A well-designed reflector surface with high beam pointing accuracy in electromagnetic performance is of practical significance to the space application of cable mesh reflector antennas. As for space requirements, cir-...A well-designed reflector surface with high beam pointing accuracy in electromagnetic performance is of practical significance to the space application of cable mesh reflector antennas. As for space requirements, cir- cular polarizations are widely used in spaceborne antennas, which usually lead to a beam shift for offset reflectors and influence the beam pointing accuracy. A two-step structural design procedure is proposed to overcome the beam squint phenomenon for high beam pointing accuracy design of circularly polarized offset cable mesh reflectors. A simple structural optimal design and an integrated structural electromagnetic optimization are combined to alleviate the beam squint effect of circular polarizations. It is imple- mented by cable pretension design and adjustment to shape the offset cable mesh surface. Besides, in order to increase the efficiency of integrated optimization, an update Broy- den-Fletcher-Goldfarb-Shanno （BFGS） Hessian matrix is employed in the optimization iteration with sequential quadratic programming. A circularly polarized offset cable mesh reflector is utilized to show the feasibility and effectiveness of the proposed procedure. A high beam pointing accuracy in order of 0.0001~ of electromagnetic performance is achieved.展开更多
在图优化框架的基础上,设计多传感器融合方案和有效的优化方法,提出一套具有鲁棒性的定位与建图(Simultaneous Localization and Mapping,SLAM)方案,能够有效应对室内外复杂环境。进一步发展激光-视觉后端建图融合方法,构建具备全新地...在图优化框架的基础上,设计多传感器融合方案和有效的优化方法,提出一套具有鲁棒性的定位与建图(Simultaneous Localization and Mapping,SLAM)方案,能够有效应对室内外复杂环境。进一步发展激光-视觉后端建图融合方法,构建具备全新地图表达形式的点云网格化地图。同时使用低成本传感器,设计实现基于多传感器融合的高性能低成本背包扫描系统,整体完成在未知环境中的自我定位和稠密建图,且在低性能CPU设备上将长时间运动带来的每100 m的轨迹误差平均降低至厘米级。提出的基于多传感器融合方案,在精度、算力消耗上能够匹配现有主流方案,对获取各种环境条件下的系统准确定位结果和丰富的空间信息具有重要意义。展开更多
This paper proposes a new method to simplify mesh in 3D terrain. The 3D terrain is presented by digital elevation model. First, Laplace operator is introduced to calculate sharp degree of mesh point, which indicates t...This paper proposes a new method to simplify mesh in 3D terrain. The 3D terrain is presented by digital elevation model. First, Laplace operator is introduced to calculate sharp degree of mesh point, which indicates the variation trend of the terrain. Through setting a critical value of sharp degree, feature points are selected. Second, critical mesh points are extracted by an recursive process, and constitute the simplified mesh. Third, the algorithm of linear-square interpolation is employed to restore the characteris- tics of the terrain. Last, the terrain is rendered with color and texture. The experimental results demonstrate that this method can compress data by 16% and the error is lower than 10%.展开更多
AIM To retrospectively evaluate the safety and feasibility of a new modified laparoscopic Sugarbaker repair in patients with parastomal hernias.METHODS A retrospective study was performed to analyze eight patients who...AIM To retrospectively evaluate the safety and feasibility of a new modified laparoscopic Sugarbaker repair in patients with parastomal hernias.METHODS A retrospective study was performed to analyze eight patients who underwent parastomal hernia repair between June 2016 and January 2018. All of these patients received modified laparoscopic Sugarbakerhernia repair treatment. This modified technique included an innovative three-point anchoring and complete suturing technique to fix the mesh. All procedures were performed by a skilled hernia surgeon. Demographic data and perioperative outcomes were collected to evaluate the safety and efficacy of this modified technique.RESULTS Of these eight patients, two had concomitant incisional hernias. All the hernias were repaired by the modified laparoscopic Sugarbaker technique with no conversion to laparotomy. Three patients had in-situ reconstruction of intestinal stoma. The median mesh size was300 cm2, and the mean operative time was 205.6 min. The mean postoperative hospitalization time was10.4 d, with a median pain score of 1(visual analog scale method) at postoperative day 1. Two patients developed postoperative complications. One patient had a pocket of effusion surrounding the biologic mesh,and one patient experienced an infection around the reconstructed stoma. Both patients recovered after conservative management. There was no recurrence during the follow-up period(6-22 mo, average 13 mo).CONCLUSION The modified laparoscopic Sugarbaker repair could fix the mesh reliably with mild postoperative pain and a low recurrence rate. The technique is safe and feasible for parastomal hernias.展开更多
Urban vegetation has been an important indicator for the evaluation of eco-cities,which is of great significance to promote eco-city construction. We study and discuss the commonly used urban vegetation extraction met...Urban vegetation has been an important indicator for the evaluation of eco-cities,which is of great significance to promote eco-city construction. We study and discuss the commonly used urban vegetation extraction methods. The extraction of vegetation points in this study is completed through mathematical statistics,mean-square error,successive differences and iterative algorithm which are based on the analysis of different spatial morphological characteristics in urban point clouds. Linyi,a city of Shandong Province in China,is selected as the study area to test this method and the result shows that the proposed method has a strong practicality in urban vegetation point cloud extraction. Only 3D coordinate properties of the LiDAR point clouds are used in this method and it does not require additional information,for instance,return intensity,which makes the method more applicable and operable.展开更多
文摘A well-designed reflector surface with high beam pointing accuracy in electromagnetic performance is of practical significance to the space application of cable mesh reflector antennas. As for space requirements, cir- cular polarizations are widely used in spaceborne antennas, which usually lead to a beam shift for offset reflectors and influence the beam pointing accuracy. A two-step structural design procedure is proposed to overcome the beam squint phenomenon for high beam pointing accuracy design of circularly polarized offset cable mesh reflectors. A simple structural optimal design and an integrated structural electromagnetic optimization are combined to alleviate the beam squint effect of circular polarizations. It is imple- mented by cable pretension design and adjustment to shape the offset cable mesh surface. Besides, in order to increase the efficiency of integrated optimization, an update Broy- den-Fletcher-Goldfarb-Shanno （BFGS） Hessian matrix is employed in the optimization iteration with sequential quadratic programming. A circularly polarized offset cable mesh reflector is utilized to show the feasibility and effectiveness of the proposed procedure. A high beam pointing accuracy in order of 0.0001~ of electromagnetic performance is achieved.
基金The project supported by the Science Foundation of Laboratory of Computational Physics,Science Foundation of China Academy of Engineering Physics,and National Natural Science Foundation of China under Grant Nos.10702010,10775018,10472052,and 10604010
文摘在图优化框架的基础上,设计多传感器融合方案和有效的优化方法,提出一套具有鲁棒性的定位与建图(Simultaneous Localization and Mapping,SLAM)方案,能够有效应对室内外复杂环境。进一步发展激光-视觉后端建图融合方法,构建具备全新地图表达形式的点云网格化地图。同时使用低成本传感器,设计实现基于多传感器融合的高性能低成本背包扫描系统,整体完成在未知环境中的自我定位和稠密建图,且在低性能CPU设备上将长时间运动带来的每100 m的轨迹误差平均降低至厘米级。提出的基于多传感器融合方案,在精度、算力消耗上能够匹配现有主流方案,对获取各种环境条件下的系统准确定位结果和丰富的空间信息具有重要意义。
基金Supported by the National Natural Science Foundation of China (No.61170005)
文摘This paper proposes a new method to simplify mesh in 3D terrain. The 3D terrain is presented by digital elevation model. First, Laplace operator is introduced to calculate sharp degree of mesh point, which indicates the variation trend of the terrain. Through setting a critical value of sharp degree, feature points are selected. Second, critical mesh points are extracted by an recursive process, and constitute the simplified mesh. Third, the algorithm of linear-square interpolation is employed to restore the characteris- tics of the terrain. Last, the terrain is rendered with color and texture. The experimental results demonstrate that this method can compress data by 16% and the error is lower than 10%.
文摘AIM To retrospectively evaluate the safety and feasibility of a new modified laparoscopic Sugarbaker repair in patients with parastomal hernias.METHODS A retrospective study was performed to analyze eight patients who underwent parastomal hernia repair between June 2016 and January 2018. All of these patients received modified laparoscopic Sugarbakerhernia repair treatment. This modified technique included an innovative three-point anchoring and complete suturing technique to fix the mesh. All procedures were performed by a skilled hernia surgeon. Demographic data and perioperative outcomes were collected to evaluate the safety and efficacy of this modified technique.RESULTS Of these eight patients, two had concomitant incisional hernias. All the hernias were repaired by the modified laparoscopic Sugarbaker technique with no conversion to laparotomy. Three patients had in-situ reconstruction of intestinal stoma. The median mesh size was300 cm2, and the mean operative time was 205.6 min. The mean postoperative hospitalization time was10.4 d, with a median pain score of 1(visual analog scale method) at postoperative day 1. Two patients developed postoperative complications. One patient had a pocket of effusion surrounding the biologic mesh,and one patient experienced an infection around the reconstructed stoma. Both patients recovered after conservative management. There was no recurrence during the follow-up period(6-22 mo, average 13 mo).CONCLUSION The modified laparoscopic Sugarbaker repair could fix the mesh reliably with mild postoperative pain and a low recurrence rate. The technique is safe and feasible for parastomal hernias.
文摘Urban vegetation has been an important indicator for the evaluation of eco-cities,which is of great significance to promote eco-city construction. We study and discuss the commonly used urban vegetation extraction methods. The extraction of vegetation points in this study is completed through mathematical statistics,mean-square error,successive differences and iterative algorithm which are based on the analysis of different spatial morphological characteristics in urban point clouds. Linyi,a city of Shandong Province in China,is selected as the study area to test this method and the result shows that the proposed method has a strong practicality in urban vegetation point cloud extraction. Only 3D coordinate properties of the LiDAR point clouds are used in this method and it does not require additional information,for instance,return intensity,which makes the method more applicable and operable.
