富铈混合稀土对AZ81合金组织与性能的影响

研究了富铈混合稀土对挤压铸造AZ81合金的显微组织和力学性能的影响。结果表明:加入不同含量富铈混合稀土的合金中都出现了一种新相Al11(Ce,La)3相,Al11(Ce,La)3相数量增多而Mg17Al12相则减少,能细化合金的组织晶粒,其细化作用在添加了1.5%富铈混合稀土的镁合金中尤为明显,但是当富铈混合稀土加入量大于2.0%时,合金中Al11(Ce,La)3相开始长大以粗大长杆状存在;在富铈混合稀土含量为1.5%时,AZ81合金的室温和150℃的综合力学性能达到最佳效果,超过2.0%时合金的室温和150℃综合力学性能开始下降;合金试样的拉伸断口带有局部韧窝的解理断裂和韧性断裂的混合特征。     

第12届亚洲物理奥林匹克竞赛实验题介绍与解答

介绍了第12届亚洲物理奥林匹克竞赛所考的"导体在振荡磁场中的悬浮"和"光学‘黑盒子'"2个独立实验的试题及竞赛组织者给出的标准解答.     

Pattern Formation in the Turing-Hopf Codimension-2 Phase Space in a Reaction-Diffusion System

We systematicaily investigate the behaviour of pattern formation in a reaction-diffusion system when the system is located near the Turing-Hopf codimension-2 point in phase space. The chloride-iodide-malonic acid （CIMA） reaction is used in this study. A phase diagram is obtained using the concentration of polyvinyl alcohol （PVA ） and malonic acid （MA） as control parameters. It is found that the Turing-Hopf mixed state appears only in a small vicinity near the codimension-2 point, and has the form of hexagonal pattern overlapped with anti-target wave; the boundary line separating the Taring state and the wave state is independent of the concentration of MA, only relies on the concentration of PVA. The corresponding numerical simulation using the Lengyel-Epstein （LE） model gives a similar phase diagram as the experiment; it reproduces most patterns observed in the experiment. However, the mixed state we obtain in simulation only appears in the anti-wave tip area, implying that the 3-D effect in the experiments may change the pattern forming behaviour in the codimension-2 regime.