Based on a first-order state-vector differential equation representation of Maxwell's equations, an analytical formulation is derived for the equivalent currents on an anisotropic material backed by a metal surfa...Based on a first-order state-vector differential equation representation of Maxwell's equations, an analytical formulation is derived for the equivalent currents on an anisotropic material backed by a metal surface, and the relation between two currents is also considered. These expressions are degenerated into the common forms for some simple cases. This effort will provide the theoretical preparation for the approximate calculation of electromagnetic scattering from a conducting object coated by an anisotropic material.展开更多
A long-standing mystery in the study of Field-Aligned Currents(FACs) has been that: how the currents are generated and why they appear to be much stronger at high altitudes than in the ionosphere. Here we present two ...A long-standing mystery in the study of Field-Aligned Currents(FACs) has been that: how the currents are generated and why they appear to be much stronger at high altitudes than in the ionosphere. Here we present two events of magnetotail FACs observed by the Magnetospheric Multiscale Spacecraft(MMS) on 1 st July and 14 th July 2016, to show how the Substorm Current Wedges(SCW) were formed. The results show that particles were transferred heading towards the Earth during the expansion phase of substorms.The azimuthal flow formed clockwise(counter-clockwise) vortex-like motion, and then generated downward(upward) FACs on the tailward/poleward side of the distorted field with opposite vorticity on their Earthward/equatorward side. We also analyzed the Region 1 FACs observed by the Earth Explorer Swarm spacecraft on 1 st July 2016 and found that they were associated with FACs observed by MMS, although differing by a factor of 10. This difference suggests that either there was the closure of the currents at altitudes above 500 km or the currents were not strictly parallel to B and closed at longitudes away from where they were generated.展开更多
Target modeling and scattering function calculating are important prerequisites and groundwork for the synthetic aperture radar（SAR） imaging simulation.According to the difficult problems that normal methods cannot ...Target modeling and scattering function calculating are important prerequisites and groundwork for the synthetic aperture radar（SAR） imaging simulation.According to the difficult problems that normal methods cannot calculate the scattering function of electrically large object under the condition to wideband,an effective method of improved equivalent edge currents is presented and applied to SAR imaging simulation for the first time.This method improves calculating velocity and has relatively high precision.The concrete steps of applying the method are given.By way of the simulation experiment,the effectiveness of the method is verified.展开更多
Magnetorheological(MR) cell with multi-coil was designed to enlarge the range of controllable transmission torque by increasing the effective length. Individual input current was proposed to maximize its potential for...Magnetorheological(MR) cell with multi-coil was designed to enlarge the range of controllable transmission torque by increasing the effective length. Individual input current was proposed to maximize its potential for reducing power consumption and generating large yield stress. Finite element analysis was performed to analyze magnetic field distribution, based on which a prototype MR cell was fabricated and tested to investigate the performance of various combinations of individual input currents. A good correlation was identified between experimental results and FEA predications. The results show that the power consumption can be reduced to 42.4%, maintaining large transmission torque, by distributing the total current(2 A) to three individual magnetic coils. In addition, optimal results of four input currents considering a multi-objective function are obtained by changing the weighting factor λ. The advantage of this design, such as lower power consumption and more control flexibility, makes it more competitive in engineering applications that require large energy consumption.展开更多
The Fringe Projection Profilometry(FPP)system with a single exposure time or a single projection intensity is limited by the dynamic range of the camera,which can lead to overexposure and underexposure of the image,re...The Fringe Projection Profilometry(FPP)system with a single exposure time or a single projection intensity is limited by the dynamic range of the camera,which can lead to overexposure and underexposure of the image,resulting in point cloud loss or reduced accuracy.To address this issue,unlike the pixel modulation method of projectors,we utilize the characteristics of color projectors where the intensity of the three-channel LED can be controlled independently.We propose a method for separating the projector's three-channel light intensity,combined with a color camera,to achieve single exposure and multi-intensity image acquisition.Further,the crosstalk coefficient is applied to predict the three-channel reflectance of the measured object.By integrating clustering and channel mapping,we establish a pixel-level mapping model between the projector's three-channel current and the camera's three-channel image intensity,which realizes the optimal projection current prediction and the high dynamic range(HDR)image acquisition.The proposed method allows for high-precision three-dimensional(3D)data acquisition of HDR scenes with a single exposure.The effectiveness of this method has been validated through experiments with standard planes and standard steps,showing a significant reduction in mean absolute error(44.6%)compared to existing singleexposure HDR methods.Additionally,the number of images required for acquisition is significantly reduced(by 70.8%)compared to multi-exposure fusion methods.This proposed method has great potential in various FPP-related fields.展开更多
Constructing a photoconductive semiconductor switch (PCSS)-metal coil structure, we discovered anew phenomenon of electromagnetic oscillation in vanadium-compensation semi-insulating (VCSI) PCSS. Here thePCSS responds...Constructing a photoconductive semiconductor switch (PCSS)-metal coil structure, we discovered anew phenomenon of electromagnetic oscillation in vanadium-compensation semi-insulating (VCSI) PCSS. Here thePCSS responds to laser pulse and high-voltage signal while the metal coil generates an oscillating voltage pulseenvelope signal. The generation of this oscillating signal is not related to the input bias voltage of the PCSS, the pulsecircuit components, or the electrode structure of the PCSS, rather it is related to the output characteristic of the PCSS.This physical phenomenon can be explained using the current surge model in photoconducting antenna. Preparingohmic contact electrode on the silicon carbide material forms the PCSS, which generates a large number ofphotogenerated carriers when ultra-fast laser pulses irradiate the surface of the material and Simultaneously applies abias voltage signal between the electrode. At this time inside the PCSS the electric field causes the transient current,radiating electromagnetic wave to the metal coil to generate oscillating signal.展开更多
To know about the radiation effects on the super large array 9 k×9 k CCDs used in a space telescope induced by energetic protons,the experiments of the super large array 9 k×9 k charge coupled devices(CCDs)u...To know about the radiation effects on the super large array 9 k×9 k CCDs used in a space telescope induced by energetic protons,the experiments of the super large array 9 k×9 k charge coupled devices(CCDs)used in the space telescope irradiated by 60 MeV and 100 MeV protons are presented.The samples were exposed by 60 MeV and 100 MeV protons at fluences of 5×10^(9)/cm^(2) and 1×10^(10)/cm^(2),respectively.The degradations of the main performance parameters of the super large array CCDs which are paid special attention to the space telescope are investigated.The full well capacity,mean dark current,and the charge transfer inefficiency(CTI)versus proton fluence are presented,which are tested at very low temperature of-85℃.The annealing tests of 168 h were carried out after proton irradiation.The dark images before and after proton irradiation are also presented to compare the image degradation.The degradation mechanisms of the super large array CCDs irradiated by protons are analyzed.The experimental results show that the main performance parameters of the CCDs are degraded after 60 MeV and 100 MeV protons and the degradations induced by 60 MeV protons are larger than that induced by 100 MeV protons.The experimental results of the super large array CCDs irradiated by protons will provide the basic test data support for orbit life assessment of the space telescope.展开更多
In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ra...In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ratios(λ)were prepared using pulsed electrodeposition in this paper and unidirectional tensile experiments were carried out at room temperature with different currents and their applied directions.The experimental results show that the nanocrystalline Ni foil produces an obvious electroplasticity effect after applying the current field,and when 300<λ<1100,the current weakens the size effect of nanocrystalline Ni foils to a certain extent,and the angle between the current direction and the deformation direction also affects the mechanical response of nanocrystalline Ni foils,and when the angle between the current direction and the deformation direction is 0°,electroplasticity effect is the best,and the current has the most significant effect of abating the size effect of the material.The mechanism of unidirectional tensile deformation of nanocrystalline Ni foils under the effect of pulsed current was analyzed using TEM and TKD.It was found that the applied pulse current increased the activity of the nanocrystalline boundaries,promoted the movement of dislocations,and reduced the tendency of dislocation entanglement.The higher the peak current density and the smaller the angle between the direction of the current and the direction of deformation,the smaller the grain boundary orientation difference,the more dispersed the grain orientation,and the lower the density of geometrically necessary dislocations(GND)in the deformed nanocrystalline foil,the more significant the effect on material plasticity improvement.展开更多
Al-Mg-Mn-Sc-Zr alloys with excellent weldability have emerged as ideal candidates for aerospace applications.Currently,the investigations on the corrosion behavior of alloys under tungsten inert gas(TIG)welding condit...Al-Mg-Mn-Sc-Zr alloys with excellent weldability have emerged as ideal candidates for aerospace applications.Currently,the investigations on the corrosion behavior of alloys under tungsten inert gas(TIG)welding conditions are insufficient.Here,the stress corrosion cracking(SCC)behavior of base metal(BM)and weld zone(WZ)of TIG welded Al-Mg-Mn-Sc-Zr alloys was investigated by using pre-cracked compact tensile samples immersed in 3.5%NaCl solution.The direct current potential drop(DCPD)method was used to record the crack propagation.The microstructure and fracture morphology of different regions of TIG welded joints were studied by SEM,EBSD and TEM,and the SCC crack propagation mechanism of BM and WZ was analyzed.The results demonstrated that the critical stress intensity factor for stress corrosion cracking(K_(ⅠSCC))of BM and WZ was 7.05 MPa·m_(1/2) and 11.79 MPa·m_(1/2),respectively.Then,the crack propagation rate of BM was faster than that of WZ,and BM was more susceptible to SCC than WZ.Additionally,the fracture mode of the BM mainly exhibited transgranular fracture,while the fracture mode of the WZ mainly exhibited intergranular and transgranular mixed fracture.Moreover,SCC crack propagation was attributed to the combined effect of anodic dissolution and hydrogen embrittlement.This study will provide experimental and theoretical basis for the wide application of TIG welded Al-Mg-Mn-Sc-Zr alloys in aerospace.展开更多
The lattice-matched XBn structures of InAsSb,grown on GaSb substrates,exhibit high crystal quali⁃ty,and can achieve extremely low dark currents at high operating temperatures(HOT).Its superior performance is attribute...The lattice-matched XBn structures of InAsSb,grown on GaSb substrates,exhibit high crystal quali⁃ty,and can achieve extremely low dark currents at high operating temperatures(HOT).Its superior performance is attributed to the unipolar barrier,which blocks the majority carriers while allowing unhindered hole transport.To further explore the energy band and carrier transport mechanisms of the XBn unipolar barrier structure,this pa⁃per systematically investigates the influence of doping on the dark current,photocurrent,and tunneling character⁃istics of InAsSb photodetectors in the PBn structure.Three high-quality InAsSb samples with unintentionally doped absorption layers(AL)were prepared,with varying p-type doping concentrations in the GaSb contact layer(CL)and the AlAsSb barrier layer(BL).As the p-type doping concentration in the CL increased,the device’s turn-on bias voltage also increased,and p-type doping in the BL led to tunneling occurring at lower bias voltages.For the sample with UID BL,which exhibited an extremely low dark current of 5×10^(-6) A/cm^(2).The photocurrent characteristics were well-fitted using the back-to-back diode model,revealing the presence of two opposing space charge regions on either side of the BL.展开更多
With the analysis of experiment and theory on GaN HEMT devices under DC sweep,an improved model for kink effect based on advanced SPICE model for high electron mobility transistors(ASM-HEMT)is pro⁃posed,considering th...With the analysis of experiment and theory on GaN HEMT devices under DC sweep,an improved model for kink effect based on advanced SPICE model for high electron mobility transistors(ASM-HEMT)is pro⁃posed,considering the relationship between the drain/gate-source voltage and kink effect.The improved model can not only accurately describe the trend of the drain-source current with the current collapse and kink effect,but also precisely fit different values of drain-source voltages at which the kink effect occurs under different gatesource voltages.Furthermore,it well characterizes the DC characteristics of GaN devices in the full operating range,with the fitting error less than 3%.To further verify the accuracy and convergence of the improved model,a load-pull system is built in ADS.The simulated result shows that although both the original ASM-HEMT and the improved model predict the output power for the maximum power matching of GaN devices well,the im⁃proved model predicts the power-added efficiency for the maximum efficiency matching more accurately,with 4%improved.展开更多
In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperatur...In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperature swing can be equivalent to reducing maximum instantaneous phase copper loss in this paper.First,a two-level optimization aiming at minimizing maximum instantaneous phase copper loss at each electrical angle is proposed.Then,the optimization is transformed to a singlelevel optimization by introducing the auxiliary variable for easy solving.Considering that singleobjective optimization trades a great total copper loss for a small reduction of maximum phase copper loss,the optimization considering both instantaneous total copper loss and maximum phase copper loss is proposed,which has the same performance of temperature swing reduction but with lower total loss.In this way,the proposed control scheme can reduce maximum junction temperature by 11%.Both simulation and experimental results are presented to prove the effectiveness and superiority of the proposed control scheme for low-frequency temperature swing reduction.展开更多
SnO_(2)is used as electrode material with excellent properties,but it has some disadvantages such as slow reaction kinetics,low inherent conductivity and complex preparation process.Here,SnO_(2)@carbon nanotubes(SnO_(...SnO_(2)is used as electrode material with excellent properties,but it has some disadvantages such as slow reaction kinetics,low inherent conductivity and complex preparation process.Here,SnO_(2)@carbon nanotubes(SnO_(2)@CNTs)is synthesized through an efficient method of one-pot alternating current electrochemical dispersion.By using heat treatment at 400℃,the SnO_(2)@CNTs-400 composite material with abundant mesoporous structure is obtained,while the crystal particles are grown,and a strong bonding effect is formed with CNTs via powerful Sn-O-C bond.Benefiting from the introduction of high electrical conductivity CNTs and outstanding structural characteristics,as prepared composite material(SnO_(2)@CNTs-400)exhibit enhanced diffusion dynamics,lithium-ion transmission rate and structural steadiness.The specific capacity of SnO_(2)@CNTs and SnO_(2)@CNTs-400 as anodes for lithium-ion batteries can reach 690.2 mA·h/g and 836.5 mA·h/g,respectively,after 100 cycles at 0.5 A/g.The abundant chemical bonds and porous structure can be formed in composite via alternating current synthesis method,which takes significant in improving electrochemical properties.展开更多
In construction of a high current heated hot-tube ion-source, the design of heat shield structure, the optimization of the current input pole and the structure of the heat dissipation are discussed. The heat test of t...In construction of a high current heated hot-tube ion-source, the design of heat shield structure, the optimization of the current input pole and the structure of the heat dissipation are discussed. The heat test of this ion-source is also mentioned and discussed.展开更多
本文从专家推荐网站入手对学科网站进行研究,以气象学为例,通过检索ISI Current Contents Connect数据库,对学科网站的地理分布、语种分布、信息来源、出版者及关键词进行统计分析,总结出学科网站的一些特点。最后对目前学科网络信息资...本文从专家推荐网站入手对学科网站进行研究,以气象学为例,通过检索ISI Current Contents Connect数据库,对学科网站的地理分布、语种分布、信息来源、出版者及关键词进行统计分析,总结出学科网站的一些特点。最后对目前学科网络信息资源研究提出了自己的看法。展开更多
As a solution to the breaking of pipeline under high axial force,carbon fiber composite pipe with low density and high intensity is applied to deep-sea mining transporting system.Based on the fact that the transportin...As a solution to the breaking of pipeline under high axial force,carbon fiber composite pipe with low density and high intensity is applied to deep-sea mining transporting system.Based on the fact that the transporting pipe is under the forces of gravity,inner liquid,buoyancy as well as hydrodynamic force,geometric nonlinear finite element theory has been applied to analyzing the transporting system.Conclusions can be drawn as follows.Under the interaction of waves and currents,node forces FX and FZ acted by the transporting pipe on the mining vehicle are less than 2 kN,which indicates that waves and currents have little influence on the spatial shape of the transporting pipe and the mining vehicle movement.On the other hand,the horizontal force acting on the mining ship could be as large as 106 830 N,which has great influence on the mining system.展开更多
文摘Based on a first-order state-vector differential equation representation of Maxwell's equations, an analytical formulation is derived for the equivalent currents on an anisotropic material backed by a metal surface, and the relation between two currents is also considered. These expressions are degenerated into the common forms for some simple cases. This effort will provide the theoretical preparation for the approximate calculation of electromagnetic scattering from a conducting object coated by an anisotropic material.
基金Supported by National Natural Science Foundation of China(41874190,41231066)
文摘A long-standing mystery in the study of Field-Aligned Currents(FACs) has been that: how the currents are generated and why they appear to be much stronger at high altitudes than in the ionosphere. Here we present two events of magnetotail FACs observed by the Magnetospheric Multiscale Spacecraft(MMS) on 1 st July and 14 th July 2016, to show how the Substorm Current Wedges(SCW) were formed. The results show that particles were transferred heading towards the Earth during the expansion phase of substorms.The azimuthal flow formed clockwise(counter-clockwise) vortex-like motion, and then generated downward(upward) FACs on the tailward/poleward side of the distorted field with opposite vorticity on their Earthward/equatorward side. We also analyzed the Region 1 FACs observed by the Earth Explorer Swarm spacecraft on 1 st July 2016 and found that they were associated with FACs observed by MMS, although differing by a factor of 10. This difference suggests that either there was the closure of the currents at altitudes above 500 km or the currents were not strictly parallel to B and closed at longitudes away from where they were generated.
基金supported by the National Natural Science Foundation of China(60871070)
文摘Target modeling and scattering function calculating are important prerequisites and groundwork for the synthetic aperture radar（SAR） imaging simulation.According to the difficult problems that normal methods cannot calculate the scattering function of electrically large object under the condition to wideband,an effective method of improved equivalent edge currents is presented and applied to SAR imaging simulation for the first time.This method improves calculating velocity and has relatively high precision.The concrete steps of applying the method are given.By way of the simulation experiment,the effectiveness of the method is verified.
基金Projects(51175265,51305207)supported by the National Natural Science Foundation of China
文摘Magnetorheological(MR) cell with multi-coil was designed to enlarge the range of controllable transmission torque by increasing the effective length. Individual input current was proposed to maximize its potential for reducing power consumption and generating large yield stress. Finite element analysis was performed to analyze magnetic field distribution, based on which a prototype MR cell was fabricated and tested to investigate the performance of various combinations of individual input currents. A good correlation was identified between experimental results and FEA predications. The results show that the power consumption can be reduced to 42.4%, maintaining large transmission torque, by distributing the total current(2 A) to three individual magnetic coils. In addition, optimal results of four input currents considering a multi-objective function are obtained by changing the weighting factor λ. The advantage of this design, such as lower power consumption and more control flexibility, makes it more competitive in engineering applications that require large energy consumption.
文摘The Fringe Projection Profilometry(FPP)system with a single exposure time or a single projection intensity is limited by the dynamic range of the camera,which can lead to overexposure and underexposure of the image,resulting in point cloud loss or reduced accuracy.To address this issue,unlike the pixel modulation method of projectors,we utilize the characteristics of color projectors where the intensity of the three-channel LED can be controlled independently.We propose a method for separating the projector's three-channel light intensity,combined with a color camera,to achieve single exposure and multi-intensity image acquisition.Further,the crosstalk coefficient is applied to predict the three-channel reflectance of the measured object.By integrating clustering and channel mapping,we establish a pixel-level mapping model between the projector's three-channel current and the camera's three-channel image intensity,which realizes the optimal projection current prediction and the high dynamic range(HDR)image acquisition.The proposed method allows for high-precision three-dimensional(3D)data acquisition of HDR scenes with a single exposure.The effectiveness of this method has been validated through experiments with standard planes and standard steps,showing a significant reduction in mean absolute error(44.6%)compared to existing singleexposure HDR methods.Additionally,the number of images required for acquisition is significantly reduced(by 70.8%)compared to multi-exposure fusion methods.This proposed method has great potential in various FPP-related fields.
基金supported by Major Projects of Shanxi Province (202101030201001)。
文摘Constructing a photoconductive semiconductor switch (PCSS)-metal coil structure, we discovered anew phenomenon of electromagnetic oscillation in vanadium-compensation semi-insulating (VCSI) PCSS. Here thePCSS responds to laser pulse and high-voltage signal while the metal coil generates an oscillating voltage pulseenvelope signal. The generation of this oscillating signal is not related to the input bias voltage of the PCSS, the pulsecircuit components, or the electrode structure of the PCSS, rather it is related to the output characteristic of the PCSS.This physical phenomenon can be explained using the current surge model in photoconducting antenna. Preparingohmic contact electrode on the silicon carbide material forms the PCSS, which generates a large number ofphotogenerated carriers when ultra-fast laser pulses irradiate the surface of the material and Simultaneously applies abias voltage signal between the electrode. At this time inside the PCSS the electric field causes the transient current,radiating electromagnetic wave to the metal coil to generate oscillating signal.
基金The National Science Foundation of China(U2167208,11875223)Natural Science Basic Research Program of Shaanxi(2024JC-JCQN)The Foundation of State Key Laboratory of China(NKLIPR2320)。
文摘To know about the radiation effects on the super large array 9 k×9 k CCDs used in a space telescope induced by energetic protons,the experiments of the super large array 9 k×9 k charge coupled devices(CCDs)used in the space telescope irradiated by 60 MeV and 100 MeV protons are presented.The samples were exposed by 60 MeV and 100 MeV protons at fluences of 5×10^(9)/cm^(2) and 1×10^(10)/cm^(2),respectively.The degradations of the main performance parameters of the super large array CCDs which are paid special attention to the space telescope are investigated.The full well capacity,mean dark current,and the charge transfer inefficiency(CTI)versus proton fluence are presented,which are tested at very low temperature of-85℃.The annealing tests of 168 h were carried out after proton irradiation.The dark images before and after proton irradiation are also presented to compare the image degradation.The degradation mechanisms of the super large array CCDs irradiated by protons are analyzed.The experimental results show that the main performance parameters of the CCDs are degraded after 60 MeV and 100 MeV protons and the degradations induced by 60 MeV protons are larger than that induced by 100 MeV protons.The experimental results of the super large array CCDs irradiated by protons will provide the basic test data support for orbit life assessment of the space telescope.
基金Project(51975167)supported by the National Natural Science Foundation of China。
文摘In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ratios(λ)were prepared using pulsed electrodeposition in this paper and unidirectional tensile experiments were carried out at room temperature with different currents and their applied directions.The experimental results show that the nanocrystalline Ni foil produces an obvious electroplasticity effect after applying the current field,and when 300<λ<1100,the current weakens the size effect of nanocrystalline Ni foils to a certain extent,and the angle between the current direction and the deformation direction also affects the mechanical response of nanocrystalline Ni foils,and when the angle between the current direction and the deformation direction is 0°,electroplasticity effect is the best,and the current has the most significant effect of abating the size effect of the material.The mechanism of unidirectional tensile deformation of nanocrystalline Ni foils under the effect of pulsed current was analyzed using TEM and TKD.It was found that the applied pulse current increased the activity of the nanocrystalline boundaries,promoted the movement of dislocations,and reduced the tendency of dislocation entanglement.The higher the peak current density and the smaller the angle between the direction of the current and the direction of deformation,the smaller the grain boundary orientation difference,the more dispersed the grain orientation,and the lower the density of geometrically necessary dislocations(GND)in the deformed nanocrystalline foil,the more significant the effect on material plasticity improvement.
基金Project (2023GK1080) supported by the Major Special Projects of Hunan Province of China。
文摘Al-Mg-Mn-Sc-Zr alloys with excellent weldability have emerged as ideal candidates for aerospace applications.Currently,the investigations on the corrosion behavior of alloys under tungsten inert gas(TIG)welding conditions are insufficient.Here,the stress corrosion cracking(SCC)behavior of base metal(BM)and weld zone(WZ)of TIG welded Al-Mg-Mn-Sc-Zr alloys was investigated by using pre-cracked compact tensile samples immersed in 3.5%NaCl solution.The direct current potential drop(DCPD)method was used to record the crack propagation.The microstructure and fracture morphology of different regions of TIG welded joints were studied by SEM,EBSD and TEM,and the SCC crack propagation mechanism of BM and WZ was analyzed.The results demonstrated that the critical stress intensity factor for stress corrosion cracking(K_(ⅠSCC))of BM and WZ was 7.05 MPa·m_(1/2) and 11.79 MPa·m_(1/2),respectively.Then,the crack propagation rate of BM was faster than that of WZ,and BM was more susceptible to SCC than WZ.Additionally,the fracture mode of the BM mainly exhibited transgranular fracture,while the fracture mode of the WZ mainly exhibited intergranular and transgranular mixed fracture.Moreover,SCC crack propagation was attributed to the combined effect of anodic dissolution and hydrogen embrittlement.This study will provide experimental and theoretical basis for the wide application of TIG welded Al-Mg-Mn-Sc-Zr alloys in aerospace.
基金Supported by the Candidate Talents Training Fund of Yunnan Province(202205AC160054)the National Natural Science Foundation of China(62174156)。
文摘The lattice-matched XBn structures of InAsSb,grown on GaSb substrates,exhibit high crystal quali⁃ty,and can achieve extremely low dark currents at high operating temperatures(HOT).Its superior performance is attributed to the unipolar barrier,which blocks the majority carriers while allowing unhindered hole transport.To further explore the energy band and carrier transport mechanisms of the XBn unipolar barrier structure,this pa⁃per systematically investigates the influence of doping on the dark current,photocurrent,and tunneling character⁃istics of InAsSb photodetectors in the PBn structure.Three high-quality InAsSb samples with unintentionally doped absorption layers(AL)were prepared,with varying p-type doping concentrations in the GaSb contact layer(CL)and the AlAsSb barrier layer(BL).As the p-type doping concentration in the CL increased,the device’s turn-on bias voltage also increased,and p-type doping in the BL led to tunneling occurring at lower bias voltages.For the sample with UID BL,which exhibited an extremely low dark current of 5×10^(-6) A/cm^(2).The photocurrent characteristics were well-fitted using the back-to-back diode model,revealing the presence of two opposing space charge regions on either side of the BL.
基金Supported by the National Key R&D Program of China(2022YFF0707800,2022YFF0707801)Primary Research&Development Plan of Jiangsu Province(BE2022070,BE2022070-2)。
文摘With the analysis of experiment and theory on GaN HEMT devices under DC sweep,an improved model for kink effect based on advanced SPICE model for high electron mobility transistors(ASM-HEMT)is pro⁃posed,considering the relationship between the drain/gate-source voltage and kink effect.The improved model can not only accurately describe the trend of the drain-source current with the current collapse and kink effect,but also precisely fit different values of drain-source voltages at which the kink effect occurs under different gatesource voltages.Furthermore,it well characterizes the DC characteristics of GaN devices in the full operating range,with the fitting error less than 3%.To further verify the accuracy and convergence of the improved model,a load-pull system is built in ADS.The simulated result shows that although both the original ASM-HEMT and the improved model predict the output power for the maximum power matching of GaN devices well,the im⁃proved model predicts the power-added efficiency for the maximum efficiency matching more accurately,with 4%improved.
基金supported by the National Natural Science Foundation of China(No.62271109)。
文摘In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperature swing can be equivalent to reducing maximum instantaneous phase copper loss in this paper.First,a two-level optimization aiming at minimizing maximum instantaneous phase copper loss at each electrical angle is proposed.Then,the optimization is transformed to a singlelevel optimization by introducing the auxiliary variable for easy solving.Considering that singleobjective optimization trades a great total copper loss for a small reduction of maximum phase copper loss,the optimization considering both instantaneous total copper loss and maximum phase copper loss is proposed,which has the same performance of temperature swing reduction but with lower total loss.In this way,the proposed control scheme can reduce maximum junction temperature by 11%.Both simulation and experimental results are presented to prove the effectiveness and superiority of the proposed control scheme for low-frequency temperature swing reduction.
基金Project(2023JЛ10041)supported by the Distinguished Young Scholar Fund Project of Hunan Province Natural Science Foundation,ChinaProject(22A0114)supported by the Hunan Provincial Education Office Foundation of China+2 种基金Projects(GX-ZD20211004,GX-ZD20221007)supported by the Science and Technology Program of Xiangtan,ChinaProject(R24-5979269037)supported by the RSC Research Fund Grout,EnglandProject(S202310530037X)supported by the National College Students Innovative Experimental Program Funding Project,China。
文摘SnO_(2)is used as electrode material with excellent properties,but it has some disadvantages such as slow reaction kinetics,low inherent conductivity and complex preparation process.Here,SnO_(2)@carbon nanotubes(SnO_(2)@CNTs)is synthesized through an efficient method of one-pot alternating current electrochemical dispersion.By using heat treatment at 400℃,the SnO_(2)@CNTs-400 composite material with abundant mesoporous structure is obtained,while the crystal particles are grown,and a strong bonding effect is formed with CNTs via powerful Sn-O-C bond.Benefiting from the introduction of high electrical conductivity CNTs and outstanding structural characteristics,as prepared composite material(SnO_(2)@CNTs-400)exhibit enhanced diffusion dynamics,lithium-ion transmission rate and structural steadiness.The specific capacity of SnO_(2)@CNTs and SnO_(2)@CNTs-400 as anodes for lithium-ion batteries can reach 690.2 mA·h/g and 836.5 mA·h/g,respectively,after 100 cycles at 0.5 A/g.The abundant chemical bonds and porous structure can be formed in composite via alternating current synthesis method,which takes significant in improving electrochemical properties.
文摘In construction of a high current heated hot-tube ion-source, the design of heat shield structure, the optimization of the current input pole and the structure of the heat dissipation are discussed. The heat test of this ion-source is also mentioned and discussed.
基金Project(50975290) supported by the National Natural Science Foundation of ChinaProject(2011QNZT057) supported by the Basic Operational Cost of Special Research Funding of Central Universities in ChinaProject(11JJ5028) supported by Hunan Provincial Natural Science Foundation,China
文摘As a solution to the breaking of pipeline under high axial force,carbon fiber composite pipe with low density and high intensity is applied to deep-sea mining transporting system.Based on the fact that the transporting pipe is under the forces of gravity,inner liquid,buoyancy as well as hydrodynamic force,geometric nonlinear finite element theory has been applied to analyzing the transporting system.Conclusions can be drawn as follows.Under the interaction of waves and currents,node forces FX and FZ acted by the transporting pipe on the mining vehicle are less than 2 kN,which indicates that waves and currents have little influence on the spatial shape of the transporting pipe and the mining vehicle movement.On the other hand,the horizontal force acting on the mining ship could be as large as 106 830 N,which has great influence on the mining system.
