针对小型合成孔径雷达(synthetic aperture radar,SAR)平台曲线轨迹运动、大斜视实时成像的要求,提出一种子孔径成像算法,首先进行预处理,补偿加速度对调频率的影响,再采用级数反演法(method of series reversion,MSR)得到回波信号的高...针对小型合成孔径雷达(synthetic aperture radar,SAR)平台曲线轨迹运动、大斜视实时成像的要求,提出一种子孔径成像算法,首先进行预处理,补偿加速度对调频率的影响,再采用级数反演法(method of series reversion,MSR)得到回波信号的高阶近似二维谱。在此基础上,基于方位频域相位滤波处理校正方位调频率空变,最终利用谱分析(spectrum analysis,SPECAN)技术实现方位统一聚焦。点目标仿真数据验证了本文算法的有效性。展开更多
Using molecular dynamics simulations,we show that an asymmetrically shaped nanoparticle in dilute solution possesses a spontaneously curved trajectory within a finite time interval,instead of the generally expected ra...Using molecular dynamics simulations,we show that an asymmetrically shaped nanoparticle in dilute solution possesses a spontaneously curved trajectory within a finite time interval,instead of the generally expected random walk.This unexpected dynamic behavior has a similarity to that of active matters,such as swimming bacteria,cells,or even fish,but is of a different physical origin.The key to the curved trajectory lies in the non-zero resultant force originated from the imbalance of the collision forces acted by surrounding solvent molecules on the asymmetrically shaped nanoparticle during its orientation regulation.Theoretical formulae based on microscopic observations have been derived to describe this non-zero force and the resulting motion of the asymmetrically shaped nanoparticle.展开更多
文摘为了研究车辆在单曲线上行驶时的运动学行为和驾驶行为,在ADAMS软件环境下创建了小客车的动力学模型,进行了切弯和跟弯两种驾驶模式的单曲线行驶试验.根据仿真输出的转向盘角度变化,将转向过程划分为进弯、维持和出弯3个阶段,分别得到了车辆进弯和出弯时的转向长度和转向时间,以及这2个参量与弯道半径、转角和车辆轴距的关系.研究结果表明:当弯道转角不超过某个临界值时,转向盘转角、转向时间以及转向长度随着弯道转角的增大而增大,并且切弯时更显著;当弯道半径不超过550 m时,转向长度随弯道半径增大而增大;不同驾驶模式会导致转向长度出现显著差别,切弯时的稳定转向长度约为跟弯时的2倍;切弯模式的"稳定转向时间-弯道半径"曲线先升后降,呈抛物线形状,而采用跟弯模式时该曲线呈单调下降趋势,2种模式的平均转向时间为3.75 s.
文摘针对小型合成孔径雷达(synthetic aperture radar,SAR)平台曲线轨迹运动、大斜视实时成像的要求,提出一种子孔径成像算法,首先进行预处理,补偿加速度对调频率的影响,再采用级数反演法(method of series reversion,MSR)得到回波信号的高阶近似二维谱。在此基础上,基于方位频域相位滤波处理校正方位调频率空变,最终利用谱分析(spectrum analysis,SPECAN)技术实现方位统一聚焦。点目标仿真数据验证了本文算法的有效性。
基金supported by the National Natural Science Foundation of China(Grant Nos.10825520,11422542,11175230,and 11290164)the Key Research Program of the Chinese Academy of Sciences(Grant No.KJZD-EW-M03)Deepcomp7000 and ScGrid of the Supercomputing Center,the Computer Network Information Center of the Chinese Academy of Sciences, and the Shanghai Supercomputer Center of China
文摘Using molecular dynamics simulations,we show that an asymmetrically shaped nanoparticle in dilute solution possesses a spontaneously curved trajectory within a finite time interval,instead of the generally expected random walk.This unexpected dynamic behavior has a similarity to that of active matters,such as swimming bacteria,cells,or even fish,but is of a different physical origin.The key to the curved trajectory lies in the non-zero resultant force originated from the imbalance of the collision forces acted by surrounding solvent molecules on the asymmetrically shaped nanoparticle during its orientation regulation.Theoretical formulae based on microscopic observations have been derived to describe this non-zero force and the resulting motion of the asymmetrically shaped nanoparticle.
