The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the ...The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterbome modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.展开更多
The phase of cross-correlation function of two different normal modes contains source range information, which can be extracted by warping transform due to the dispersive characteristics of the shallow water waveguide...The phase of cross-correlation function of two different normal modes contains source range information, which can be extracted by warping transform due to the dispersive characteristics of the shallow water waveguide. The autocorrelation function of the received pressure or particle velocity contains both modal autocorrelation component(MAC) and modal cross-correlation component(MCC), with the former part usually treated as interference for source ranging. Because the real part of the vertical intensity flux(RPVIF) only contains MCC, a passive impulsive source ranging method based on the frequency warping transform of RPVIF with a single vector receiver in shallow water is presented. Using a waveguide-invariant-based frequency warping operator, the cross-correlation components of two different modes in the vertical intensity flux are warped into separable impulsive sequences, the time delays of which are subsequently used for source ranging. The advantages of source ranging based on warping the vertical intensity flux compared with warping the pressure autocorrelation function are pointed out, and the experiment results are also presented.展开更多
In this paper, a new semi-analytical and semi-engineering method of the closed form solution of stress intensity factors （SIFs） of cracks emanating from a surface semi-spherical cavity in a finite body is derived us...In this paper, a new semi-analytical and semi-engineering method of the closed form solution of stress intensity factors （SIFs） of cracks emanating from a surface semi-spherical cavity in a finite body is derived using the energy release rate theory. A mode of crack opening displacements of a normal slice is established, and the normal slice relevant functions are introduced. The proposed method is both effective and accurate for the problem of three-dimensional cracks emanating from a surface cavity. A series of useful results of SIFs are obtained.展开更多
This article introduces a new normalized nonlocal hybrid level set method for image segmentation.Due to intensity overlapping,blurred edges with complex backgrounds,simple intensity and texture information,such kind o...This article introduces a new normalized nonlocal hybrid level set method for image segmentation.Due to intensity overlapping,blurred edges with complex backgrounds,simple intensity and texture information,such kind of image segmentation is still a challenging task.The proposed method uses both the region and boundary information to achieve accurate segmentation results.The region information can help to identify rough region of interest and prevent the boundary leakage problem.It makes use of normalized nonlocal comparisons between pairs of patches in each region,and a heuristic intensity model is proposed to suppress irrelevant strong edges and constrain the segmentation.The boundary information can help to detect the precise location of the target object,it makes use of the geodesic active contour model to obtain the target boundary.The corresponding variational segmentation problem is implemented by a level set formulation.We use an internal energy term for geometric active contours to penalize the deviation of the level set function from a signed distance function.At last,experimental results on synthetic images and real images are shown in the paper with promising results.展开更多
The drop in the MRI signal intensity, analysed without any normalisation, was found related to the intervertebral disc degeneration, but its association with low back pain remains controversial. The authors developed ...The drop in the MRI signal intensity, analysed without any normalisation, was found related to the intervertebral disc degeneration, but its association with low back pain remains controversial. The authors developed the analysis of MR signal intensity distribution (AMRSID) method that analyzes the 3D distribution of the normalized T2-weighted MR signal intensity within the intervertebral disc using descriptive statistics of histograms and weighted centers. In this study, we hypothesized that the distribution of the normalized MRI signal intensity within T2- weighted images of the intervertebral disc is a bio-marker of low back pain (LBP) independently of age and disc degenerescence. The aims were to: 1) characterize intervertebral disc degeneration in vertebral fracture from MR T1-weighted and T2-weighted images;2) evaluate the sensitivity of the normalized MRI signal distribution to the presence of LBP, discs height loss and aging. We prospectively studied 22 patients who underwent an MRI acquisition within 48h after an accidental lumbar vertebral fracture. The presence of prefracture low back pain, spinal stenosis, annular disruption, intervertebral disc height loss was noted from each patient’s medical record. The presence of Modic changes, High-Intensity Zones (HIZs) and vertebral endplate perforations was recorded from MRI. The descriptive statistics of the normalized T2-weighted signal were compared using one-way ANOVAs and a principal component analysis was proposed. MRI, associated to normalisation of the signal intensity and principal component analysis, offers a remarkable potential for in-vivo imaging and analysis of vertebral fractures and adjacent tissues for the patient’s follow-up. The mean normalized MRI signal intensity of the adjacent intervertebral disc to the vertebral fracture was found to be a bio-marker of pain, independently of age and disc degeneration. However, the parameters describing the distribution of the normalized signal intensity were found to be not sensitive to the presence of low back pain, discs height loss and aging. Further studies need to be performed to detect small abnormalities that may explain the presence of LBP.展开更多
The calculation of absolute intensities of γ-rays arising from (ε+β+) decay is introduced briefly. Some examples are given to illustrate their applications. And some discussions are also made in the text.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11434012 and 41561144006)
文摘The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterbome modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.
基金Project supported by the Frontier Science Research of Chinese Academy of Sciences(Grant No.QYZDY-SSW-SLH005)
文摘The phase of cross-correlation function of two different normal modes contains source range information, which can be extracted by warping transform due to the dispersive characteristics of the shallow water waveguide. The autocorrelation function of the received pressure or particle velocity contains both modal autocorrelation component(MAC) and modal cross-correlation component(MCC), with the former part usually treated as interference for source ranging. Because the real part of the vertical intensity flux(RPVIF) only contains MCC, a passive impulsive source ranging method based on the frequency warping transform of RPVIF with a single vector receiver in shallow water is presented. Using a waveguide-invariant-based frequency warping operator, the cross-correlation components of two different modes in the vertical intensity flux are warped into separable impulsive sequences, the time delays of which are subsequently used for source ranging. The advantages of source ranging based on warping the vertical intensity flux compared with warping the pressure autocorrelation function are pointed out, and the experiment results are also presented.
文摘In this paper, a new semi-analytical and semi-engineering method of the closed form solution of stress intensity factors （SIFs） of cracks emanating from a surface semi-spherical cavity in a finite body is derived using the energy release rate theory. A mode of crack opening displacements of a normal slice is established, and the normal slice relevant functions are introduced. The proposed method is both effective and accurate for the problem of three-dimensional cracks emanating from a surface cavity. A series of useful results of SIFs are obtained.
基金supported in part by the National Natural Science Foundation of China(11626214,11571309)the General Research Project of Zhejiang Provincial Department of Education(Y201635378)+3 种基金the Zhejiang Provincial Natural Science Foundation of China(LY17F020011)J.Peng is supported by the National Natural Science Foundation of China(11771160)the Research Promotion Program of Huaqiao University(ZQN-PY411)Natural Science Foundation of Fujian Province(2015J01254)
文摘This article introduces a new normalized nonlocal hybrid level set method for image segmentation.Due to intensity overlapping,blurred edges with complex backgrounds,simple intensity and texture information,such kind of image segmentation is still a challenging task.The proposed method uses both the region and boundary information to achieve accurate segmentation results.The region information can help to identify rough region of interest and prevent the boundary leakage problem.It makes use of normalized nonlocal comparisons between pairs of patches in each region,and a heuristic intensity model is proposed to suppress irrelevant strong edges and constrain the segmentation.The boundary information can help to detect the precise location of the target object,it makes use of the geodesic active contour model to obtain the target boundary.The corresponding variational segmentation problem is implemented by a level set formulation.We use an internal energy term for geometric active contours to penalize the deviation of the level set function from a signed distance function.At last,experimental results on synthetic images and real images are shown in the paper with promising results.
文摘The drop in the MRI signal intensity, analysed without any normalisation, was found related to the intervertebral disc degeneration, but its association with low back pain remains controversial. The authors developed the analysis of MR signal intensity distribution (AMRSID) method that analyzes the 3D distribution of the normalized T2-weighted MR signal intensity within the intervertebral disc using descriptive statistics of histograms and weighted centers. In this study, we hypothesized that the distribution of the normalized MRI signal intensity within T2- weighted images of the intervertebral disc is a bio-marker of low back pain (LBP) independently of age and disc degenerescence. The aims were to: 1) characterize intervertebral disc degeneration in vertebral fracture from MR T1-weighted and T2-weighted images;2) evaluate the sensitivity of the normalized MRI signal distribution to the presence of LBP, discs height loss and aging. We prospectively studied 22 patients who underwent an MRI acquisition within 48h after an accidental lumbar vertebral fracture. The presence of prefracture low back pain, spinal stenosis, annular disruption, intervertebral disc height loss was noted from each patient’s medical record. The presence of Modic changes, High-Intensity Zones (HIZs) and vertebral endplate perforations was recorded from MRI. The descriptive statistics of the normalized T2-weighted signal were compared using one-way ANOVAs and a principal component analysis was proposed. MRI, associated to normalisation of the signal intensity and principal component analysis, offers a remarkable potential for in-vivo imaging and analysis of vertebral fractures and adjacent tissues for the patient’s follow-up. The mean normalized MRI signal intensity of the adjacent intervertebral disc to the vertebral fracture was found to be a bio-marker of pain, independently of age and disc degeneration. However, the parameters describing the distribution of the normalized signal intensity were found to be not sensitive to the presence of low back pain, discs height loss and aging. Further studies need to be performed to detect small abnormalities that may explain the presence of LBP.
文摘The calculation of absolute intensities of γ-rays arising from (ε+β+) decay is introduced briefly. Some examples are given to illustrate their applications. And some discussions are also made in the text.
