In determining the orbits of low Earth orbit （LEO） satellites using spaceborne GPS, the errors caused by receiver antenna phase center offset （PCO） and phase center variations （PCVs） are gradually becoming a maj...In determining the orbits of low Earth orbit （LEO） satellites using spaceborne GPS, the errors caused by receiver antenna phase center offset （PCO） and phase center variations （PCVs） are gradually becoming a major limiting factor for continued improvements to accuracy. Shiyan 3, a small satellite mission for space technology experimentation and climate exploration, was developed by China and launched on November 5, 2008. The dual-frequency GPS receiver payload delivers 1 Hz data and provides the basis for precise orbit determination within the range of a few centimeters. The antenna PCO and PCV error characteristics and the principles influencing orbit determination are analyzed. The feasibility of PCO and PCV estimation and compensation in different directions is demonstrated through simulation and in-flight tests. The values of receiver antenna PCO and PCVs for Gravity Recovery and Climate Experiment （GRACE） and Shiyan 3 satellites are estimated from one month of data. A large and stable antenna PCO error, reaching up to 10.34 cm in the z-direction, is found with the Shiyan 3 satellite. The PCVs on the Shiyan 3 satellite are estimated and reach up to 3.0 cm, which is slightly larger than that of GRACE satellites. Orbit validation clearly improved with independent k-band ranging （KBR） and satellite laser ranging （SLR） measurements. For GRACE satellites, the average root mean square （RMS） of KBR residuals improved from 1.01 cm to 0.88 cm. For the Shiyan 3 satellite, the average RMS of SLR residuals improved from 4.95 cm to 4.06 cm.展开更多
With the explosive growth of surveillance video data,browsing videos quickly and effectively has become an urgent problem.Video key frame extraction has received widespread attention as an effective solution.However,a...With the explosive growth of surveillance video data,browsing videos quickly and effectively has become an urgent problem.Video key frame extraction has received widespread attention as an effective solution.However,accurately capturing the local motion state changes of moving objects in the video is still challenging in key frame extraction.The target center offset can reflect the change of its motion state.This observation proposed a novel key frame extraction method based on moving objects center offset in this paper.The proposed method utilizes the center offset to obtain the global and local motion state information of moving objects,and meanwhile,selects the video frame where the center offset curve changes suddenly as the key frame.Such processing effectively overcomes the inaccuracy of traditional key frame extraction methods.Initially,extracting the center point of each frame.Subsequently,calculating the center point offset of each frame and forming the center offset curve by connecting the center offset of each frame.Finally,extracting candidate key frames and optimizing them to generate final key frames.The experimental results demonstrate that the proposed method outperforms contrast methods to capturing the local motion state changes of moving objects.展开更多
A scanning and uniform array architecture with large spacing,low complexity and high scalability is presented for high integration massive array applications.It is constructed by offset phase center elements arranged ...A scanning and uniform array architecture with large spacing,low complexity and high scalability is presented for high integration massive array applications.It is constructed by offset phase center elements arranged in a uniform and regular way,but its spacing can be larger than that of traditional arrays.An ideal model of the offset phase center element is established and its far-field distribution is derived.To suppress grating lobes,the phase center of any element is designed to be movable without changing its physical position.Using genetic algorithm(GA),a new constraint condition limiting the number of phase center changes is proposed to solve the objective function of the minimum values of grating lobes(GLs)and side lobes(SLs).It is shown that the optimal results can be achieved by two changes of phase centers.A multimode circular patch is developed and designed,and characteristics of the offset phase center are analyzed and verified.A prototype array of 12×12 offset phase center elements is implemented based on multi-mode circular patches.Full wave simulation results of radiation patterns show that the level of grating lobes is suppressed at least 7dB with 1.12λ spacing,while the scanning angle is 20°.展开更多
The correction for antenna phase center is considered in processing Global Positioning System （GPS） data collected from a network of GPS ultra-short baselines. Compared with the leveling measurements, the GPS result...The correction for antenna phase center is considered in processing Global Positioning System （GPS） data collected from a network of GPS ultra-short baselines. Compared with the leveling measurements, the GPS results show that the relative vertical offsets for the pairs of GPS receiver antenna phase centers still exist, although absolute calibration of the antenna phase center variations （PCVs） has been considered. With respect to the TPS CR.G3 antenna, the relative vertical offset for the LEI AT504 antenna is 8.4 mm, the offset for the ASH701945C_M antenna is 5.5 mm, and those for the ASHY00936E_C and ASH701945B_M antennas are approximately between 2 mm and -3 mm. The relative offsets for the same type of antennas are approximately 1 mm. By correcting the absolute PCVs, the existing relative offset becomes negligible for horizontal positioning.展开更多
对红外光学系统的中心偏差开展分析,构建中心偏差分析流程,并提出相应的装调方法。首先,对红外光学系统的中心偏差的成因初步解构为光学元件的子午和弧矢方向的倾斜变化与平移变化,并将该变化量通过公差的形式,与光学性能指标——调制...对红外光学系统的中心偏差开展分析,构建中心偏差分析流程,并提出相应的装调方法。首先,对红外光学系统的中心偏差的成因初步解构为光学元件的子午和弧矢方向的倾斜变化与平移变化,并将该变化量通过公差的形式,与光学性能指标——调制传递函数(Modulation Transfer Function,MTF)以及光轴漂移量建立关系,得到各光学元件公差引起的空间姿态与理想系统光轴之间的差异,并根据差异的大小,评估各光学元件对MTF的贡献度以及对系统光轴的影响程度,建立各光学元件的灵敏度表。根据各光学元件的灵敏度结果,以系统指标要求的光轴漂移量为分析点,利用蒙特卡罗(Monte Carlo)计算引擎对各光学元件以及组件的各种姿态组合进行计算,得出光学元件在满足指标要求下的公差限。根据以上的分析结果,提出基于光轴偏移校正和光学元件位置调整的调校方法,该方法利用中心偏测量仪实时监测敏感元件的中心偏差,并通过有效的光轴偏移校正和元件位置调整,使光学系统的中心对准光轴。通过实验验证,证明了该调校方法能够有效减小中心偏差,提高红外光学系统的性能和图像质量。展开更多
Durning the design process of hydrostatic rotary worktable,the processing and assembly tolerance,（the offset of worktable and the gap of the oil film’s thickness）is ignored.But it will cause that the real bearing o...Durning the design process of hydrostatic rotary worktable,the processing and assembly tolerance,（the offset of worktable and the gap of the oil film’s thickness）is ignored.But it will cause that the real bearing of oil pocket deviates from the initial design value,and then the performance of rotary worktable will be reduced significantly.Up to now,no effort is found toward the research of influence of the processing and assembly tolerance on the performance of the rotary worktable.So the hydrostatic oil film is assumed as the elastomer in this paper,and then the bearing capacity of the oil pocket is studied with and without the mass offset of the worktable by taking an expression between the bearing capacity and the oil film’s thickness of the oil pocket as the deform compatibility equation.The influence of the processing tolerance of the oil sealing belt’s gap on the bearing capacity of the oil pocket is analyzed.In the light of the liquid hydrostatic worktable of Gantry Moving Milling Center using on the scene,the oil pocket’s pressure of the worktable is tested using Rotary Worktable Test System under the circumstance of the mass offset of the worktable and the gap tolerance of the oil sealing belt,and then the equivalent offset of worktable,the average pressure of the oil pocket and the actual thickness of the oil film are analyzed respectively.The test results show that the bearing capacity component of the oil pocket caused by G is consistent,and the component caused by M is relative to the position of the oil pocket.When the oil sealing belt’s gap is larger than the theoretical value,the bearing capacity of the oil pocket is smaller than the others;whereas the bearing capacity of the oil pocket is larger than the others.The maximum and minimum equivalent offsets are 0.256 4 mm and 0.047 5 mm,respectively,and the average oil pocket pressure varies from 0.345 MPa to 0.460 MPa,the maximum and minimum value of the actual oil film thickness are 109.976？m（No.7 oil pocket）and 93.467？m（No.10 oil pocket）,respectively.The research results can be used to detect the offset of the worktable and the actual thickness of the oil film under processing and assembly tolerance,and provides a basis way for detecting the processing and assembly tolerance of rotary worktable signing reasonably of Gantry Moving Milling Center.展开更多
目的:使用CT联合Mimics软件测量全髋关节置换术(total hip arthroplasty,THA)后股骨偏心距(femoral offset,FO)、旋转中心高度(rotation center height,RCH)与双下肢长度差(lower leg length discrepancy,LLD),并探讨THA后FO、RCH与LLD...目的:使用CT联合Mimics软件测量全髋关节置换术(total hip arthroplasty,THA)后股骨偏心距(femoral offset,FO)、旋转中心高度(rotation center height,RCH)与双下肢长度差(lower leg length discrepancy,LLD),并探讨THA后FO、RCH与LLD的关系。方法:回顾性分析2020年10月至2022年6月符合标准的40例行单侧THA的患者,其中男21例,女19例;年龄30~81(58.90±14.13)岁;身体质量指数(body mass index,BMI)为17.3~31.5(25.3±3.4)kg·m^(-2);左侧18例,右侧22例。诊断为股骨头坏死30例(FicatⅣ期),髋关节骨性关节炎2例(TünnisⅢ期),发育性髋关节脱位合并终末期骨关节炎2例(CroweⅢ期),股骨颈骨折6例(GardenⅣ期)。术前、术后拍摄骨盆CT三维重建,经Mimics软件处理后建立三维重建模型,在模型上对FO、RCH、LLD进行测量。结果:术后双侧FO差值与LLD呈正相关性(r=0.744,P<0.001);将FO重建组与偏心距未重建组进行卡方检验得出:FO重建组下肢等长率高于FO未重建组(χ^(2)=6.320,P=0.012)。术后双侧RCH差值与LLD呈负相关性(r=-0.877,P<0.001);双侧FO差值及双侧RCH差值与术后LLD之间存在线性关系,且满足线性回归方程:术后LLD=0.038x-0.099y+0.257(x为术后双侧FO差值;y为术后双侧RCH差值;单位为cm),F=77.993,R2=0.808,P=0.009。结论:THA术后LLD随着FO的增大而增大,随着RCH增大而减小;重建FO更易获得下肢等长效果。THA术后双侧FO差值及双侧RCH差值与LLD之间存在线性关系,回归方程可为判断LLD提供一种理论参考。展开更多
基金co-supported by the National Natural Science Foundation of China (Nos.61370013 and 91438202)the High Resolution Earth Observation System Major Special Project Youth Innovation Foundation of China (No.GFZX04060103)
文摘In determining the orbits of low Earth orbit （LEO） satellites using spaceborne GPS, the errors caused by receiver antenna phase center offset （PCO） and phase center variations （PCVs） are gradually becoming a major limiting factor for continued improvements to accuracy. Shiyan 3, a small satellite mission for space technology experimentation and climate exploration, was developed by China and launched on November 5, 2008. The dual-frequency GPS receiver payload delivers 1 Hz data and provides the basis for precise orbit determination within the range of a few centimeters. The antenna PCO and PCV error characteristics and the principles influencing orbit determination are analyzed. The feasibility of PCO and PCV estimation and compensation in different directions is demonstrated through simulation and in-flight tests. The values of receiver antenna PCO and PCVs for Gravity Recovery and Climate Experiment （GRACE） and Shiyan 3 satellites are estimated from one month of data. A large and stable antenna PCO error, reaching up to 10.34 cm in the z-direction, is found with the Shiyan 3 satellite. The PCVs on the Shiyan 3 satellite are estimated and reach up to 3.0 cm, which is slightly larger than that of GRACE satellites. Orbit validation clearly improved with independent k-band ranging （KBR） and satellite laser ranging （SLR） measurements. For GRACE satellites, the average root mean square （RMS） of KBR residuals improved from 1.01 cm to 0.88 cm. For the Shiyan 3 satellite, the average RMS of SLR residuals improved from 4.95 cm to 4.06 cm.
基金This work was supported by the National Nature Science Foundation of China(Grant No.61702347,61772225)Natural Science Foundation of Hebei Province(Grant No.F2017210161).
文摘With the explosive growth of surveillance video data,browsing videos quickly and effectively has become an urgent problem.Video key frame extraction has received widespread attention as an effective solution.However,accurately capturing the local motion state changes of moving objects in the video is still challenging in key frame extraction.The target center offset can reflect the change of its motion state.This observation proposed a novel key frame extraction method based on moving objects center offset in this paper.The proposed method utilizes the center offset to obtain the global and local motion state information of moving objects,and meanwhile,selects the video frame where the center offset curve changes suddenly as the key frame.Such processing effectively overcomes the inaccuracy of traditional key frame extraction methods.Initially,extracting the center point of each frame.Subsequently,calculating the center point offset of each frame and forming the center offset curve by connecting the center offset of each frame.Finally,extracting candidate key frames and optimizing them to generate final key frames.The experimental results demonstrate that the proposed method outperforms contrast methods to capturing the local motion state changes of moving objects.
基金This work was supported by National Natural Science Foundation of China(No.U19B2028).
文摘A scanning and uniform array architecture with large spacing,low complexity and high scalability is presented for high integration massive array applications.It is constructed by offset phase center elements arranged in a uniform and regular way,but its spacing can be larger than that of traditional arrays.An ideal model of the offset phase center element is established and its far-field distribution is derived.To suppress grating lobes,the phase center of any element is designed to be movable without changing its physical position.Using genetic algorithm(GA),a new constraint condition limiting the number of phase center changes is proposed to solve the objective function of the minimum values of grating lobes(GLs)and side lobes(SLs).It is shown that the optimal results can be achieved by two changes of phase centers.A multimode circular patch is developed and designed,and characteristics of the offset phase center are analyzed and verified.A prototype array of 12×12 offset phase center elements is implemented based on multi-mode circular patches.Full wave simulation results of radiation patterns show that the level of grating lobes is suppressed at least 7dB with 1.12λ spacing,while the scanning angle is 20°.
基金supported by the Science for Earthquake Resilience(XH14070Y,XH15064Y)the China NationalSpecial Fund for Earthquake Scientific Research in Public Interest(201208009)
文摘The correction for antenna phase center is considered in processing Global Positioning System （GPS） data collected from a network of GPS ultra-short baselines. Compared with the leveling measurements, the GPS results show that the relative vertical offsets for the pairs of GPS receiver antenna phase centers still exist, although absolute calibration of the antenna phase center variations （PCVs） has been considered. With respect to the TPS CR.G3 antenna, the relative vertical offset for the LEI AT504 antenna is 8.4 mm, the offset for the ASH701945C_M antenna is 5.5 mm, and those for the ASHY00936E_C and ASH701945B_M antennas are approximately between 2 mm and -3 mm. The relative offsets for the same type of antennas are approximately 1 mm. By correcting the absolute PCVs, the existing relative offset becomes negligible for horizontal positioning.
文摘对红外光学系统的中心偏差开展分析,构建中心偏差分析流程,并提出相应的装调方法。首先,对红外光学系统的中心偏差的成因初步解构为光学元件的子午和弧矢方向的倾斜变化与平移变化,并将该变化量通过公差的形式,与光学性能指标——调制传递函数(Modulation Transfer Function,MTF)以及光轴漂移量建立关系,得到各光学元件公差引起的空间姿态与理想系统光轴之间的差异,并根据差异的大小,评估各光学元件对MTF的贡献度以及对系统光轴的影响程度,建立各光学元件的灵敏度表。根据各光学元件的灵敏度结果,以系统指标要求的光轴漂移量为分析点,利用蒙特卡罗(Monte Carlo)计算引擎对各光学元件以及组件的各种姿态组合进行计算,得出光学元件在满足指标要求下的公差限。根据以上的分析结果,提出基于光轴偏移校正和光学元件位置调整的调校方法,该方法利用中心偏测量仪实时监测敏感元件的中心偏差,并通过有效的光轴偏移校正和元件位置调整,使光学系统的中心对准光轴。通过实验验证,证明了该调校方法能够有效减小中心偏差,提高红外光学系统的性能和图像质量。
基金Supported by National Natural Science Foundation of China(Grant No.51075348)Hebei Provincial Natural Science Foundation of China(Grant No.E2011203151)Research Fund for Doctoral Program of Higher Education of China(Grant No.20101333110002)
文摘Durning the design process of hydrostatic rotary worktable,the processing and assembly tolerance,（the offset of worktable and the gap of the oil film’s thickness）is ignored.But it will cause that the real bearing of oil pocket deviates from the initial design value,and then the performance of rotary worktable will be reduced significantly.Up to now,no effort is found toward the research of influence of the processing and assembly tolerance on the performance of the rotary worktable.So the hydrostatic oil film is assumed as the elastomer in this paper,and then the bearing capacity of the oil pocket is studied with and without the mass offset of the worktable by taking an expression between the bearing capacity and the oil film’s thickness of the oil pocket as the deform compatibility equation.The influence of the processing tolerance of the oil sealing belt’s gap on the bearing capacity of the oil pocket is analyzed.In the light of the liquid hydrostatic worktable of Gantry Moving Milling Center using on the scene,the oil pocket’s pressure of the worktable is tested using Rotary Worktable Test System under the circumstance of the mass offset of the worktable and the gap tolerance of the oil sealing belt,and then the equivalent offset of worktable,the average pressure of the oil pocket and the actual thickness of the oil film are analyzed respectively.The test results show that the bearing capacity component of the oil pocket caused by G is consistent,and the component caused by M is relative to the position of the oil pocket.When the oil sealing belt’s gap is larger than the theoretical value,the bearing capacity of the oil pocket is smaller than the others;whereas the bearing capacity of the oil pocket is larger than the others.The maximum and minimum equivalent offsets are 0.256 4 mm and 0.047 5 mm,respectively,and the average oil pocket pressure varies from 0.345 MPa to 0.460 MPa,the maximum and minimum value of the actual oil film thickness are 109.976？m（No.7 oil pocket）and 93.467？m（No.10 oil pocket）,respectively.The research results can be used to detect the offset of the worktable and the actual thickness of the oil film under processing and assembly tolerance,and provides a basis way for detecting the processing and assembly tolerance of rotary worktable signing reasonably of Gantry Moving Milling Center.
文摘目的:使用CT联合Mimics软件测量全髋关节置换术(total hip arthroplasty,THA)后股骨偏心距(femoral offset,FO)、旋转中心高度(rotation center height,RCH)与双下肢长度差(lower leg length discrepancy,LLD),并探讨THA后FO、RCH与LLD的关系。方法:回顾性分析2020年10月至2022年6月符合标准的40例行单侧THA的患者,其中男21例,女19例;年龄30~81(58.90±14.13)岁;身体质量指数(body mass index,BMI)为17.3~31.5(25.3±3.4)kg·m^(-2);左侧18例,右侧22例。诊断为股骨头坏死30例(FicatⅣ期),髋关节骨性关节炎2例(TünnisⅢ期),发育性髋关节脱位合并终末期骨关节炎2例(CroweⅢ期),股骨颈骨折6例(GardenⅣ期)。术前、术后拍摄骨盆CT三维重建,经Mimics软件处理后建立三维重建模型,在模型上对FO、RCH、LLD进行测量。结果:术后双侧FO差值与LLD呈正相关性(r=0.744,P<0.001);将FO重建组与偏心距未重建组进行卡方检验得出:FO重建组下肢等长率高于FO未重建组(χ^(2)=6.320,P=0.012)。术后双侧RCH差值与LLD呈负相关性(r=-0.877,P<0.001);双侧FO差值及双侧RCH差值与术后LLD之间存在线性关系,且满足线性回归方程:术后LLD=0.038x-0.099y+0.257(x为术后双侧FO差值;y为术后双侧RCH差值;单位为cm),F=77.993,R2=0.808,P=0.009。结论:THA术后LLD随着FO的增大而增大,随着RCH增大而减小;重建FO更易获得下肢等长效果。THA术后双侧FO差值及双侧RCH差值与LLD之间存在线性关系,回归方程可为判断LLD提供一种理论参考。
