As the 16th BeiDou navigation satellite was successfully launched into space at 23:33 Beijing Time from the Xichang Satellite Launch Center (XSLC) on October 25, 2012, China completed the construction of the BeiDou Re...As the 16th BeiDou navigation satellite was successfully launched into space at 23:33 Beijing Time from the Xichang Satellite Launch Center (XSLC) on October 25, 2012, China completed the construction of the BeiDou Regional Navigation Satellite System that starts to officially provide services for most parts of the Asia-Pacific region from December 27. The 16th BeiDou navigation satellite, the last one for the regional BeiDou system, was developed by China Academy of Space Technology under CASC.展开更多
Objective:To study the position and the grade of screw perforation in the apical region of adolescent idiopathic scoliosis(AIS)surgery using a calibration technique for the intraoperative navigation error,and to analy...Objective:To study the position and the grade of screw perforation in the apical region of adolescent idiopathic scoliosis(AIS)surgery using a calibration technique for the intraoperative navigation error,and to analyze the related factors of navigation deviation and the clinical significance of the calibration technique.Methods:From 2017 to 2020,a total of 60 Lenke 1 AIS surgical cases were enrolled in this research.The 30 cases received surgery using the intraoperative navigation system(Navigation group)and another 30 cases were assisted with intraoperative navigation system with calibration technique(Calibration group)for the intraoperative navigation error.The basic information and radiological data of the both groups were all recorded.According to the Fu Chang-feng’s pedicle channel classification system,the pedicle on the apical region of the two groups was classified.And then the accuracy of screw placement of the two groups was evaluated according to the Rao’s classification.Results:A total of 600 screws were placed in the two groups.The 297 and 303 pedicle screws were implanted in the navigation group and the calibration group,respectively.In the apical region of the calibration group,the rates of the grade 0 screw placement in type A,B and C pedicle were 95.7%,86.7%and 68.9%respectively.It was a statistically significant difference from the 73.9%,66.9%and 30.0%in the navigation group respectively(P<0.05).In the calibration group,the rates of the medial cortical perforation in the type A,B,C and D pedicle were 0%,1.6%,1.6%and 0%,respectively.The corresponding rates were 16.3%,16.9%,30.0%and 47.6%in the navigation group,respectively.Moreover,in the concave side of the apical region of the calibration group,the rates of the medial cortical perforation in the type A,B,C and D pedicle were 0%,3.6%,2.6%and 0%,respectively.Compared with the calibration group,the corresponding rates were higher in the navigation group(34.4%,25.9%,37.2%and 60.0%,respectively).No serious complications such as spinal cord or neurovascular injury occurred for the two groups.Conclusion:Compared with the intraoperative navigation system,the calibration technique for the intraoperative navigation error could provide the higher accuracy of pedicle screw placement in the apical region of the major curve,the lower medial cortical perforation rate,the less screws misplacement rate on the concave side and the less complication rate of the severe Lenke 1 AIS patients.展开更多
A new proportional navigation(PN) guidance law,called combined proportional navigation(CPN),is proposed.The guidance law is designed to intercept high-speed targets,which is a common case for ballistic targets.The ran...A new proportional navigation(PN) guidance law,called combined proportional navigation(CPN),is proposed.The guidance law is designed to intercept high-speed targets,which is a common case for ballistic targets.The range of target-to-interceptor speed ratio during target interception is derived when guidance laws are applied in high-speed targets interception,and the effectiveness of negative navigation ratio in the PN-based guidance law is proven analytically in some lemmas.Based on the lemmas,the lateral acceleration command of CPN is defined,and the solution to the appearance of singularity in time-varying navigation ratio is given.The simulation results show that CPN can determine headon engagement(as PN) or tail-chase engagement(as RPN) through initial path angle compared with PN and retro proportional navigation(RPN),and can adjust the value of navigation ratio for head-on engagement or tail-chase engagement.Therefore,the capture region of CPN is larger than that of other guidance laws using PN-based methods.展开更多
The characteristics of present “Beidou” satellite positioning system are analyzed. In order to perfect our country regional satellite positioning system, the idea of “Beidou” geosychronous earth orbit （GEO） sate...The characteristics of present “Beidou” satellite positioning system are analyzed. In order to perfect our country regional satellite positioning system, the idea of “Beidou” geosychronous earth orbit （GEO） satellites combined with some middle earth orbit （MEO） satellites constellation is put forward. The details of general satellite constellation optimized method are described, using this method the multiple positioning constellation design results are gained. And those results belong to two type of sehems, one is 2 GEO plus some MEO satellites and the other is 3 GEO plus some MEO satellites. Through simulation and comparison, among those multiple design results, final optimized regional positioning constellation is given. In order to check the chosen constellation cover performance, the position dilution of preeision（PDOP） is calculated, and with ,satellite constellation simulation software Satlab many coverage performances of the chosen constellation substellar point track, elevation, azimuth and visible satellites number changing situation are also simulated.展开更多
A new guidance law, called biased retro proportional navigation(BRPN), is proposed. The guidance law is designed to intercept high-speed targets with angular constraint, which can be used for ballistic target intercep...A new guidance law, called biased retro proportional navigation(BRPN), is proposed. The guidance law is designed to intercept high-speed targets with angular constraint, which can be used for ballistic target interception. BRPN guidance law is defined, and the exact time-varying bias for a required impact angle is derived. Furthermore, the simulation results(trajectory, variation of navigation ratio, capture region, etc) are compared with those of biased proportional navigation(BPN), proportional navigation and retro-proportional navigation. The results show that,at the cost of a higher intercept time, BRPN demands lower terminal lateral acceleration and has larger capture region compared to BPN.展开更多
In order to make the humanoid robot walk freely in complicated circumstance,the reliable capabilities for obtaining plane information from its surroundings are demanded.A system for extracting planes from data taken b...In order to make the humanoid robot walk freely in complicated circumstance,the reliable capabilities for obtaining plane information from its surroundings are demanded.A system for extracting planes from data taken by stereo vision was presented.After the depth image was obtained,the pixels of each line were scanned and split into straight line segments.The neighbouring relation of line segments was kept in link structure.The groups of three line segments were selected as seed regions.A queue was maintained for storing seed regions,and then the plane region was expanded around the seed region.The process of region growing continued until the queue of seed regions was empty.After trimming,the edges of the planes became smooth.In the end,extracted planes were obtained.In the experiment,two models were used:pipe and stairs.Two planes in pipe model and six planes in stairs model were extracted exactly.The speed and precision of algorithm can satisfy the demands of humanoid robot's navigation.展开更多
终端区航空器的飞行密度和复杂度较高,此管制区域的处理能力是制约航空体系效率的瓶颈,对进场航空器管制效率进行量化研究,有助于提高管制工作处理能力和质量。首先,提出以区域导航(RNAV,regional area navigation)标准仪表进场程序的...终端区航空器的飞行密度和复杂度较高,此管制区域的处理能力是制约航空体系效率的瓶颈,对进场航空器管制效率进行量化研究,有助于提高管制工作处理能力和质量。首先,提出以区域导航(RNAV,regional area navigation)标准仪表进场程序的标称里程为计算基准量化进场管制效率,通过随机搜索聚类算法的结果得到航空器使用的RNAV标准仪表进场程序,选用在北京首都国际机场着陆的航空器为分析对象,计算航空器的进场管制效率,结合航迹讨论不同RNAV标准仪表进场程序下航空器的运行方式及特点。其次,对进场管制效率的影响因素进行分析,并采用灰色关联分析法量化各影响因素的影响程度与权重,结果显示:雷达引导度和航行三要素改变次数对进场管制效率具有显著影响,飞行流量和RNAV标准仪表进场程序的标称里程对进场管制效率的影响相对较小。继而,从影响因素角度出发评估整体进场管制效率,得到更为全面客观的整体进场管制效率。最后,尝试从RNAV进场程序路径以及优良管制行为模式两方面寻求进场管制效率的提升途径和方法。展开更多
文摘As the 16th BeiDou navigation satellite was successfully launched into space at 23:33 Beijing Time from the Xichang Satellite Launch Center (XSLC) on October 25, 2012, China completed the construction of the BeiDou Regional Navigation Satellite System that starts to officially provide services for most parts of the Asia-Pacific region from December 27. The 16th BeiDou navigation satellite, the last one for the regional BeiDou system, was developed by China Academy of Space Technology under CASC.
基金National Natural Science Foundation of China(81902270)Young Talents’Science and Technology Innovation Project of Hainan Association for Science and Technology(QCXM202014)。
文摘Objective:To study the position and the grade of screw perforation in the apical region of adolescent idiopathic scoliosis(AIS)surgery using a calibration technique for the intraoperative navigation error,and to analyze the related factors of navigation deviation and the clinical significance of the calibration technique.Methods:From 2017 to 2020,a total of 60 Lenke 1 AIS surgical cases were enrolled in this research.The 30 cases received surgery using the intraoperative navigation system(Navigation group)and another 30 cases were assisted with intraoperative navigation system with calibration technique(Calibration group)for the intraoperative navigation error.The basic information and radiological data of the both groups were all recorded.According to the Fu Chang-feng’s pedicle channel classification system,the pedicle on the apical region of the two groups was classified.And then the accuracy of screw placement of the two groups was evaluated according to the Rao’s classification.Results:A total of 600 screws were placed in the two groups.The 297 and 303 pedicle screws were implanted in the navigation group and the calibration group,respectively.In the apical region of the calibration group,the rates of the grade 0 screw placement in type A,B and C pedicle were 95.7%,86.7%and 68.9%respectively.It was a statistically significant difference from the 73.9%,66.9%and 30.0%in the navigation group respectively(P<0.05).In the calibration group,the rates of the medial cortical perforation in the type A,B,C and D pedicle were 0%,1.6%,1.6%and 0%,respectively.The corresponding rates were 16.3%,16.9%,30.0%and 47.6%in the navigation group,respectively.Moreover,in the concave side of the apical region of the calibration group,the rates of the medial cortical perforation in the type A,B,C and D pedicle were 0%,3.6%,2.6%and 0%,respectively.Compared with the calibration group,the corresponding rates were higher in the navigation group(34.4%,25.9%,37.2%and 60.0%,respectively).No serious complications such as spinal cord or neurovascular injury occurred for the two groups.Conclusion:Compared with the intraoperative navigation system,the calibration technique for the intraoperative navigation error could provide the higher accuracy of pedicle screw placement in the apical region of the major curve,the lower medial cortical perforation rate,the less screws misplacement rate on the concave side and the less complication rate of the severe Lenke 1 AIS patients.
文摘A new proportional navigation(PN) guidance law,called combined proportional navigation(CPN),is proposed.The guidance law is designed to intercept high-speed targets,which is a common case for ballistic targets.The range of target-to-interceptor speed ratio during target interception is derived when guidance laws are applied in high-speed targets interception,and the effectiveness of negative navigation ratio in the PN-based guidance law is proven analytically in some lemmas.Based on the lemmas,the lateral acceleration command of CPN is defined,and the solution to the appearance of singularity in time-varying navigation ratio is given.The simulation results show that CPN can determine headon engagement(as PN) or tail-chase engagement(as RPN) through initial path angle compared with PN and retro proportional navigation(RPN),and can adjust the value of navigation ratio for head-on engagement or tail-chase engagement.Therefore,the capture region of CPN is larger than that of other guidance laws using PN-based methods.
文摘The characteristics of present “Beidou” satellite positioning system are analyzed. In order to perfect our country regional satellite positioning system, the idea of “Beidou” geosychronous earth orbit （GEO） satellites combined with some middle earth orbit （MEO） satellites constellation is put forward. The details of general satellite constellation optimized method are described, using this method the multiple positioning constellation design results are gained. And those results belong to two type of sehems, one is 2 GEO plus some MEO satellites and the other is 3 GEO plus some MEO satellites. Through simulation and comparison, among those multiple design results, final optimized regional positioning constellation is given. In order to check the chosen constellation cover performance, the position dilution of preeision（PDOP） is calculated, and with ,satellite constellation simulation software Satlab many coverage performances of the chosen constellation substellar point track, elevation, azimuth and visible satellites number changing situation are also simulated.
文摘A new guidance law, called biased retro proportional navigation(BRPN), is proposed. The guidance law is designed to intercept high-speed targets with angular constraint, which can be used for ballistic target interception. BRPN guidance law is defined, and the exact time-varying bias for a required impact angle is derived. Furthermore, the simulation results(trajectory, variation of navigation ratio, capture region, etc) are compared with those of biased proportional navigation(BPN), proportional navigation and retro-proportional navigation. The results show that,at the cost of a higher intercept time, BRPN demands lower terminal lateral acceleration and has larger capture region compared to BPN.
基金Project(60776816) supported by the National Natural Science Foundation of China and Civil Aviation Administration of ChinaProject(8251064101000005) supported by the Natural Science Foundation of Guangdong Province,China
文摘In order to make the humanoid robot walk freely in complicated circumstance,the reliable capabilities for obtaining plane information from its surroundings are demanded.A system for extracting planes from data taken by stereo vision was presented.After the depth image was obtained,the pixels of each line were scanned and split into straight line segments.The neighbouring relation of line segments was kept in link structure.The groups of three line segments were selected as seed regions.A queue was maintained for storing seed regions,and then the plane region was expanded around the seed region.The process of region growing continued until the queue of seed regions was empty.After trimming,the edges of the planes became smooth.In the end,extracted planes were obtained.In the experiment,two models were used:pipe and stairs.Two planes in pipe model and six planes in stairs model were extracted exactly.The speed and precision of algorithm can satisfy the demands of humanoid robot's navigation.
文摘终端区航空器的飞行密度和复杂度较高,此管制区域的处理能力是制约航空体系效率的瓶颈,对进场航空器管制效率进行量化研究,有助于提高管制工作处理能力和质量。首先,提出以区域导航(RNAV,regional area navigation)标准仪表进场程序的标称里程为计算基准量化进场管制效率,通过随机搜索聚类算法的结果得到航空器使用的RNAV标准仪表进场程序,选用在北京首都国际机场着陆的航空器为分析对象,计算航空器的进场管制效率,结合航迹讨论不同RNAV标准仪表进场程序下航空器的运行方式及特点。其次,对进场管制效率的影响因素进行分析,并采用灰色关联分析法量化各影响因素的影响程度与权重,结果显示:雷达引导度和航行三要素改变次数对进场管制效率具有显著影响,飞行流量和RNAV标准仪表进场程序的标称里程对进场管制效率的影响相对较小。继而,从影响因素角度出发评估整体进场管制效率,得到更为全面客观的整体进场管制效率。最后,尝试从RNAV进场程序路径以及优良管制行为模式两方面寻求进场管制效率的提升途径和方法。
