In this work, the numerical analysis and experimental measurements were made to investigate the development of top-hat flow field at atmospheric pressure in a circular symmetrical subsonic nozzle. Measurements were ca...In this work, the numerical analysis and experimental measurements were made to investigate the development of top-hat flow field at atmospheric pressure in a circular symmetrical subsonic nozzle. Measurements were carried out over a range of inlet velocities(about 0.07–7 m/s) based on a nozzle with constant geometric parameters, which also provided verification for the numerical simulation. The objective of this study was to determine the change of top-hat flow field from the well-known pipe velocity profile to the saddle-back distribution as well as the key behaviours for the process. Results revealed a close coupling relationship between the process and the pressure gradient inside nozzle. It was concluded that the local flow direction of fluid near the edge of cross section was changed by static pressure gradient and overlapped with the mainstream. The increase in kinetic energy of each gas particle on the cross section was different contributed to the formation of top-hat flow field. The saddle-back distribution seems to occur after the appearance of the critical position. In addition, the influence of inlet velocity on the location of critical position as well as the degree of saddle-back distribution was also concerned.展开更多
Medical imaging includes different modalities and processes to visualize the interior of human body for diagnostic and treatment purpose. However, one of the most common degradations in medical images is their poor co...Medical imaging includes different modalities and processes to visualize the interior of human body for diagnostic and treatment purpose. However, one of the most common degradations in medical images is their poor contrast quality and noise. The existence of several objects and the close proximity of adjacent pixels values make the diagnostic process a daunting task. The idea of image enhancement techniques is to improve the quality of an image. In this study, morphological transform operation is carried out on medical images to enhance the contrast and quality. A disk shaped mask is used in Top-Hat and Bottom-Hat transform and this mask plays a vital role in the operation. Different types and sizes of medical images need different masks so that they can be successfully enhanced. The method shown in this study takes a mask of an arbitrary size and keeps changing its size until an optimum enhanced image is obtained from the transformation operation. The enhancement is achieved via an iterative exfoliation process. The results indicate that this method improves the contrast of medical images and can help with better diagnosis.展开更多
A low-energy ion spectrometer(LEIS) for use aboard three-axis stabilized spacecraft has been developed to measure ion energy per charge distribution in three-dimensional space with good energy-, angular-and temporal-r...A low-energy ion spectrometer(LEIS) for use aboard three-axis stabilized spacecraft has been developed to measure ion energy per charge distribution in three-dimensional space with good energy-, angular-and temporal-resolutions. For the standard top-hat electrostatic analyzer used widely in space plasma detection, three-axis stabilized spacecraft makes it difficult to obtain complete coverage of all possible ion arrival directions. We have designed angular scanning deflectors supplementing to a cylindrically symmetric top-hat electrostatic analyzer to provide a half-space field of view as 360°×90°(–45°–+45°), and fabricated the LEIS flight model for detecting magnetospheric ions in geosynchronous orbit. The performance of this payload has been evaluated in detail by a series of simulation and environmental tests, and the payload has also been calibrated through laboratory experiments using a low-energy ion source. The results show that capabilities of the LEIS payload are in accordance with the requirements of a magnetospheric mission.展开更多
In this paper, a new method for discovering the candidate car license plate locations is presented. First, the image is decomposed using a Haar wavelet to get the HL band with vertical edges. Then, the HL band image i...In this paper, a new method for discovering the candidate car license plate locations is presented. First, the image is decomposed using a Haar wavelet to get the HL band with vertical edges. Then, the HL band image is binarized using an Otsu threshold. Next a black top-hat algorithm is applied to reduce the effects of interfering large continuous features other than the license plate. At this time, a moving window based modified variance score calculation is made for areas with white pixels. This work found that the top 3 detected rectangle windows correctly locate the license plate regions with a success rate of about 98.2%. Moreover, the proposed method is robust enough to locate the plates in cases where the rough vehicle position has not been previously discovered and the cars are not centered in the image.展开更多
基金supported by the National Key Research and Development Program of China “Research and application of national quality infrastructure” (.No 2017YFF0205305)
文摘In this work, the numerical analysis and experimental measurements were made to investigate the development of top-hat flow field at atmospheric pressure in a circular symmetrical subsonic nozzle. Measurements were carried out over a range of inlet velocities(about 0.07–7 m/s) based on a nozzle with constant geometric parameters, which also provided verification for the numerical simulation. The objective of this study was to determine the change of top-hat flow field from the well-known pipe velocity profile to the saddle-back distribution as well as the key behaviours for the process. Results revealed a close coupling relationship between the process and the pressure gradient inside nozzle. It was concluded that the local flow direction of fluid near the edge of cross section was changed by static pressure gradient and overlapped with the mainstream. The increase in kinetic energy of each gas particle on the cross section was different contributed to the formation of top-hat flow field. The saddle-back distribution seems to occur after the appearance of the critical position. In addition, the influence of inlet velocity on the location of critical position as well as the degree of saddle-back distribution was also concerned.
文摘Medical imaging includes different modalities and processes to visualize the interior of human body for diagnostic and treatment purpose. However, one of the most common degradations in medical images is their poor contrast quality and noise. The existence of several objects and the close proximity of adjacent pixels values make the diagnostic process a daunting task. The idea of image enhancement techniques is to improve the quality of an image. In this study, morphological transform operation is carried out on medical images to enhance the contrast and quality. A disk shaped mask is used in Top-Hat and Bottom-Hat transform and this mask plays a vital role in the operation. Different types and sizes of medical images need different masks so that they can be successfully enhanced. The method shown in this study takes a mask of an arbitrary size and keeps changing its size until an optimum enhanced image is obtained from the transformation operation. The enhancement is achieved via an iterative exfoliation process. The results indicate that this method improves the contrast of medical images and can help with better diagnosis.
基金supported by the National Natural Science Foundation of China(Grant No.41327802)the CAS Key Research Program of Frontier Sciences(Grant No.QYZDB-SSW-DQC015)
文摘A low-energy ion spectrometer(LEIS) for use aboard three-axis stabilized spacecraft has been developed to measure ion energy per charge distribution in three-dimensional space with good energy-, angular-and temporal-resolutions. For the standard top-hat electrostatic analyzer used widely in space plasma detection, three-axis stabilized spacecraft makes it difficult to obtain complete coverage of all possible ion arrival directions. We have designed angular scanning deflectors supplementing to a cylindrically symmetric top-hat electrostatic analyzer to provide a half-space field of view as 360°×90°(–45°–+45°), and fabricated the LEIS flight model for detecting magnetospheric ions in geosynchronous orbit. The performance of this payload has been evaluated in detail by a series of simulation and environmental tests, and the payload has also been calibrated through laboratory experiments using a low-energy ion source. The results show that capabilities of the LEIS payload are in accordance with the requirements of a magnetospheric mission.
文摘In this paper, a new method for discovering the candidate car license plate locations is presented. First, the image is decomposed using a Haar wavelet to get the HL band with vertical edges. Then, the HL band image is binarized using an Otsu threshold. Next a black top-hat algorithm is applied to reduce the effects of interfering large continuous features other than the license plate. At this time, a moving window based modified variance score calculation is made for areas with white pixels. This work found that the top 3 detected rectangle windows correctly locate the license plate regions with a success rate of about 98.2%. Moreover, the proposed method is robust enough to locate the plates in cases where the rough vehicle position has not been previously discovered and the cars are not centered in the image.
