Every year, around the world, between 250,000 and 500,000 people suffer a spinal cord injury(SCI). SCI is a devastating medical condition that arises from trauma or disease-induced damage to the spinal cord, disruptin...Every year, around the world, between 250,000 and 500,000 people suffer a spinal cord injury(SCI). SCI is a devastating medical condition that arises from trauma or disease-induced damage to the spinal cord, disrupting the neural connections that allow communication between the brain and the rest of the body, which results in varying degrees of motor and sensory impairment. Disconnection in the spinal tracts is an irreversible condition owing to the poor capacity for spontaneous axonal regeneration in the affected neurons.展开更多
During the use of robotics in applications such as antiterrorism or combat,a motion-constrained pursuer vehicle,such as a Dubins unmanned surface vehicle(USV),must get close enough(within a prescribed zero or positive...During the use of robotics in applications such as antiterrorism or combat,a motion-constrained pursuer vehicle,such as a Dubins unmanned surface vehicle(USV),must get close enough(within a prescribed zero or positive distance)to a moving target as quickly as possible,resulting in the extended minimum-time intercept problem(EMTIP).Existing research has primarily focused on the zero-distance intercept problem,MTIP,establishing the necessary or sufficient conditions for MTIP optimality,and utilizing analytic algorithms,such as root-finding algorithms,to calculate the optimal solutions.However,these approaches depend heavily on the properties of the analytic algorithm,making them inapplicable when problem settings change,such as in the case of a positive effective range or complicated target motions outside uniform rectilinear motion.In this study,an approach employing a high-accuracy and quality-guaranteed mixed-integer piecewise-linear program(QG-PWL)is proposed for the EMTIP.This program can accommodate different effective interception ranges and complicated target motions(variable velocity or complicated trajectories).The high accuracy and quality guarantees of QG-PWL originate from elegant strategies such as piecewise linearization and other developed operation strategies.The approximate error in the intercept path length is proved to be bounded to h^(2)/(4√2),where h is the piecewise length.展开更多
哨兵(Sentinel)-6A海洋测高卫星搭载了GPS/Galileo双模接收机,为研究基于全球导航卫星系统多星座的低轨卫星精密定轨提供了契机。固定载波相位模糊度可提升低轨卫星的定轨精度,利用在轨实测数据研究GPS/Galileo双系统组合以及模糊度固...哨兵(Sentinel)-6A海洋测高卫星搭载了GPS/Galileo双模接收机,为研究基于全球导航卫星系统多星座的低轨卫星精密定轨提供了契机。固定载波相位模糊度可提升低轨卫星的定轨精度,利用在轨实测数据研究GPS/Galileo双系统组合以及模糊度固定对低轨卫星运动学定轨精度的影响。分别采用欧洲定轨中心(Center for Orbit Determination in Europe,CODE)、法国国家空间研究中心(Centre National d’Etudes Spatiales,CNES)、德国地学研究中心(German Research Centre for Geosciences,GFZ)和中国武汉大学(Wuhan University,WHU)发布的观测值偏差及对应的精密星历和钟差产品开展单接收机模糊度固定。结果表明:GPS/Galileo双系统组合可明显改善定轨几何构型。双系统组合浮点解轨道三维精度优于30 mm,相对于GPS单系统提升超过20%。模糊度固定显著提升了运动学定轨精度,组合固定解轨道精度优于20 mm,相对于GPS提升30%。基于CODE、CNES和GFZ产品的GPS和Galileo单系统模糊度固定率分别优于93%和95%,WHU产品的Galileo固定率则偏低。利用卫星激光测距(satellite laser ranging,SLR)观测数据对运动学定轨结果进行检核,单系统固定解轨道SLR残差均方根误差(root mean square,RMS)为13~15 mm,双系统组合固定解RMS则达到12~14 mm,提升超过10%。展开更多
基金financially supported by Ministerio de Ciencia e Innovación projects SAF2017-82736-C2-1-R to MTMFin Universidad Autónoma de Madrid and by Fundación Universidad Francisco de Vitoria to JS+2 种基金a predoctoral scholarship from Fundación Universidad Francisco de Vitoriafinancial support from a 6-month contract from Universidad Autónoma de Madrida 3-month contract from the School of Medicine of Universidad Francisco de Vitoria。
文摘Every year, around the world, between 250,000 and 500,000 people suffer a spinal cord injury(SCI). SCI is a devastating medical condition that arises from trauma or disease-induced damage to the spinal cord, disrupting the neural connections that allow communication between the brain and the rest of the body, which results in varying degrees of motor and sensory impairment. Disconnection in the spinal tracts is an irreversible condition owing to the poor capacity for spontaneous axonal regeneration in the affected neurons.
基金supported by the National Natural Sci‐ence Foundation of China(Grant No.62306325)。
文摘During the use of robotics in applications such as antiterrorism or combat,a motion-constrained pursuer vehicle,such as a Dubins unmanned surface vehicle(USV),must get close enough(within a prescribed zero or positive distance)to a moving target as quickly as possible,resulting in the extended minimum-time intercept problem(EMTIP).Existing research has primarily focused on the zero-distance intercept problem,MTIP,establishing the necessary or sufficient conditions for MTIP optimality,and utilizing analytic algorithms,such as root-finding algorithms,to calculate the optimal solutions.However,these approaches depend heavily on the properties of the analytic algorithm,making them inapplicable when problem settings change,such as in the case of a positive effective range or complicated target motions outside uniform rectilinear motion.In this study,an approach employing a high-accuracy and quality-guaranteed mixed-integer piecewise-linear program(QG-PWL)is proposed for the EMTIP.This program can accommodate different effective interception ranges and complicated target motions(variable velocity or complicated trajectories).The high accuracy and quality guarantees of QG-PWL originate from elegant strategies such as piecewise linearization and other developed operation strategies.The approximate error in the intercept path length is proved to be bounded to h^(2)/(4√2),where h is the piecewise length.
文摘哨兵(Sentinel)-6A海洋测高卫星搭载了GPS/Galileo双模接收机,为研究基于全球导航卫星系统多星座的低轨卫星精密定轨提供了契机。固定载波相位模糊度可提升低轨卫星的定轨精度,利用在轨实测数据研究GPS/Galileo双系统组合以及模糊度固定对低轨卫星运动学定轨精度的影响。分别采用欧洲定轨中心(Center for Orbit Determination in Europe,CODE)、法国国家空间研究中心(Centre National d’Etudes Spatiales,CNES)、德国地学研究中心(German Research Centre for Geosciences,GFZ)和中国武汉大学(Wuhan University,WHU)发布的观测值偏差及对应的精密星历和钟差产品开展单接收机模糊度固定。结果表明:GPS/Galileo双系统组合可明显改善定轨几何构型。双系统组合浮点解轨道三维精度优于30 mm,相对于GPS单系统提升超过20%。模糊度固定显著提升了运动学定轨精度,组合固定解轨道精度优于20 mm,相对于GPS提升30%。基于CODE、CNES和GFZ产品的GPS和Galileo单系统模糊度固定率分别优于93%和95%,WHU产品的Galileo固定率则偏低。利用卫星激光测距(satellite laser ranging,SLR)观测数据对运动学定轨结果进行检核,单系统固定解轨道SLR残差均方根误差(root mean square,RMS)为13~15 mm,双系统组合固定解RMS则达到12~14 mm,提升超过10%。
