A multi-world mechanism is developed for modeling evolutionary design process from conceptual design to detailed design. In this mechanism, the evolutionary design database is represented by a sequence of worlds corre...A multi-world mechanism is developed for modeling evolutionary design process from conceptual design to detailed design. In this mechanism, the evolutionary design database is represented by a sequence of worlds corresponding to the design descriptions at different design stages. In each world, only the differences with its ancestor world are recorded. When the design descriptions in one world are changed, these changes are then propagated to its descendant worlds automatically. Case study is conducted to show the effectiveness of this evolutionary design database model.展开更多
After a relation scheme R is decomposed into the set of schemes ρ={R_1,...,R_n},we may pose queries as if R existed in the database,taking a join of R_i's,when it is necessary to implement the query.Suppose a que...After a relation scheme R is decomposed into the set of schemes ρ={R_1,...,R_n},we may pose queries as if R existed in the database,taking a join of R_i's,when it is necessary to implement the query.Suppose a query involves a set of attributes S(?)R,we want to find the smallest subset of ρ whose union includes S.We prove that the problem is NP-complete and present a polynomial-bounded approximation algorithm.A subset of ρ whose union includes S and has a decomposition into 3NF with a lossless join and preservation of dependencies is given in the paper.展开更多
It has been found that unknown meteor showers could be efficiently discovered from the single station video meteor database of the International Meteor Organization(IMO)by assuming the geocentric velocity and adjustin...It has been found that unknown meteor showers could be efficiently discovered from the single station video meteor database of the International Meteor Organization(IMO)by assuming the geocentric velocity and adjusting it within the dynamically permitted range.The mean geocentric velocities of new meteor showers can be obtained,as well as the coordinates of the radiants.The activity period and maximum time can also be obtained if there are sufficient shower meteors.All single station video meteor observations between February 13 and 17(from 2000 to 2005)in IMO's database are processed with this method.As a result,two new meteor showers,one near RA=245.10°,Dec=41.82°in Hercules and the other near RA=233.03°,Dec=17.04°in Serpenids,are discovered.Some dynamical characteristics of the new meteor showers are also determined.Considering the random nature on the selection of period in this work,it is expected that there are some more potential new meteor showers in IMO's video database.展开更多
基金Selected from Proceedings of the 7th Intemational Conference on Frontiers of Design and Manufacturing (ICFDM'2006).
文摘A multi-world mechanism is developed for modeling evolutionary design process from conceptual design to detailed design. In this mechanism, the evolutionary design database is represented by a sequence of worlds corresponding to the design descriptions at different design stages. In each world, only the differences with its ancestor world are recorded. When the design descriptions in one world are changed, these changes are then propagated to its descendant worlds automatically. Case study is conducted to show the effectiveness of this evolutionary design database model.
文摘After a relation scheme R is decomposed into the set of schemes ρ={R_1,...,R_n},we may pose queries as if R existed in the database,taking a join of R_i's,when it is necessary to implement the query.Suppose a query involves a set of attributes S(?)R,we want to find the smallest subset of ρ whose union includes S.We prove that the problem is NP-complete and present a polynomial-bounded approximation algorithm.A subset of ρ whose union includes S and has a decomposition into 3NF with a lossless join and preservation of dependencies is given in the paper.
基金the National Natural Science Foundation of China(Grant No.10373004)
文摘It has been found that unknown meteor showers could be efficiently discovered from the single station video meteor database of the International Meteor Organization(IMO)by assuming the geocentric velocity and adjusting it within the dynamically permitted range.The mean geocentric velocities of new meteor showers can be obtained,as well as the coordinates of the radiants.The activity period and maximum time can also be obtained if there are sufficient shower meteors.All single station video meteor observations between February 13 and 17(from 2000 to 2005)in IMO's database are processed with this method.As a result,two new meteor showers,one near RA=245.10°,Dec=41.82°in Hercules and the other near RA=233.03°,Dec=17.04°in Serpenids,are discovered.Some dynamical characteristics of the new meteor showers are also determined.Considering the random nature on the selection of period in this work,it is expected that there are some more potential new meteor showers in IMO's video database.
