Effect of hydro co-extrusion on microstructure of duo-cast Al 3003/Al 4004 clad materials

The effects of hydro co-extrusion on the microstructure changes of aluminum hybrid duo-cast Al 3003/Al 4004 clad materials were studied. The specimen of duo-cast Al 3003/Al 4004 clad materials was in circle shape, and was composed of Al 3003(outside) and Al 4004(inside) materials. The specimen was extruded by the hydro co-extrusion equipment. The manufacturing conditions of the specimen were 423 K in temperature and 5 in extrusion ratio. The dimensions of the specimen were 80 mm in diameter of the Al 4004 material and 35 mm in thickness of the Al 3003 material before the hydro co-extrusion process, and 30 mm in diameter and about 5 mm in thickness after the extrusion process, respectively. The microstructure and the hardness for two specimens were investigated. The hardness value of cross section in the duo-cast Al 3003/Al 4004 clad materials before the extrusion process was increased in form of the parabola toward the center. However, after the extrusion process, it was almost constant in the portion of Al 4004 material. Lots of big voids above 1 mm in diameter in the specimen existed in the interfacing region of Al 3003 and Al 4004 materials before the extrusion process. These big voids disappeared after the process of hydro co-extrusion.     

CTPR*-Link Tree :An Efficient Implementation on Indexing the Moving Object in Spatio-Temporal Database

1IntroductionSpatio-temporal database systems have developed dra-matically both in theory and in practice .Spatio-tempo-ral database deals with objects which change their loca-tion with the ti me[1].In term of indexing the currentand future positions of moving objects , the TPR*-tree[2]outperforms other indexing trees[3],such as PR-tree[4], NSI[5], and STAR-tree[6]both in theory andpractice . What s more ,the TPR*-tree canspeed up da-ta access if it is designed as main memory-based index…     

一种智能选择多维位置数据的移动定位体系结构

通过动态获取和发送移动终端相关的位置信息，下一代移动通信网络（3G／4G）能提供一个较广范围的新应用。移动网络现在能越来越准确地确定终端的位置，使得时移动终端提供移动定位服务（MLS）成为可能。提出了一个与定位服务相关的层次模型和一种支持互联网及定位导航的定位服务体系结构，移动用户可以根据其当前的需要选择不同类型的位置数据输出。     

位置服务中对移动物体的时空索引*

在TPR*tree的基础上提出了DTPR*tree索引结构, 引进了事务时间和有效时间。它能索引移动物体过去、当前和未来的位置信息,支持基本位置查询和空间约束查询,有很好的空间、查询和更新效率。