For spacecraft formation flight,the information of relative motion reachable set is very important,which can be used to predict the operating boundary of adjacent spacecraft and thus to ensure the safety of spacecraft...For spacecraft formation flight,the information of relative motion reachable set is very important,which can be used to predict the operating boundary of adjacent spacecraft and thus to ensure the safety of spacecraft operation.In this paper,we aim at developing a numerical method to approximate the reachable set for spacecraft relative motion.In particular,we focus on the quality of the approximation and the computational cost.Based on the bang-bang control principle,a polyhedral approximation algorithm is proposed to compute the reachable set of a relative motion spacecraft system.An inner approximation and an outer approximation of the reachable set for the system can be obtained.We prove that the approximation quality measured in Hausdorff distance can be guaranteed.The method is easy to implement and has low computational cost.Finally,the effectiveness of the algorithm is demonstrated by experimental simulation.展开更多
揭示三江源国家公园典型高寒草地的冷季牧草营养特征和食草动物承载力,对园区内草地与食草动物平衡管理具有重要意义,然而相关地面研究鲜有报道.本研究于2019年12月对三江源国家公园长江源园区的紫花针茅草原、藏嵩草草甸和青藏苔草草...揭示三江源国家公园典型高寒草地的冷季牧草营养特征和食草动物承载力,对园区内草地与食草动物平衡管理具有重要意义,然而相关地面研究鲜有报道.本研究于2019年12月对三江源国家公园长江源园区的紫花针茅草原、藏嵩草草甸和青藏苔草草原进行调查取样,分析了该地区冷季牧草地上现存量和营养品质,同时结合农业行业标准(NY/T635-2015)核算了冷季数量承载力、可消化蛋白承载力和代谢能承载力.结果表明:(1)冷季牧草干物质现存量表现为藏嵩草草甸(103.03 g DM/m^2)>紫花针茅草原(72.24 g DM/m^2)>青藏苔草草原(21.08 g DM/m^2)(P<0.01);(2)冷季牧草粗蛋白含量表现为藏嵩草草甸(5.16%)极显著高于紫花针茅草原(3.95%)和青藏苔草草原(4.32%)(P<0.01);(3)冷季牧草干物质、粗蛋白和代谢能的单位草地面积输出总量均表现为藏嵩草草甸>紫花针茅草原>青藏苔草草原(P<0.01);(4)三类典型草地冷季承载力均表现为代谢能承载力>数量承载力>可消化蛋白承载力,表明代谢能承载力可以满足食草动物需求,采用可消化蛋白承载力有助于缓解国家公园内天然草地放牧压力,更符合生态保护的目标.紫花针茅草原、藏嵩草草甸和青藏苔草草原冷季的可消化蛋白承载力分别为0.84±0.04、1.57±0.07和0.27±0.02 SHU/ha(标准羊单位/公顷),对应草地代表性食草动物承载力分别为0.17±0.01家牦牛/ha、0.39±0.02藏野驴/ha和0.22±0.02藏羚羊/ha;(5)三江源国家公园高寒草地冷季食草动物承载力整体偏低,建议在国家公园内牧业生产区,通过转变畜牧业经营方式(如放牧家畜暖季末期适时出栏、冷季异地舍饲出栏等)加快家畜周转速率,减少国家公园内放牧家畜存栏数量,为野生动物保护释放草地资源和生态空间.展开更多
Radiotherapy remains the mainstay for treatment of various types of human cancer;however,the clinical efficacy is often limited by radioresistance,in which the underlying mechanism is largely unknown.Here,using esopha...Radiotherapy remains the mainstay for treatment of various types of human cancer;however,the clinical efficacy is often limited by radioresistance,in which the underlying mechanism is largely unknown.Here,using esophageal squamous cell carcinoma(ESCC)as a model,we demonstrate that guanine nucleotide exchange factor 2(VAV2),which is overexpressed in most human cancers,plays an important role in primary and secondary radioresistance.We have discovered for the first time that VAV2 is required for the Ku70/Ku80 complex formation and participates in non-homologous end joining repair of DNA damages caused by ionizing radiation.展开更多
基金partially supported by the National Natural Science Foundation of China(No.12071025)the Natural Science Foundation of Guangdong Province,China(No.2022A1515011172)+1 种基金the Science and Technology on Space Intelligent Control Laboratory for National Defense,China(No.KGJZDSYS-2018-13)the Scientific and Technological Innovation of Shunde Graduate School of University of Science and Technology Beijing,China(No.BK20AE004)。
文摘For spacecraft formation flight,the information of relative motion reachable set is very important,which can be used to predict the operating boundary of adjacent spacecraft and thus to ensure the safety of spacecraft operation.In this paper,we aim at developing a numerical method to approximate the reachable set for spacecraft relative motion.In particular,we focus on the quality of the approximation and the computational cost.Based on the bang-bang control principle,a polyhedral approximation algorithm is proposed to compute the reachable set of a relative motion spacecraft system.An inner approximation and an outer approximation of the reachable set for the system can be obtained.We prove that the approximation quality measured in Hausdorff distance can be guaranteed.The method is easy to implement and has low computational cost.Finally,the effectiveness of the algorithm is demonstrated by experimental simulation.
文摘揭示三江源国家公园典型高寒草地的冷季牧草营养特征和食草动物承载力,对园区内草地与食草动物平衡管理具有重要意义,然而相关地面研究鲜有报道.本研究于2019年12月对三江源国家公园长江源园区的紫花针茅草原、藏嵩草草甸和青藏苔草草原进行调查取样,分析了该地区冷季牧草地上现存量和营养品质,同时结合农业行业标准(NY/T635-2015)核算了冷季数量承载力、可消化蛋白承载力和代谢能承载力.结果表明:(1)冷季牧草干物质现存量表现为藏嵩草草甸(103.03 g DM/m^2)>紫花针茅草原(72.24 g DM/m^2)>青藏苔草草原(21.08 g DM/m^2)(P<0.01);(2)冷季牧草粗蛋白含量表现为藏嵩草草甸(5.16%)极显著高于紫花针茅草原(3.95%)和青藏苔草草原(4.32%)(P<0.01);(3)冷季牧草干物质、粗蛋白和代谢能的单位草地面积输出总量均表现为藏嵩草草甸>紫花针茅草原>青藏苔草草原(P<0.01);(4)三类典型草地冷季承载力均表现为代谢能承载力>数量承载力>可消化蛋白承载力,表明代谢能承载力可以满足食草动物需求,采用可消化蛋白承载力有助于缓解国家公园内天然草地放牧压力,更符合生态保护的目标.紫花针茅草原、藏嵩草草甸和青藏苔草草原冷季的可消化蛋白承载力分别为0.84±0.04、1.57±0.07和0.27±0.02 SHU/ha(标准羊单位/公顷),对应草地代表性食草动物承载力分别为0.17±0.01家牦牛/ha、0.39±0.02藏野驴/ha和0.22±0.02藏羚羊/ha;(5)三江源国家公园高寒草地冷季食草动物承载力整体偏低,建议在国家公园内牧业生产区,通过转变畜牧业经营方式(如放牧家畜暖季末期适时出栏、冷季异地舍饲出栏等)加快家畜周转速率,减少国家公园内放牧家畜存栏数量,为野生动物保护释放草地资源和生态空间.
基金This project was supported by National Science Fund for Distinguished Young Scholars(81725015 to C.W.)Medical and Health Technology Innovation Project of Chinese Academy of Medical Sciences(2016-I2M-3-019 to D.L.,2016-I2M-4-002 to C.W.,2019-I2M-2-001 to D.L.and C.W.,2016-I2M-1-001 and 2019-12M-1-003 to W.T.)+1 种基金Beijing Outstanding Young Scientist Program(BJJWZYJH01201910023027 to C.W.)National Natural Science Foundation of China(81988101 to D.L and C.W.).
文摘Radiotherapy remains the mainstay for treatment of various types of human cancer;however,the clinical efficacy is often limited by radioresistance,in which the underlying mechanism is largely unknown.Here,using esophageal squamous cell carcinoma(ESCC)as a model,we demonstrate that guanine nucleotide exchange factor 2(VAV2),which is overexpressed in most human cancers,plays an important role in primary and secondary radioresistance.We have discovered for the first time that VAV2 is required for the Ku70/Ku80 complex formation and participates in non-homologous end joining repair of DNA damages caused by ionizing radiation.
