Cultures throughout the world are associating with the rivers.People depend upon the rivers and their tributaries for food,water,transport,and many other aspects of their daily lives.Unfortunately,human beings have no...Cultures throughout the world are associating with the rivers.People depend upon the rivers and their tributaries for food,water,transport,and many other aspects of their daily lives.Unfortunately,human beings have not calculated the accurate lengths for the great rivers even today.The lengths of the rivers are very different in popular textbooks,magazines,atlases and encyclopedias,etc.To accurately determine the lengths of the principal rivers of the world,the combination of satellite image analysis and field investigations to the source regions is proposed in this paper.The lengths of the Nile,Amazon,Yangtze,Mississippi,Yellow,Ob,Yenisey,Amur,Congo and Mekong,with lengths over or close to 5000 km,were calculated using the proposed method.The results may represent the most reliable and accurate lengths of the principal rivers of the world that are currently achievable.展开更多
In description logic,axiom pinpointing is used to explore defects in ontologies and identify hidden justifications for a logical consequence.In recent years,SAT-based axiom pinpointing techniques,which rely on the enu...In description logic,axiom pinpointing is used to explore defects in ontologies and identify hidden justifications for a logical consequence.In recent years,SAT-based axiom pinpointing techniques,which rely on the enumeration of minimal unsatisfiable subsets(MUSes)of pinpointing formulas,have gained increasing attention.Compared with traditional Tableau-based reasoning approaches,SAT-based techniques are more competitive when computing justifications for consequences in large-scale lightweight description logic ontologies.In this article,we propose a novel enumeration justification algorithm,working with a replicated driver.The replicated driver discovers new justifications from the explored justifications through cheap literals resolution,which avoids frequent calls of SAT solver.Moreover,when the use of SAT solver is inevitable,we adjust the strategies and heuristic parameters of the built-in SAT solver of axiom pinpointing algorithm.The adjusted SAT solver is able to improve the checking efficiency of unexplored sub-formulas.Our proposed method is implemented as a tool named RDMinA.The experimental results show that RDMinA outperforms the existing axiom pinpointing tools on practical biomedical ontologies such as Gene,Galen,NCI and Snomed-CT.展开更多
Purpose: Cylindrical ionization chambers as the PinPoint and the CC01 have high-spatial resolution and cylindrical symmetry in relevance to small fields. Dosimetry of newly advanced technologies that include non-copla...Purpose: Cylindrical ionization chambers as the PinPoint and the CC01 have high-spatial resolution and cylindrical symmetry in relevance to small fields. Dosimetry of newly advanced technologies that include non-coplanar beams, such as in Gamma-Knife, VMAT and IMRT treatment plans, the angular dependence of the ion chamber is essential. Therefore in this study we simulated two common used ion chambers using a Monte Carlo method. Methods: The angular dependence for the CC01 and the PinPoint were calculated for a vast angular range in a cylindrical water phantom for two LINAC photon beams, 6 MV and 15 MV. The calculations were performed for fully structural description of each ion chamber using Monte Carlo code, in order to reveal unsymmetrical response dose higher than 2% in medical applications. The calculated dose response, for the CC01 ion chamber, was validated with measurements. Results: The CC01 ion chamber showed a very small angular dependence compared to the PinPoint ion chamber. The relative angular dependence amplitude of the PinPoint was about 12% in the range of 0° - 110°. Conclusions: The differences in the ion chambers structure led to the variations in the relative angular dependence amplitude. Therefore, when choosing a detector, not only the volume of the ionization chamber but also its structure must be taken into consideration.展开更多
This paper summarizes the autonomous guidance methods(AGMs)for pinpoint soft landing on celestial surfaces.We first review the development of powered descent guidance methods,focusing on their contributions for dealin...This paper summarizes the autonomous guidance methods(AGMs)for pinpoint soft landing on celestial surfaces.We first review the development of powered descent guidance methods,focusing on their contributions for dealing with constraints and enhancing computational efficiency.With the increasing demand for reusable launchers and more scientific returns from space exploration,pinpoint soft landing has become a basic requirement.Unlike the kilometer-level precision for previous activities,the position accuracy of future planetary landers is within tens of meters of a target respecting all constraints of velocity and attitude,which is a very difficult task and arouses renewed interest in AGMs.This paper states the generalized three-and six-degree-of-freedom optimization problems in the powered descent phase and compares the features of three typical scenarios,i.e.,the lunar,Mars,and Earth landing.On this basis,the paper details the characteristics and adaptability of AGMs by comparing aspects of analytical guidance methods,numerical optimization algorithms,and learning-based methods,and discusses the convexification treatment and solution strategies for non-convex problems.Three key issues related to AGM application,including physical feasibility,model accuracy,and real-time performance,are presented afterward for discussion.Many space organizations,such as those in the United States,China,France,Germany,and Japan,have also developed free-flying demonstrators to carry out related research.The guidance methods which have been tested on these demonstrators are briefly introduced at the end of the paper.展开更多
基金supported by China High-Tech Research and Development Project(863 Project)the Innovation Project of Chinese Academy of Sciences,the Special Funds of Director General of Institute of Remote Sensing Applications,Chinese Academy of Sciences,the Funds of the State Key Laboratory of Remote Sensing Sciences of Chinathe Funds of the State Key Laboratory of Information Engineering in Surveying,Mapping and Remote Sensing of China and Earth&Space Awards of the Earth and Space Foundation.
文摘Cultures throughout the world are associating with the rivers.People depend upon the rivers and their tributaries for food,water,transport,and many other aspects of their daily lives.Unfortunately,human beings have not calculated the accurate lengths for the great rivers even today.The lengths of the rivers are very different in popular textbooks,magazines,atlases and encyclopedias,etc.To accurately determine the lengths of the principal rivers of the world,the combination of satellite image analysis and field investigations to the source regions is proposed in this paper.The lengths of the Nile,Amazon,Yangtze,Mississippi,Yellow,Ob,Yenisey,Amur,Congo and Mekong,with lengths over or close to 5000 km,were calculated using the proposed method.The results may represent the most reliable and accurate lengths of the principal rivers of the world that are currently achievable.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.42050103,62076108,and U19A2061).
文摘In description logic,axiom pinpointing is used to explore defects in ontologies and identify hidden justifications for a logical consequence.In recent years,SAT-based axiom pinpointing techniques,which rely on the enumeration of minimal unsatisfiable subsets(MUSes)of pinpointing formulas,have gained increasing attention.Compared with traditional Tableau-based reasoning approaches,SAT-based techniques are more competitive when computing justifications for consequences in large-scale lightweight description logic ontologies.In this article,we propose a novel enumeration justification algorithm,working with a replicated driver.The replicated driver discovers new justifications from the explored justifications through cheap literals resolution,which avoids frequent calls of SAT solver.Moreover,when the use of SAT solver is inevitable,we adjust the strategies and heuristic parameters of the built-in SAT solver of axiom pinpointing algorithm.The adjusted SAT solver is able to improve the checking efficiency of unexplored sub-formulas.Our proposed method is implemented as a tool named RDMinA.The experimental results show that RDMinA outperforms the existing axiom pinpointing tools on practical biomedical ontologies such as Gene,Galen,NCI and Snomed-CT.
文摘Purpose: Cylindrical ionization chambers as the PinPoint and the CC01 have high-spatial resolution and cylindrical symmetry in relevance to small fields. Dosimetry of newly advanced technologies that include non-coplanar beams, such as in Gamma-Knife, VMAT and IMRT treatment plans, the angular dependence of the ion chamber is essential. Therefore in this study we simulated two common used ion chambers using a Monte Carlo method. Methods: The angular dependence for the CC01 and the PinPoint were calculated for a vast angular range in a cylindrical water phantom for two LINAC photon beams, 6 MV and 15 MV. The calculations were performed for fully structural description of each ion chamber using Monte Carlo code, in order to reveal unsymmetrical response dose higher than 2% in medical applications. The calculated dose response, for the CC01 ion chamber, was validated with measurements. Results: The CC01 ion chamber showed a very small angular dependence compared to the PinPoint ion chamber. The relative angular dependence amplitude of the PinPoint was about 12% in the range of 0° - 110°. Conclusions: The differences in the ion chambers structure led to the variations in the relative angular dependence amplitude. Therefore, when choosing a detector, not only the volume of the ionization chamber but also its structure must be taken into consideration.
基金Project supported by the National Natural Science Foundation of China(No.61773341)the International Academy of Astronautics Study Group SG 3.32。
文摘This paper summarizes the autonomous guidance methods(AGMs)for pinpoint soft landing on celestial surfaces.We first review the development of powered descent guidance methods,focusing on their contributions for dealing with constraints and enhancing computational efficiency.With the increasing demand for reusable launchers and more scientific returns from space exploration,pinpoint soft landing has become a basic requirement.Unlike the kilometer-level precision for previous activities,the position accuracy of future planetary landers is within tens of meters of a target respecting all constraints of velocity and attitude,which is a very difficult task and arouses renewed interest in AGMs.This paper states the generalized three-and six-degree-of-freedom optimization problems in the powered descent phase and compares the features of three typical scenarios,i.e.,the lunar,Mars,and Earth landing.On this basis,the paper details the characteristics and adaptability of AGMs by comparing aspects of analytical guidance methods,numerical optimization algorithms,and learning-based methods,and discusses the convexification treatment and solution strategies for non-convex problems.Three key issues related to AGM application,including physical feasibility,model accuracy,and real-time performance,are presented afterward for discussion.Many space organizations,such as those in the United States,China,France,Germany,and Japan,have also developed free-flying demonstrators to carry out related research.The guidance methods which have been tested on these demonstrators are briefly introduced at the end of the paper.
