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RISS 인기검색어
- 검색키워드
- 저자 : Qingqing Ke (검색결과 3 건)
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Detection of Seam Carved Image Based on Additional Seam Carving Behavior
Yongzhen Ke,Qingqing Shan,Fan Qin,Weidong Min,Jing Guo 보안공학연구지원센터 2016 International Journal of Signal Processing, Image Vol.9 No.2
Seam carving is a kind of content aware image retargeting algorithm and can be applied to resize and deliberately remove objects from digital images. Based on the observation that after applying an additional seam carving operation, the similarity, the energy relative error, and the difference of seam distance of original image are quite different from those of the seam-carved image, we propose and develop a new method for detecting seam carving or seam insertion of natural images without knowledge of the original image. First, we apply an additional seam carving operation to the testing image, then calculate similarity, energy relative error, and difference of seam distance between the testing image and its seam carved version. Last, we extract 11 dimensional features to detect seam carving operation to train a support vector machine classifier for recognizing whether an image is an original or it has been modified using seam-carving. Our experimental results demonstrate that our proposed forensic method achieves not only better detection rate but also lower dimensional features compared with other existing seam carved detection methods.
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Fundamental issues of applications of C/SiC composites for re-entry vehicles
Yani Zhang,Litong Zhang,Hui Mei,Qingqing Ke,Yongdong Xu,Laifei Cheng 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.3
Carbon fiber reinforced silicon carbide ceramic matrix composite materials (C/SiCs) are being tested for hot structures and thermal protection systems (TPS) of launch vehicles and spacecraft, and also for advanced friction system of aircraft and racing cars. A number of tribological and joining components are required in these applications, such as bushing and rolling contact bearings, nuts and bolts, which require excellent mechanical, physical and chemical properties at temperatures higher than 1650℃. This study summarizes preparation of C/SiC load-carrying bearings for hinge by the Chemical Vapor Infiltration (CVI) method and C/SiC bolts for joints by the CVI + PIP (Polymer Impregnation and Pyrolysis) methods. The hinge bearing and bolts were examined in a simulated re-entry environment. Stress-oxidation was investigated under different stress levels from 0 to 200MPa up to 1800℃. The friction behavior of the hinge bearing system was studied under high loads (up to 25 kN) and low rotating velocities. The mechanical properties of the bolts with a thread connection were conducted under tensile and shear fatigue at both room temperature and elevated temperature. The results show that the stress-oxidation behavior of 2D-C/SiC composites in a combustion environment is a combined effect of extremely high load, high temperature, and oxidation. The load and temperature influenced the crack openings and thus the oxidation of carbon fibers in the precracked composites. The combustion environment mainly determined the time to failure of the specimens by oxidation damage under a high applied stress. Reliable thermal load-carrying ability and stable friction performance of the hinge bearing is demonstrated in high-temperature combustion environments with extremely high loads. The oxidation products of SiO2 at high temperatures between surfaces played an important role to modifies the friction by providing a protective layer. The room temperature tensile and shear strength of the bolts made of needled C/SiC are 139 MPa and 83 MPa, respectively. Even at 1800℃ in a combustion environment, the strengths still retained about 116MPa with a maximum decrease of 13%. More importantly, the bolts did not suffer significant mechanical degradation after tension-tension fatigue at 1 Hz for 24 h. Carbon fiber reinforced silicon carbide ceramic matrix composite materials (C/SiCs) are being tested for hot structures and thermal protection systems (TPS) of launch vehicles and spacecraft, and also for advanced friction system of aircraft and racing cars. A number of tribological and joining components are required in these applications, such as bushing and rolling contact bearings, nuts and bolts, which require excellent mechanical, physical and chemical properties at temperatures higher than 1650℃. This study summarizes preparation of C/SiC load-carrying bearings for hinge by the Chemical Vapor Infiltration (CVI) method and C/SiC bolts for joints by the CVI + PIP (Polymer Impregnation and Pyrolysis) methods. The hinge bearing and bolts were examined in a simulated re-entry environment. Stress-oxidation was investigated under different stress levels from 0 to 200MPa up to 1800℃. The friction behavior of the hinge bearing system was studied under high loads (up to 25 kN) and low rotating velocities. The mechanical properties of the bolts with a thread connection were conducted under tensile and shear fatigue at both room temperature and elevated temperature. The results show that the stress-oxidation behavior of 2D-C/SiC composites in a combustion environment is a combined effect of extremely high load, high temperature, and oxidation. The load and temperature influenced the crack openings and thus the oxidation of carbon fibers in the precracked composites. The combustion environment mainly determined the time to failure of the specimens by oxidation damage under a high applied stress. Reliable thermal load-carrying ability and stable friction performance of the hinge bearing is demonstrated in high-temperature combustion environments with extremely high loads. The oxidation products of SiO2 at high temperatures between surfaces played an important role to modifies the friction by providing a protective layer. The room temperature tensile and shear strength of the bolts made of needled C/SiC are 139 MPa and 83 MPa, respectively. Even at 1800℃ in a combustion environment, the strengths still retained about 116MPa with a maximum decrease of 13%. More importantly, the bolts did not suffer significant mechanical degradation after tension-tension fatigue at 1 Hz for 24 h.
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