Streak tube imaging lidar （STIL） is an active imaging system that has a high range accuracy with tile use of a pulsed lapser transmitter and streak tube receiver to produce 3D range inlages. This work investigates t...Streak tube imaging lidar （STIL） is an active imaging system that has a high range accuracy with tile use of a pulsed lapser transmitter and streak tube receiver to produce 3D range inlages. This work investigates the effect of tile time bin size oil the range accuracy of STIL systems based on the peak detection algorithm. The nunlerical simulation indicates that the time bin size has a significant effect on the range aceuracy, resulting in a modified analytical estimate of the range error. An indoor experilnent with a planar target is carried out to validate the theory that shows the linear relationship between tile range error and the time bin size. Finer 3D depth iinages of a fist model are acquired by using a smaller time bin size and the best range error of 0.003 In is achieved with the optimal time bin size of 0.07 ns.展开更多
This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduc...This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction （XRD）, respectively. Our results show that the average grain size of samples decreases from about 830 nm to 127 nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.展开更多
Given a list of items and a sequence of variable-sized bins arriving one by one, it is NP-hard to pack the items into the bin list with a goal to minimize the total size of bins from the earliest one to the last used....Given a list of items and a sequence of variable-sized bins arriving one by one, it is NP-hard to pack the items into the bin list with a goal to minimize the total size of bins from the earliest one to the last used. In this paper a set of approximation algorithms is presented for cases in which the ability to preview at most k(>=2) arriving bins is given. With the essential assumption that all bin sizes are not less than the largest item size, analytical results show the asymptotic worst case ratios of all k-bounded space and offline algorithms are 2. Based on experiments by applying algorithms to instances in which item sizes and bin sizes are drawn independently from the continuous uniform distribution respectively in the interval [0,u] and [u,1], average- case experimental results show that, with fixed k, algorithms with the Best Fit packing(closing) rule are statistically better than those with the First Fit packing(closing) rule.展开更多
基金supported by the National Key Scientific Instrument and Equipment Development Projects of China under Grant No.2012YQ040164
文摘Streak tube imaging lidar （STIL） is an active imaging system that has a high range accuracy with tile use of a pulsed lapser transmitter and streak tube receiver to produce 3D range inlages. This work investigates the effect of tile time bin size oil the range accuracy of STIL systems based on the peak detection algorithm. The nunlerical simulation indicates that the time bin size has a significant effect on the range aceuracy, resulting in a modified analytical estimate of the range error. An indoor experilnent with a planar target is carried out to validate the theory that shows the linear relationship between tile range error and the time bin size. Finer 3D depth iinages of a fist model are acquired by using a smaller time bin size and the best range error of 0.003 In is achieved with the optimal time bin size of 0.07 ns.
基金supported by the National Natural Science Foundation of China (Grant No 50572067)
文摘This paper reports a novel method of repetitive uniaxial compression combined with accumulative fold for preparing bulk submicron- to nanocrystalline copper starting with a coarse grained counterpart. Grain size reduction and microstrain variations of the high purity copper samples after different passes of compression and fold are investigated by scanning electron microscope and x-ray diffraction （XRD）, respectively. Our results show that the average grain size of samples decreases from about 830 nm to 127 nm as the number of compression passes increases to 30. Microstrain in the compressed sample is found to increase for the first 20 passes, but to decrease at the last 10 passes. The variations of compressive yield strength and the shift of XRD peaks to larger diffraction angles are observed in the squeezed sample. Our experimental results demonstrate that the repetitive uniaxial compression combined with accumulative fold is an effective method to prepare bulk nanocrystalline metallic materials, in particular for soft metals such as Cu, Al and Pb.
文摘Given a list of items and a sequence of variable-sized bins arriving one by one, it is NP-hard to pack the items into the bin list with a goal to minimize the total size of bins from the earliest one to the last used. In this paper a set of approximation algorithms is presented for cases in which the ability to preview at most k(>=2) arriving bins is given. With the essential assumption that all bin sizes are not less than the largest item size, analytical results show the asymptotic worst case ratios of all k-bounded space and offline algorithms are 2. Based on experiments by applying algorithms to instances in which item sizes and bin sizes are drawn independently from the continuous uniform distribution respectively in the interval [0,u] and [u,1], average- case experimental results show that, with fixed k, algorithms with the Best Fit packing(closing) rule are statistically better than those with the First Fit packing(closing) rule.
