针对ORB(oriented fast and rotated brief)算法提取图片特征时存在的特征点分布不均匀问题,提出了一种改进的ORB算法。通过密度峰值聚类算法计算四叉树分割后的各区域特征点密度峰值,并对密度峰值高的区域使用四叉树多次分割;同时在初...针对ORB(oriented fast and rotated brief)算法提取图片特征时存在的特征点分布不均匀问题,提出了一种改进的ORB算法。通过密度峰值聚类算法计算四叉树分割后的各区域特征点密度峰值,并对密度峰值高的区域使用四叉树多次分割;同时在初始阈值(iniThFAST)和最小阈值(minThFAST)中加入中间阈值(middleThFAST),提高特征点灰度值差值,减少冗余特征点提取,提高图片特征点均匀性。对特征点提取与匹配进行了实验验证,结果表明改进算法对比传统ORB算法在均匀度和匹配效率方面均有明显提升。结合ORB-SLAM2定位实验表明,改进算法的定位精度平均提高16.6%,每帧追踪时间平均减少12.4%,有效保证实际定位过程的精确性和实时性。展开更多
This paper focuses on the 2-median location improvement problem on tree networks and the problem is to modify the weights of edges at the minimum cost such that the overall sum of the weighted distance of the vertices...This paper focuses on the 2-median location improvement problem on tree networks and the problem is to modify the weights of edges at the minimum cost such that the overall sum of the weighted distance of the vertices to the respective closest one of two prescribed vertices in the modified network is upper bounded by a given value.l1 norm and l∞norm are used to measure the total modification cost. These two problems have a strong practical application background and important theoretical research value. It is shown that such problems can be transformed into a series of sum-type and bottleneck-type continuous knapsack problems respectively.Based on the property of the optimal solution two O n2 algorithms for solving the two problems are proposed where n is the number of vertices on the tree.展开更多
Investment casting has been widely recognized as the best option in producing TiAl components with key benefits of accuracy,versatility and integrity.The collapsibility of ceramic moulds for investment casting is crit...Investment casting has been widely recognized as the best option in producing TiAl components with key benefits of accuracy,versatility and integrity.The collapsibility of ceramic moulds for investment casting is critical in the manufacturing process of TiAl components due to TiAl's intrinsic brittleness at room temperature.The aim of the present research is to provide a method for production of TiAl components by investment casting in ZrO2 ceramic moulds with improved collapsibility.Slurries prepared with high polymer additions were utilized during the preparation of ceramic moulds.The stress/strain curves obtained from green and baked ceramic moulds demonstrate that the green strength was increased with the application of high polymer,while baked strength decreased,thus the collapsibility of ceramic moulds was improved.It is suggested that this result is related to the burn-out of high polymer which left a lot of cavities.The experimental findings were also verified by the investment casting of "I"-shaped TiAl components.展开更多
Gas flooding such as CO2 flooding may be effectively applied to ultra-low permeability reservoirs, but gas channeling is inevitable due to low viscosity and high mobility of gas and formation heterogeneity. In order t...Gas flooding such as CO2 flooding may be effectively applied to ultra-low permeability reservoirs, but gas channeling is inevitable due to low viscosity and high mobility of gas and formation heterogeneity. In order to mitigate or prevent gas channeling, ethylenediamine is chosen for permeability profile control. The reaction mechanism of ethylenediamine with CO2, injection performance, swept volume, and enhanced oil recovery were systematically evaluated. The reaction product of ethylenediamine and CO2 was a white solid or a light yellow viscous liquid, which would mitigate or prevent gas channeling. Also, ethylenediamine could be easily injected into ultra-low permeability cores at high temperature with protective ethanol slugs. The core was swept by injection of 0.3 PV ethylenediamine. Oil displacement tests performed on heterogeneous models with closed fractures, oil recovery was significantly enhanced with injection of ethylenediamine. Experimental results showed that using ethylenediamine to plug high permeability layers would provide a new research idea for the gas injection in fractured, heterogeneous and ultra-low permeability reservoirs. This technology has the potential to be widely applied in oilfields.展开更多
The Long March 2 F(LM-2F) launch vehicle, the only launch vehicle designed for manned space flight in China, successfully launched the Tiangong 2 space laboratory and the Shenzhou 11 manned spaceship into orbits in 20...The Long March 2 F(LM-2F) launch vehicle, the only launch vehicle designed for manned space flight in China, successfully launched the Tiangong 2 space laboratory and the Shenzhou 11 manned spaceship into orbits in 2016 respectively. In this study, it introduces the technological improvements for enhancing the reliability of the LM-2F launch vehicle in the aspects of general technology, control system, manufacture and ground support system. The LM-2F launch vehicle will continue to provide more contributions to the Chinese Space Station Project with its high reliability and 100% success rate.展开更多
文摘针对ORB(oriented fast and rotated brief)算法提取图片特征时存在的特征点分布不均匀问题,提出了一种改进的ORB算法。通过密度峰值聚类算法计算四叉树分割后的各区域特征点密度峰值,并对密度峰值高的区域使用四叉树多次分割;同时在初始阈值(iniThFAST)和最小阈值(minThFAST)中加入中间阈值(middleThFAST),提高特征点灰度值差值,减少冗余特征点提取,提高图片特征点均匀性。对特征点提取与匹配进行了实验验证,结果表明改进算法对比传统ORB算法在均匀度和匹配效率方面均有明显提升。结合ORB-SLAM2定位实验表明,改进算法的定位精度平均提高16.6%,每帧追踪时间平均减少12.4%,有效保证实际定位过程的精确性和实时性。
基金The National Natural Science Foundation of China(No.10801031)
文摘This paper focuses on the 2-median location improvement problem on tree networks and the problem is to modify the weights of edges at the minimum cost such that the overall sum of the weighted distance of the vertices to the respective closest one of two prescribed vertices in the modified network is upper bounded by a given value.l1 norm and l∞norm are used to measure the total modification cost. These two problems have a strong practical application background and important theoretical research value. It is shown that such problems can be transformed into a series of sum-type and bottleneck-type continuous knapsack problems respectively.Based on the property of the optimal solution two O n2 algorithms for solving the two problems are proposed where n is the number of vertices on the tree.
基金supported by the National Natural Science Foundation of China under grant No. 51001040the Specialized Research Fund for the Doctoral Program of Higher Education within project No. 200802130014+1 种基金the Fundamental Research Funds for the Central Universities (grant No. HIT NSRIF.2010116)the Development program for Outstanding Young Teachers in Harbin Institute of Technology (HITQNJS 2009022)
文摘Investment casting has been widely recognized as the best option in producing TiAl components with key benefits of accuracy,versatility and integrity.The collapsibility of ceramic moulds for investment casting is critical in the manufacturing process of TiAl components due to TiAl's intrinsic brittleness at room temperature.The aim of the present research is to provide a method for production of TiAl components by investment casting in ZrO2 ceramic moulds with improved collapsibility.Slurries prepared with high polymer additions were utilized during the preparation of ceramic moulds.The stress/strain curves obtained from green and baked ceramic moulds demonstrate that the green strength was increased with the application of high polymer,while baked strength decreased,thus the collapsibility of ceramic moulds was improved.It is suggested that this result is related to the burn-out of high polymer which left a lot of cavities.The experimental findings were also verified by the investment casting of "I"-shaped TiAl components.
基金Financial support for this work from National Sciencetechnology Support Plan Projects (No. 2012BAC26B00)the Science Foundation of China University of Petroleum, Beijing (No.2462012KYJJ23)
文摘Gas flooding such as CO2 flooding may be effectively applied to ultra-low permeability reservoirs, but gas channeling is inevitable due to low viscosity and high mobility of gas and formation heterogeneity. In order to mitigate or prevent gas channeling, ethylenediamine is chosen for permeability profile control. The reaction mechanism of ethylenediamine with CO2, injection performance, swept volume, and enhanced oil recovery were systematically evaluated. The reaction product of ethylenediamine and CO2 was a white solid or a light yellow viscous liquid, which would mitigate or prevent gas channeling. Also, ethylenediamine could be easily injected into ultra-low permeability cores at high temperature with protective ethanol slugs. The core was swept by injection of 0.3 PV ethylenediamine. Oil displacement tests performed on heterogeneous models with closed fractures, oil recovery was significantly enhanced with injection of ethylenediamine. Experimental results showed that using ethylenediamine to plug high permeability layers would provide a new research idea for the gas injection in fractured, heterogeneous and ultra-low permeability reservoirs. This technology has the potential to be widely applied in oilfields.
文摘The Long March 2 F(LM-2F) launch vehicle, the only launch vehicle designed for manned space flight in China, successfully launched the Tiangong 2 space laboratory and the Shenzhou 11 manned spaceship into orbits in 2016 respectively. In this study, it introduces the technological improvements for enhancing the reliability of the LM-2F launch vehicle in the aspects of general technology, control system, manufacture and ground support system. The LM-2F launch vehicle will continue to provide more contributions to the Chinese Space Station Project with its high reliability and 100% success rate.
