针对振动目标的激光微多普勒信号特征参数提取问题,引入一种新的时频分析方法即非线性匹配追踪算法(NMP),但该算法在强噪声和弱调制条件下存在较大局限性。由此提出一种加权平均频率算法(WAFA-NMP)对其抗噪性能进行改进,通过滑动矩形窗...针对振动目标的激光微多普勒信号特征参数提取问题,引入一种新的时频分析方法即非线性匹配追踪算法(NMP),但该算法在强噪声和弱调制条件下存在较大局限性。由此提出一种加权平均频率算法(WAFA-NMP)对其抗噪性能进行改进,通过滑动矩形窗对NMP所提取本征函数的瞬时频率和幅度进行加权平均,得到其对应的时频分布。同时,对于弱调制条件下参数提取困难的问题,提出欠采样的WAFA-NMP来提取弱调制下的微动参数。仿真实验表明,与Wigner-Ville分布及平滑伪Wigner-Ville分布比较,提出的WAFA-NMP方法性能更好,其平均估值精度高达96%,抗噪性能在-10 d B以上。展开更多
针对现有的视网膜血管分割方法对微细血管分割精度低的问题,在多尺度单通道线性追踪(MSLTA:Multi-Scale Single-Channel Linear Track)的图像分割方法基础上,提出了一种新的、有效的视网膜血管分割方法。采用Gabor滤波预处理以增强血管...针对现有的视网膜血管分割方法对微细血管分割精度低的问题,在多尺度单通道线性追踪(MSLTA:Multi-Scale Single-Channel Linear Track)的图像分割方法基础上,提出了一种新的、有效的视网膜血管分割方法。采用Gabor滤波预处理以增强血管信息,利用MSLTA算法获得最初的血管网络,采用连通域标记的去噪方法,去除图像上的斑点噪声,分割出最终的血管。利用国际上公开的DRIVE(Digital Retinal Images for Vessel Extraction)数据库的视网膜图像进行实验,并与现有的常规算法做了对比。多组实验结果表明,该方法的平均精确度达到95.37%,能很好地保留微细血管。展开更多
The study on seismic anisotropy is one of the difficult problems in the field of geophysics nowadays.As a method of ray theory,the seismic anisotropy ray tracing is an important means to study the anisotropic seismic ...The study on seismic anisotropy is one of the difficult problems in the field of geophysics nowadays.As a method of ray theory,the seismic anisotropy ray tracing is an important means to study the anisotropic seismic wave propagation. The traditional ray tracing system formulated in terms of elastic parameters in the anisotropy is more complicated than that in the isotropic case. Considering the difficulty,a kind of ray tracing system formulated in terms of phase velocity and group velocity is introduced. The new method is similar to the expressions for isotropic media,and avoids the trouble of determining the eigenvalue vector at each time. Besides the ray tracing numerical simulation of different models of vertical transversely isotropic( VTI) medium is carried out,in order to verify the accuracy and applicability of the method and further study the characteristics of wave field propagation in different VTI mediums. The study is certainly valuable in reference for later processing of the anisotropic seismic data.展开更多
The mode theory is the main way to study the propagation characteristics of light in fiber so far,but it is not suitable for analysis of light in duct.By using ray-tracing method,the rotary propagation characteristics...The mode theory is the main way to study the propagation characteristics of light in fiber so far,but it is not suitable for analysis of light in duct.By using ray-tracing method,the rotary propagation characteristics of light in multimode-single mode-multimode(MSM) fiber structures are analyzed in this paper.Firstly,the light ray in fiber can propagate around an inscribed circle,and the central axis of this fiber is the propagation axis.Secondly,the radius of the inscribed circle is decided by both incident angle and incident position,and its variation is between 0 and RM,where RM is the radius of the multimode fiber.Lastly,the bigger the ratio of core and cladding diameter is,the higher the propagation efficiency is.展开更多
文摘针对振动目标的激光微多普勒信号特征参数提取问题,引入一种新的时频分析方法即非线性匹配追踪算法(NMP),但该算法在强噪声和弱调制条件下存在较大局限性。由此提出一种加权平均频率算法(WAFA-NMP)对其抗噪性能进行改进,通过滑动矩形窗对NMP所提取本征函数的瞬时频率和幅度进行加权平均,得到其对应的时频分布。同时,对于弱调制条件下参数提取困难的问题,提出欠采样的WAFA-NMP来提取弱调制下的微动参数。仿真实验表明,与Wigner-Ville分布及平滑伪Wigner-Ville分布比较,提出的WAFA-NMP方法性能更好,其平均估值精度高达96%,抗噪性能在-10 d B以上。
文摘针对现有的视网膜血管分割方法对微细血管分割精度低的问题,在多尺度单通道线性追踪(MSLTA:Multi-Scale Single-Channel Linear Track)的图像分割方法基础上,提出了一种新的、有效的视网膜血管分割方法。采用Gabor滤波预处理以增强血管信息,利用MSLTA算法获得最初的血管网络,采用连通域标记的去噪方法,去除图像上的斑点噪声,分割出最终的血管。利用国际上公开的DRIVE(Digital Retinal Images for Vessel Extraction)数据库的视网膜图像进行实验,并与现有的常规算法做了对比。多组实验结果表明,该方法的平均精确度达到95.37%,能很好地保留微细血管。
文摘The study on seismic anisotropy is one of the difficult problems in the field of geophysics nowadays.As a method of ray theory,the seismic anisotropy ray tracing is an important means to study the anisotropic seismic wave propagation. The traditional ray tracing system formulated in terms of elastic parameters in the anisotropy is more complicated than that in the isotropic case. Considering the difficulty,a kind of ray tracing system formulated in terms of phase velocity and group velocity is introduced. The new method is similar to the expressions for isotropic media,and avoids the trouble of determining the eigenvalue vector at each time. Besides the ray tracing numerical simulation of different models of vertical transversely isotropic( VTI) medium is carried out,in order to verify the accuracy and applicability of the method and further study the characteristics of wave field propagation in different VTI mediums. The study is certainly valuable in reference for later processing of the anisotropic seismic data.
基金supported by the National Natural Science Foundation of China(No.61177076)the Fundamental Research Funds for the Central Universities(Nos.2013-Ia-038 and 2013-Ia-006)
文摘The mode theory is the main way to study the propagation characteristics of light in fiber so far,but it is not suitable for analysis of light in duct.By using ray-tracing method,the rotary propagation characteristics of light in multimode-single mode-multimode(MSM) fiber structures are analyzed in this paper.Firstly,the light ray in fiber can propagate around an inscribed circle,and the central axis of this fiber is the propagation axis.Secondly,the radius of the inscribed circle is decided by both incident angle and incident position,and its variation is between 0 and RM,where RM is the radius of the multimode fiber.Lastly,the bigger the ratio of core and cladding diameter is,the higher the propagation efficiency is.
