Using the frequency-domain theory, we investigate the above-threshold ionization（ATI） process of an atom in twocolor laser fields. When both photon energies of the two-color laser fields are much smaller than the at...Using the frequency-domain theory, we investigate the above-threshold ionization（ATI） process of an atom in twocolor laser fields. When both photon energies of the two-color laser fields are much smaller than the atomic ionization threshold, the ATI spectrum depends on the angle between the two lasers＇ polarization directions. While when the photon energy of one laser is comparable with or larger than the atomic ionization threshold, the ATI spectrum is independent of the angle, and only several dips appear at certain angles. By analyzing the contributions of different quantum channels, we find that, for the case that both frequencies of the two color lasers are low, the quantum interferences between the channels are strong, and hence the spectrum changes with the angle between the two lasers＇ polarization directions. While for the case that the frequency of one of the two color lasers is high, the contributions of the channels to the ATI spectrum decrease dramatically with increasing channel order, hence the interferences between the channels disappear, and the ATI spectrum has a step-like structure, which is independent of the angle between the two lasers＇ polarizations. These results can shed light on the study of the corresponding relation between classical and quantum mechanisms of the matter–laser interaction in high-frequency laser fields.展开更多
According to the frequency-domain theory, we investigate the asymmetric structure of above-threshold ionization(ATI) spectrum of an atom in two-color elliptically polarized(EP) laser fields. When both laser fields are...According to the frequency-domain theory, we investigate the asymmetric structure of above-threshold ionization(ATI) spectrum of an atom in two-color elliptically polarized(EP) laser fields. When both laser fields are linearly polarized(LP), the spectrum shows that the multi-plateau structure is symmetric about the emitted angle of electron at π/2, while the spectrum becomes asymmetric and shifts rightwards with the increase of the EP degree of the IR laser field. Since the total ATI process is regarded as including direct ATI and the rescattering ATI, we analyze the spectrum structure of direct ATI and rescattering ATI separately. Using the saddle-point approximation, we find that for direct ATI, the fringes on the spectrum are mainly attributed to the fact that the ionization probability becomes very small when the direction of emitted electrons is perpendicular to the direction of the XUV laser polarization;while for the rescattering ATI, the interference fringes on the spectrum mainly come from the superposition of the waist structures on the spectra of all sub-channels.展开更多
In this paper, a comprehensive energy function is used to formulate the three most popular objective functions:Kapur's, Otsu and Tsalli's functions for performing effective multilevel color image thresholding....In this paper, a comprehensive energy function is used to formulate the three most popular objective functions:Kapur's, Otsu and Tsalli's functions for performing effective multilevel color image thresholding. These new energy based objective criterions are further combined with the proficient search capability of swarm based algorithms to improve the efficiency and robustness. The proposed multilevel thresholding approach accurately determines the optimal threshold values by using generated energy curve, and acutely distinguishes different objects within the multi-channel complex images. The performance evaluation indices and experiments on different test images illustrate that Kapur's entropy aided with differential evolution and bacterial foraging optimization algorithm generates the most accurate and visually pleasing segmented images.展开更多
In order to make the environment of palmprint recognition more flexible and improve the accuracy of touchless palmprint recognition. This paper proposes a robust, touchless, palmprint recognition system which is based...In order to make the environment of palmprint recognition more flexible and improve the accuracy of touchless palmprint recognition. This paper proposes a robust, touchless, palmprint recognition system which is based on color palmprint images. This system uses skin-color thresholding and hand valley detection algorithm for extracting palmprint. Then, the local binary pattern (LBP) is applied to the palmprint in order to extract the palmprint features. Finally, chi square statistic is used for classification. The experimental results present the equal error rate of 3.7668% and correct recognition rate of 97.0142%. Therefore the results show that this approach is robust and efficient in color palmprint images which are acquired in lighting changes and cluttered background for touch-less palmprint recognition system.展开更多
嵌入式设备中部署深度学习检测模型往往面临算力不足的问题,而感兴趣区域(ROI)提取可作为一种高效的性能优化手段。文章提出一种基于HSV(Hue,Saturation,Value)色彩空间模型的ROI提取的方法,将检测目标的像素信息转化到HSV色彩空间,在色...嵌入式设备中部署深度学习检测模型往往面临算力不足的问题,而感兴趣区域(ROI)提取可作为一种高效的性能优化手段。文章提出一种基于HSV(Hue,Saturation,Value)色彩空间模型的ROI提取的方法,将检测目标的像素信息转化到HSV色彩空间,在色相-饱和度(H-S)平面引入DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法,精确定位目标的主色彩像素在H-S平面上的分布位置,同时过滤杂乱色彩,然后通过Quickhull(快壳)凸包算法,从散点数据中拟合出主色彩的精确分布范围。根据获取的主色彩范围对像素进行遍历,可以根据色彩信息有效地提取ROI。实验结果表明,经过该方法优化后的Faster R-CNN(Faster Regions with Convolutional Neural Networks)算法,较原模型减少了57.08%的平均推理耗时,同时精确率提升了0.9百分点。这对于嵌入式设备中进行实时目标检测具有重要的现实意义。展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11474348 and 61275128)
文摘Using the frequency-domain theory, we investigate the above-threshold ionization（ATI） process of an atom in twocolor laser fields. When both photon energies of the two-color laser fields are much smaller than the atomic ionization threshold, the ATI spectrum depends on the angle between the two lasers＇ polarization directions. While when the photon energy of one laser is comparable with or larger than the atomic ionization threshold, the ATI spectrum is independent of the angle, and only several dips appear at certain angles. By analyzing the contributions of different quantum channels, we find that, for the case that both frequencies of the two color lasers are low, the quantum interferences between the channels are strong, and hence the spectrum changes with the angle between the two lasers＇ polarization directions. While for the case that the frequency of one of the two color lasers is high, the contributions of the channels to the ATI spectrum decrease dramatically with increasing channel order, hence the interferences between the channels disappear, and the ATI spectrum has a step-like structure, which is independent of the angle between the two lasers＇ polarizations. These results can shed light on the study of the corresponding relation between classical and quantum mechanisms of the matter–laser interaction in high-frequency laser fields.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11474348,11674198,11425414,and 11774411)
文摘According to the frequency-domain theory, we investigate the asymmetric structure of above-threshold ionization(ATI) spectrum of an atom in two-color elliptically polarized(EP) laser fields. When both laser fields are linearly polarized(LP), the spectrum shows that the multi-plateau structure is symmetric about the emitted angle of electron at π/2, while the spectrum becomes asymmetric and shifts rightwards with the increase of the EP degree of the IR laser field. Since the total ATI process is regarded as including direct ATI and the rescattering ATI, we analyze the spectrum structure of direct ATI and rescattering ATI separately. Using the saddle-point approximation, we find that for direct ATI, the fringes on the spectrum are mainly attributed to the fact that the ionization probability becomes very small when the direction of emitted electrons is perpendicular to the direction of the XUV laser polarization;while for the rescattering ATI, the interference fringes on the spectrum mainly come from the superposition of the waist structures on the spectra of all sub-channels.
文摘In this paper, a comprehensive energy function is used to formulate the three most popular objective functions:Kapur's, Otsu and Tsalli's functions for performing effective multilevel color image thresholding. These new energy based objective criterions are further combined with the proficient search capability of swarm based algorithms to improve the efficiency and robustness. The proposed multilevel thresholding approach accurately determines the optimal threshold values by using generated energy curve, and acutely distinguishes different objects within the multi-channel complex images. The performance evaluation indices and experiments on different test images illustrate that Kapur's entropy aided with differential evolution and bacterial foraging optimization algorithm generates the most accurate and visually pleasing segmented images.
文摘In order to make the environment of palmprint recognition more flexible and improve the accuracy of touchless palmprint recognition. This paper proposes a robust, touchless, palmprint recognition system which is based on color palmprint images. This system uses skin-color thresholding and hand valley detection algorithm for extracting palmprint. Then, the local binary pattern (LBP) is applied to the palmprint in order to extract the palmprint features. Finally, chi square statistic is used for classification. The experimental results present the equal error rate of 3.7668% and correct recognition rate of 97.0142%. Therefore the results show that this approach is robust and efficient in color palmprint images which are acquired in lighting changes and cluttered background for touch-less palmprint recognition system.
文摘嵌入式设备中部署深度学习检测模型往往面临算力不足的问题,而感兴趣区域(ROI)提取可作为一种高效的性能优化手段。文章提出一种基于HSV(Hue,Saturation,Value)色彩空间模型的ROI提取的方法,将检测目标的像素信息转化到HSV色彩空间,在色相-饱和度(H-S)平面引入DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法,精确定位目标的主色彩像素在H-S平面上的分布位置,同时过滤杂乱色彩,然后通过Quickhull(快壳)凸包算法,从散点数据中拟合出主色彩的精确分布范围。根据获取的主色彩范围对像素进行遍历,可以根据色彩信息有效地提取ROI。实验结果表明,经过该方法优化后的Faster R-CNN(Faster Regions with Convolutional Neural Networks)算法,较原模型减少了57.08%的平均推理耗时,同时精确率提升了0.9百分点。这对于嵌入式设备中进行实时目标检测具有重要的现实意义。
