In this paper, we consider the local time and the self-intersection local time for a bifractional Brownian motion, and the collision local time for two independent bifractional Brownian motions. We mainly prove the ex...In this paper, we consider the local time and the self-intersection local time for a bifractional Brownian motion, and the collision local time for two independent bifractional Brownian motions. We mainly prove the existence and smoothness of the self-intersection local time and the collision local time, through the strong local nondeterminism of bifractional Brownian motion, L2 convergence and Chaos expansion.展开更多
In this paper, the existence and smoothness of the collision local time are proved for two independent fractional Brownian motions, through L^2 convergence and Chaos expansion. Furthermore, the regularity of the colli...In this paper, the existence and smoothness of the collision local time are proved for two independent fractional Brownian motions, through L^2 convergence and Chaos expansion. Furthermore, the regularity of the collision local time process is studied.展开更多
A linear response history analysis method is used to determine the influence of three factors:geometric incoherency,wave-passage,and local site characteristics on the response of lnulti-support structures subjected to...A linear response history analysis method is used to determine the influence of three factors:geometric incoherency,wave-passage,and local site characteristics on the response of lnulti-support structures subjected to differential ground motions.A one-span frame and a reduced model of a 24-span bridge,located in Las Vegas,Nevada are studied,in which the influence of each of the three factors and their combinations are analyzed.It is revealed that the incoherency of earthquake ground motion can have a dramatic influence on structural response by modifying the dynamics response to uniform excitation and inducing pseudo-static response,which does not exist in structures subjected to uniform excitation.The total response when all three sources of ground motion incoherency are included is generally larger than that of uniform excitation.展开更多
针对微型飞行器(Micro air vehicle,MAV)在室内飞行过程中无法获得GPS信号,而微型惯性单元(Inertial measurement unit,IMU)的陀螺仪和加速度计随机漂移误差较大,提出一种利用单目视觉估计微型飞行器位姿并构建室内环境的方法。在机载...针对微型飞行器(Micro air vehicle,MAV)在室内飞行过程中无法获得GPS信号,而微型惯性单元(Inertial measurement unit,IMU)的陀螺仪和加速度计随机漂移误差较大,提出一种利用单目视觉估计微型飞行器位姿并构建室内环境的方法。在机载单目摄像机拍摄的序列图像中引入一种基于生物视觉的方法获得匹配特征点,并由五点算法获得帧间摄像机运动参数和特征点位置参数的初始解;利用平面关系将特征点的位置信息由三维降低到二维,给出一种局部优化方法求解摄像机运动参数和特征点位置参数的最大似然估计,提高位姿估计和环境构建的精度。最后通过扩展卡尔曼滤波方法融合IMU传感器和单目视觉测量信息解算出微型飞行器的位姿。实验结果表明,该方法能够实时可靠地估计微型飞行器的位置和姿态,构建的环境信息满足导航需求,适用于微型飞行器室内环境中的导航控制。展开更多
After analyzing the characteristics of airborne SAR motion deviation in detail, a new realization method for airborne SAR motion compensation based on two-dimensional division processing is described. By combining the...After analyzing the characteristics of airborne SAR motion deviation in detail, a new realization method for airborne SAR motion compensation based on two-dimensional division processing is described. By combining the division of local tracks in azimuth direction and the division of sub-mapping strips in range direction, the motion deviation will be compensated accurately. Furthermore, both theoretic analysis and simulation result show that by using this method the problems of motion compensation under complex condition with large motion deviation and large mapping strip width can be resolved well.展开更多
In this paper,the local potential of nondivergent flow on beta plane is derived from the motion equa- tion.The conservation principle for vorticity is obtained when the local potential tends to be minimum with the var...In this paper,the local potential of nondivergent flow on beta plane is derived from the motion equa- tion.The conservation principle for vorticity is obtained when the local potential tends to be minimum with the variational technique.Some other properties st,ch as Lagrangian of vorticity equation,energy etc.are also discussed briefly in the paper.展开更多
There are many challenges for robot navigation in densely populated dynamic environments.This paper presents a survey of the path planning methods for robot navigation in dense environments.Particularly,the path plann...There are many challenges for robot navigation in densely populated dynamic environments.This paper presents a survey of the path planning methods for robot navigation in dense environments.Particularly,the path planning in the navigation framework of mobile robots is composed of global path planning and local path planning,with regard to the planning scope and the executability.Within this framework,the recent progress of the path planning methods is presented in the paper,while examining their strengths and weaknesses.Notably,the recent developed Velocity Obstacle method and its variants that serve as the local planner are analyzed comprehensively.Moreover,as a model-free method that is widely used in current robot applications,the reinforcement learning-based path planning algorithms are detailed in this paper.展开更多
We propose a motion planning gap-based algorithms for mobile robots in an unknown environment for exploration purposes. The results are locally optimal and sufficient to navigate and explore the environment. In contra...We propose a motion planning gap-based algorithms for mobile robots in an unknown environment for exploration purposes. The results are locally optimal and sufficient to navigate and explore the environment. In contrast with the traditional roadmap-based algorithms, our proposed algorithm is designed to use minimal sensory data instead of costly ones. Therefore, we adopt a dynamic data structure called Gap Navigation Trees (GNT), which keeps track of the depth discontinuities (gaps) of the local environment. It is incrementally constructed as the robot which navigates the environment. Upon exploring the whole environment, the resulting final data structure exemplifies the roadmap required for further processing. To avoid infinite cycles, we propose to use landmarks. Similar to traditional roadmap techniques, the resulting algorithm can serve key applications such as exploration and target finding. The simulation results endorse this conclusion. However, our solution is cost effective, when compared to traditional roadmap systems, which makes it more attractive to use in some applications such as search and rescue in hazardous environments.展开更多
基金supported by National Natural Science Foundation of China (Grant No.10871103)
文摘In this paper, we consider the local time and the self-intersection local time for a bifractional Brownian motion, and the collision local time for two independent bifractional Brownian motions. We mainly prove the existence and smoothness of the self-intersection local time and the collision local time, through the strong local nondeterminism of bifractional Brownian motion, L2 convergence and Chaos expansion.
基金the National Natural Science Foundation of China(No. 10471003).
文摘In this paper, the existence and smoothness of the collision local time are proved for two independent fractional Brownian motions, through L^2 convergence and Chaos expansion. Furthermore, the regularity of the collision local time process is studied.
基金the China Scholarship Council and the Teaching and Research Award Program for Outstanding Young Teachers (TRAPOYT) in Higher Education Institutions of MOE,PRC.
文摘A linear response history analysis method is used to determine the influence of three factors:geometric incoherency,wave-passage,and local site characteristics on the response of lnulti-support structures subjected to differential ground motions.A one-span frame and a reduced model of a 24-span bridge,located in Las Vegas,Nevada are studied,in which the influence of each of the three factors and their combinations are analyzed.It is revealed that the incoherency of earthquake ground motion can have a dramatic influence on structural response by modifying the dynamics response to uniform excitation and inducing pseudo-static response,which does not exist in structures subjected to uniform excitation.The total response when all three sources of ground motion incoherency are included is generally larger than that of uniform excitation.
文摘针对微型飞行器(Micro air vehicle,MAV)在室内飞行过程中无法获得GPS信号,而微型惯性单元(Inertial measurement unit,IMU)的陀螺仪和加速度计随机漂移误差较大,提出一种利用单目视觉估计微型飞行器位姿并构建室内环境的方法。在机载单目摄像机拍摄的序列图像中引入一种基于生物视觉的方法获得匹配特征点,并由五点算法获得帧间摄像机运动参数和特征点位置参数的初始解;利用平面关系将特征点的位置信息由三维降低到二维,给出一种局部优化方法求解摄像机运动参数和特征点位置参数的最大似然估计,提高位姿估计和环境构建的精度。最后通过扩展卡尔曼滤波方法融合IMU传感器和单目视觉测量信息解算出微型飞行器的位姿。实验结果表明,该方法能够实时可靠地估计微型飞行器的位置和姿态,构建的环境信息满足导航需求,适用于微型飞行器室内环境中的导航控制。
文摘After analyzing the characteristics of airborne SAR motion deviation in detail, a new realization method for airborne SAR motion compensation based on two-dimensional division processing is described. By combining the division of local tracks in azimuth direction and the division of sub-mapping strips in range direction, the motion deviation will be compensated accurately. Furthermore, both theoretic analysis and simulation result show that by using this method the problems of motion compensation under complex condition with large motion deviation and large mapping strip width can be resolved well.
文摘In this paper,the local potential of nondivergent flow on beta plane is derived from the motion equa- tion.The conservation principle for vorticity is obtained when the local potential tends to be minimum with the variational technique.Some other properties st,ch as Lagrangian of vorticity equation,energy etc.are also discussed briefly in the paper.
文摘There are many challenges for robot navigation in densely populated dynamic environments.This paper presents a survey of the path planning methods for robot navigation in dense environments.Particularly,the path planning in the navigation framework of mobile robots is composed of global path planning and local path planning,with regard to the planning scope and the executability.Within this framework,the recent progress of the path planning methods is presented in the paper,while examining their strengths and weaknesses.Notably,the recent developed Velocity Obstacle method and its variants that serve as the local planner are analyzed comprehensively.Moreover,as a model-free method that is widely used in current robot applications,the reinforcement learning-based path planning algorithms are detailed in this paper.
文摘We propose a motion planning gap-based algorithms for mobile robots in an unknown environment for exploration purposes. The results are locally optimal and sufficient to navigate and explore the environment. In contrast with the traditional roadmap-based algorithms, our proposed algorithm is designed to use minimal sensory data instead of costly ones. Therefore, we adopt a dynamic data structure called Gap Navigation Trees (GNT), which keeps track of the depth discontinuities (gaps) of the local environment. It is incrementally constructed as the robot which navigates the environment. Upon exploring the whole environment, the resulting final data structure exemplifies the roadmap required for further processing. To avoid infinite cycles, we propose to use landmarks. Similar to traditional roadmap techniques, the resulting algorithm can serve key applications such as exploration and target finding. The simulation results endorse this conclusion. However, our solution is cost effective, when compared to traditional roadmap systems, which makes it more attractive to use in some applications such as search and rescue in hazardous environments.
