and the Hundreds of Talents Programme of Chinese Academy of Sciences, and the Doctoral Foundation of the Education Ministry of China under Grant No 20060358043.
文摘In a recent paper, Sacchi （Phys. Rev. Lett. 96 （2006） 220502） studied the information-disturbance tradeoff in estimating an unknown two-qubit maximally entangled state. In this study, we explore the tradeoff in estimating 13 an unknown three-qubit GHZ state. The optimal estimation process supplies a fidelity of 13/54 and the tradeoff interpolates smoothly between non-informative measurement and optimal estimation process.
基金supported by the National Natural Science Foundation of China(No.61661035)the Natural Science Foundation of Jiangxi Province (No.20192BAB207001)the Aviation Science Foundation (No.201920056001)。
文摘Combining the mutual information theory and the sequential hypothesis testing(SHT)method,a selfadapting radio frequency(RF)stealth signal design method is proposed. The channel information is gained through the radar echo and feeds back to the radar system,and then the radar system adaptively designs the transmission waveform. So the close-loop system is formed. The correlations between these transmission waveforms are decreased because of the adaptive change of these transmission waveforms,and the number of illuminations is reduced for adopting the SHT,which lowers the transmission power of the radar system. The radar system using the new method possesses the RF stealth performance. Aiming at the application of radar automatic target recognition(RATR),experimental simulations show the effectiveness and feasibility of the proposed method.
