In the traditional views on developmental biology, the process of a mammal from a zygote to. an adult individual follows continuous changes of space and time environments and is the result of different expressions of ...In the traditional views on developmental biology, the process of a mammal from a zygote to. an adult individual follows continuous changes of space and time environments and is the result of different expressions of target genes. It has long been known that this process is irreversible and the terminal differentiated adult cells, such as cardiac myocytes and neurons, will not divide and differentiate. But recent reports on the two hottest fields - cloning medicine and stem cell biology doubted these concepts. This may lead to a further understanding of the potentiality of mammal development and may provide great chances for commercial and clinical practice.展开更多
This study explores the potential of assimilating data from multiple instruments onboard high-altitude,longendurance unmanned aircraft to improve hurricane analyses and forecasts.A recent study found a signifi cant po...This study explores the potential of assimilating data from multiple instruments onboard high-altitude,longendurance unmanned aircraft to improve hurricane analyses and forecasts.A recent study found a signifi cant positive impact on analyses and forecasts of Hurricane Karl when an ensemble Kalman fi lter was used to assimilate data from the High-altitude Imaging Wind and Rain Airborne Profi ler(HIWRAP),a new Doppler radar onboard the NASA Global Hawk(GH)unmanned airborne system.The GH can also carry other useful instruments,including dropsondes and the Hurricane Imaging Radiometer(HIRAD),which is a new radiometer that estimates large swaths of wind speeds and rainfall at the ocean surface.The primary fi nding is that simultaneously assimilating data from HIWRAP and the other GH-compatible instruments results in further analysis and forecast improvement for Karl.The greatest improvement comes when HIWRAP,HIRAD,and dropsonde data are simultaneously assimilated.展开更多
为了解决快速搜索随机树(Rapid-exploration Random Tree,RRT)算法在机器人路径规划中效率低、复杂度高、趋向性差等问题,提出了一种目标偏向性的改进RRT算法。首先,建立复杂的多障碍物环境模型,并利用KD-Tree算法将待规划空间进行多级...为了解决快速搜索随机树(Rapid-exploration Random Tree,RRT)算法在机器人路径规划中效率低、复杂度高、趋向性差等问题,提出了一种目标偏向性的改进RRT算法。首先,建立复杂的多障碍物环境模型,并利用KD-Tree算法将待规划空间进行多级分割;其次,在RRT算法的基础上引入变权重的人工势场法,算法的主要作用是实现避开障碍物和启发式搜索;最后,实现对RRT算法的改进。通过对改进的RRT算法进行仿真验证,结果表明:该算法缩短了路径规划的时间,减少采样点数目,使生成的路径更加平滑,更适用于机器人在多障碍物环境中的路径规划。展开更多
针对传统RRT^(*)算法(Rapidly-Exploring Random Tree,RRT)在全局路径规划过程中存在收敛速度慢、搜索路径不平滑、内存占用多等问题,提出了一种APF-RRT^(*)(Artificial Potential Field,APF)融合搜索算法。首先,为了加快RRT^(*)算法在...针对传统RRT^(*)算法(Rapidly-Exploring Random Tree,RRT)在全局路径规划过程中存在收敛速度慢、搜索路径不平滑、内存占用多等问题,提出了一种APF-RRT^(*)(Artificial Potential Field,APF)融合搜索算法。首先,为了加快RRT^(*)算法在搜寻过程中的收敛速度,在算法中利用人工势场引导快速扩展随机树向目标点生长,在RRT^(*)算法扩展节点时加入APF的目标引力与障碍物斥力思想;其次,对融合算法在空间中的采样范围做出改进,使算法在APF产生的合力特定范围内进行采样,提高算法在空间中的搜索效率,减少无用节点的扩展;最后,对融合算法规划的路径进行平滑优化,减少不必要的路径,降低无人机实际飞行的代价。在多种不同障碍物环境下进行了对比仿真实验,融合算法相较于传统RRT和RRT^(*)算法搜索效率显著提升,路径代价与平滑度得到进一步优化,且降低了随机树无用节点的扩展,节点的利用率得到大幅提升。展开更多
基金This work was supported by the "973" Project (Grant No. G1999054205).
文摘In the traditional views on developmental biology, the process of a mammal from a zygote to. an adult individual follows continuous changes of space and time environments and is the result of different expressions of target genes. It has long been known that this process is irreversible and the terminal differentiated adult cells, such as cardiac myocytes and neurons, will not divide and differentiate. But recent reports on the two hottest fields - cloning medicine and stem cell biology doubted these concepts. This may lead to a further understanding of the potentiality of mammal development and may provide great chances for commercial and clinical practice.
基金Funding for this work came the Hurricane and Severe Storm Sentinel Investigation under NASA’s Earth Venture Programfrom the NASA New Investigator Program
文摘This study explores the potential of assimilating data from multiple instruments onboard high-altitude,longendurance unmanned aircraft to improve hurricane analyses and forecasts.A recent study found a signifi cant positive impact on analyses and forecasts of Hurricane Karl when an ensemble Kalman fi lter was used to assimilate data from the High-altitude Imaging Wind and Rain Airborne Profi ler(HIWRAP),a new Doppler radar onboard the NASA Global Hawk(GH)unmanned airborne system.The GH can also carry other useful instruments,including dropsondes and the Hurricane Imaging Radiometer(HIRAD),which is a new radiometer that estimates large swaths of wind speeds and rainfall at the ocean surface.The primary fi nding is that simultaneously assimilating data from HIWRAP and the other GH-compatible instruments results in further analysis and forecast improvement for Karl.The greatest improvement comes when HIWRAP,HIRAD,and dropsonde data are simultaneously assimilated.
文摘为了解决快速搜索随机树(Rapid-exploration Random Tree,RRT)算法在机器人路径规划中效率低、复杂度高、趋向性差等问题,提出了一种目标偏向性的改进RRT算法。首先,建立复杂的多障碍物环境模型,并利用KD-Tree算法将待规划空间进行多级分割;其次,在RRT算法的基础上引入变权重的人工势场法,算法的主要作用是实现避开障碍物和启发式搜索;最后,实现对RRT算法的改进。通过对改进的RRT算法进行仿真验证,结果表明:该算法缩短了路径规划的时间,减少采样点数目,使生成的路径更加平滑,更适用于机器人在多障碍物环境中的路径规划。
文摘针对传统RRT^(*)算法(Rapidly-Exploring Random Tree,RRT)在全局路径规划过程中存在收敛速度慢、搜索路径不平滑、内存占用多等问题,提出了一种APF-RRT^(*)(Artificial Potential Field,APF)融合搜索算法。首先,为了加快RRT^(*)算法在搜寻过程中的收敛速度,在算法中利用人工势场引导快速扩展随机树向目标点生长,在RRT^(*)算法扩展节点时加入APF的目标引力与障碍物斥力思想;其次,对融合算法在空间中的采样范围做出改进,使算法在APF产生的合力特定范围内进行采样,提高算法在空间中的搜索效率,减少无用节点的扩展;最后,对融合算法规划的路径进行平滑优化,减少不必要的路径,降低无人机实际飞行的代价。在多种不同障碍物环境下进行了对比仿真实验,融合算法相较于传统RRT和RRT^(*)算法搜索效率显著提升,路径代价与平滑度得到进一步优化,且降低了随机树无用节点的扩展,节点的利用率得到大幅提升。
