电脑未来“命系”围棋

在电影《美丽心灵》的开头,有这样一个镜头——数学家约翰·纳什坐在普林斯顿大学的校园里,俯身对着一个棋盘冥思苦想,棋盘上分布着一些看上去像卵石的黑白小棋子。在“围棋”这种古老的亚洲游戏中的挫折促使纳什探究这个游戏的数理机制。

Deformation behavior and processing maps of Mg-Zn-Y alloy containing Ⅰ phase at elevated temperatures

The microstructure and mechanical properties of extruded Mg-Zn alloy containing Y element were investigated in temperature range of 300-450°C and strain rate range of 0.001-1 s-1 through hot compression tests.Processing maps were used to indicate optimum conditions and instability zones for hot deformation of alloys.For Mg-Zn and Mg-Zn-Y alloys,peak stress,temperature and strain rate were related by hyperbolic sine function,and activation energies were obtained to be 177 and 236 kJ/mol,respectively.Flow curves showed that the addition of Y element led to increase in peak stress and decrease in peak strain,and indicated that DRX started at lower strains in Mg-Zn-Y alloy than in Mg-Zn alloy.The stability domains of Mg-Zn-Y alloy were indicated in two domains as 1)300°C,0.001 s-1;350°C,0.01-0.1 s-1 and 400°C,0.01 s-1 and 2)450°C,0.01-0.1 s-1.Microstructural observations showed that DRX was the main restoration mechanism for alloys,and fully dynamic recrystallization of Mg-Zn-Y alloy was observed at 450°C.The instability domain in Mg-Zn-Y alloy was located significantly at high strain rates.In addition,the instability zone width of Mg-Zn and Mg-Zn-Y alloys increased with increasing strain,and cracks,twins and severe deformation were considered in these regions.

A novel method to improve interfacial bonding of compound squeeze cast Al/Al-Cu macrocomposite bimetals:Simulation and experimental studies

A facile and innovative method to improve bonding between the two parts of compound squeeze cast Al/Al-4.5 wt.%Cu macrocomposite bimetals was developed and its effects on microstructure and mechanical properties of the bimetal were investigated.A special concentric groove pattern was machined on the top surface of the insert(squeeze cast Al-4.5 wt.%Cu) and its effects on heat transfer,solidification and distribution of generated stresses along the interface region of the bimetal components were simulated using ProCAST and ANSYS softwares and experimentally verified. Simulation results indicated complete melting of the tips of the surface grooves and local generation of large stress gradient fields along the interface. These are believed to result in rupture of the insert interfacial aluminum oxide layer facilitating diffusion bonding of the bimetal components. Microstructural evaluations confirmed formation of an evident transition zone along the interface region of the bimetal. Average thickness of the transition zone and tensile strength of the bimetal were significantly increased to about 375 μm and 54 MPa, respectively, by applying the surface pattern.The proposed method is an affordable and promising approach for compound squeeze casting of Al-Al macrocomposite bimetals without resort to any prior cost and time intensive chemical or coating treatments of the solid insert.

Graphic Organizers and Reading Comprehension Ability： Evidence From Iranian EFL University Students

The present study investigated the impact from GOs （Graphic Organizers） upon reading comprehension ability. To this end, an OPT （Oxford Placement Test） was administered to a research population （N = 354） in order to homogenize it. On the basis of the test results, the population was sorted into three groups of reading-low, reading-mid, and reading-high students. Sixty participants with the lowest level of reading comprehension proficiency were randomly selected and assigned to an EG （Experimental Group） （N = 30） and a CG （Control Group） （N = 30）. Afterwards, a TOEFL （Test of English as a Foreign Language） reading comprehension pretest was administered to both groups in order to determine their current level of reading proficiency. Then, the EG received 10 successive 90-minute sessions on GOs as post-reading strategies for expository text comprehension, while the CG received the same amount of treatment on other post-reading strategies. In the end, another TOEFL reading comprehension posttest was administered to the research groups to measure their reading comprehension performance level after the treatment. The results revealed that GOs were statistically more significant and effective for the low-skilled readers than other post-reading strategies.