高温变形过程中的动态再结晶类型识别

通过分析高温变形过程中伴随再结晶晶粒长大的内部位错密度变化,判别不同变形条件下动态再结晶过程的进行形式,研究动态再结晶形式对变形参数的依赖规律,发现：低温大应变速率下,高温变形过程中的再结晶形式以连续性动态再结晶为主;高温低应变速率下,以周期性动态再结晶为主.根据动态再结晶软化与加工硬化平衡,得到反映稳态流动时钛合金流动应力对变形参数的响应,建立具有实际物理意义描述钛合金稳态流动本构关系的Arrhenius型方程.通过热模拟压缩实验得到800~900℃,0.0005~10 s-1条件下的TC18钛合金高温变形流动应力应变曲线,验证动态再结晶形式的判据模型,并通过DMM耗散效率分布图分析模型的适用性.通过显微组织分析,研究不同变形参数下的高温变形过程中,不同动态再结晶形式对应的再结晶晶粒粗化/细化的特点.通过各变形条件下真应变？=0.8时的稳态应力验证得到的本构模型,并分析应变速率敏感系数的变化规律.     

Microstructure and texture evolution during warm compression of the magnesium alloy AZ31

The evolution of the microstructure and texture with strain during compression at 150℃of the magnesium alloy AZ31 has been investigated using the electron backscattered diffraction(EBSD)technique.The initial samples were chosen to have a strong basal plane texture with the crystal c-axes perpendicular to the compression direction.The EBSD data provide evidence concerning the relative activity of both{10-12}extension twinning and slip,and suggest that non-basalc+a slip is important in samples deformed to a strain of more than 0.2.The relative contributions of the twinning and the slip during deformation have been discussed based on the results above.     

Recycling of magnesium drive train components

With the development of new heat resistant magnesium alloys,the automotive industry has introduced several parts to the drive train.The rising number of large magnesium components will result in a higher quantity of automotive post consumer scrap.It was the aim of this work to find a reasonable alloy system for the recycling of these magnesium drive train components.A matrix of potential recycling alloys based on the magnesium alloy AM50 was prepared via permanent mould casting.The materials were investigat...     

镁合金及其成形技术的国内外动态与发展

介绍了镁合金开发研究的国内外发展动态；综述了耐热镁合金、耐蚀镁合金、高强高韧镁合金、变形镁合金等高性能镁合金材料的最新发展，镁合金压铸、半固态铸造、挤压铸造、超塑性、冲锻等成形技术的最新开发研究成果。     

An improved neural network model for prediction of mechanical properties of magnesium alloys

An improved neural network model was developed for prediction of mechanical properties in the design and development of new types of magnesium alloys by refining the types of input variables and using a more reasonable algorithm.The results showed that the improved model apparently decreased the prediction errors,and raised the accuracy of the prediction results.Better preprocessing parameters were found to be[0.15,0.90]for the tensile strength,[0.1,0.9]for the yield strength,and[0.15,0.90]for the elongatio...     

Superplasticity of Mg-5.8Zn-1Y-Zr alloy sheet fabricated by combination of extrusion and hot-rolling processes

Superplastic behaviors of quasicrystal phase containing Mg-5.8Zn-1Y-0.48Zr alloy sheets fabricated by combination of extrusion and hot-rolling processes have been investigated at temperature ranging from 623 to 753 K and at the strain rates ranging from 10 -4 to 10 -2 s -1 by uniaxial tensile tests.An excellent superplasticity with the maximum elongation to failure of 1020%was obtained at 753 K and the strain rate of 1.04×10-3s -1and its strain rate sensitivity,m,is as high as up to 0.75. The microstructure was stable during superplastic deformation due to the uniformly distributed fine quasicrystal particles. In addition,micro-cavities and their coalescences were observed in the superplastic deformation of the ZW61 magnesium alloy.Grain boundary sliding(GBS)was considered to be the main deformation mechanism during the superplastic deformation.Dislocation creep controlled by atom diffusion through grain boundaries or interior grains is suggested mainly to accommodate the GBS in superplastic deformation.     

Anisotropic plastic deformation behavior of as-extruded ZK60 magnesium alloy at room temperature

The anisotropic plastic deformation behavior of as-extruded ZK60 magnesium alloy at room temperature(RT)was investigated by compressive and tensile testing in different directions,i.e.the loading axis oriented at 0°,45°and 90°to the extrusion direction.The relationship between texture and plastic deformation behavior were examined.The results show that the extruded ZK60 alloy exhibits a strong ring fiber texture.The mechanical properties are strongly orientation dependent.In tension testing,the 0°specimen exhibited higher yield strength and lower elongation.In compression testing,however,ZK60 alloy exhibited almost the same yield strength in three directions.The anisotropic plastic deformation behavior is due to strong fiber texture and the lower symmetry of the hexagonal close packed(hcp)structure of ZK60 alloy. The correlation between texture and mechanical behaviour offers the possibility to improve the mechanical properties of magnesium alloy by optimization of the material production process.     

Forecasting euro area inflation using dynamic factor measures of underlying inflation

Standard measures of prices are often contaminated by transitory shocks. This has prompted economists to suggest the use of measures of underlying inflation to formulate monetary policy and assist in forecasting observed inflation. Recent work has concentrated on modelling large data sets using factor models. In this paper we estimate factors from data sets of disaggregated price indices for European countries. We then assess the forecasting ability of these factor estimates against other measures of underlying inflation built from more traditional methods. The power to forecast headline inflation over horizons of 12 to 18 months is adopted as a valid criterion to assess forecasting. Empirical results for the five largest euro area countries, as well as for the euro area itself, are presented. Copyright © 2005 John Wiley & Sons, Ltd.     

梯级水电站群长期发电优化调度多核并行随机动态规划方法

随机动态规划求解水电站群长期发电优化调度易产生"维数灾"问题,导致计算耗时急剧增加,求解效率降低.如何缓解维数灾和提高计算效率,一直是水库优化调度致力于研究的难点问题.在随机动态规划的并行性分析基础上,提出了基于Fork/Join并行框架的多核并行随机动态规划方法.该方法将单个时段内所有变量组合状态下的计算任务作为父任务,通过分治法递归分解为多个子任务,并平均分配到不同的内核同时计算实现细粒度并行求解.以澜沧江下游梯级水电站群为研究实例,建立了3个变量离散数不同的调度方案,并在多核环境下验证该方法的计算效率.结果表明,在2和4核环境下,该方法的计算耗时与串行方法相比,分别节省了约50%和70%,大幅度缩减计算耗时,可充分利用多核资源;同时,计算任务的规模越大,并行计算的耗时缩减幅度越大.因此,此方法为大规模水电系统优化调度提供了一种可行途径,其并行原理可为其他应用所借鉴.     

列车通过大跨度桥梁桥塔区域过程中的风-车-桥耦合动力分析

大跨度桥梁位于强横风环境时,桥塔的遮挡作用会使列车进出桥塔区域时车体受到的风力发生变化,这种风荷载的突变效应会对车辆的动力响应造成影响,此外车辆动力响应的改变还会影响桥梁的动力响应.本文以瓯江大跨公铁两用悬索桥为工程背景,以快速谱分析模拟风场,对桥梁子系统施加抖振风力,对桥梁子系统施加稳态风力,考虑桥塔宽度与车辆长度的关系,建立风-车-桥耦合系统运动平衡方程,以全过程迭代法求解该方程,分析计算了不同车速与风速下桥塔遮风效应对车辆桥梁动力响应的影响.结果表明风速和桥塔宽度越大,车辆的动力响应越大,而桥梁动力响应受桥塔遮风效应影响很小.     

高速铁路基础结构动态性能演变及服役安全的基础科学问题

中国高速铁路已经由大规模建造进入长期安全稳定运营阶段,如何科学维护庞大规模的高速铁路运营线路,使高速铁路长期保持高安全、高稳定、高可靠的运营品质,是我国现阶段面临的重大课题.在分析总结中国高速铁路基础结构构造特点及其复杂运营环境特点的基础上,提出了高速铁路基础结构动态性能演变及服役安全的三个基础科学问题:环境与动载耦合重复作用下高速铁路基础结构关键工程材料与结构动态性能演变,高速铁路基础结构累积变形与轨面几何形态的映射关系,基础结构劣化与高速列车-基础结构耦合系统动态性能的相互影响及演化机制;回顾评述了国内外在此方面的研究现状与最新进展;指出了本领域今后的发展趋势以及需要重点关注和加强的基础研究工作.     

Regulation of caldesmon activity by Cdc2 kinase plays an important role in maintaining membrane cortex integrity during cell division

To study the mitosis-specific phosphorylation of caldesmon (CaD), we generated a mutant of the C-terminal fragment (amino acids 244–538) of human fibroblast CaD (CaD39-6F), as well as a mutant of the full-length CaD (CaD-6F), in which all six potential phosphorylation sites for Cdc2 kinase were abolished. The mitotic CaD39-6F-overexpressing cells required more time to progress from anaphase start to 50% cytokinesis, exhibited larger size, and abnormally formed numerous small blebs. In contrast, overexpression of the wild-type C-terminal fragment of CaD (CaD39) did not result in abnormal bleb formation, but led to larger size and prolonged the time requirement between anaphase start and 50% cytokinesis. Similar abnormal blebs were also observed in the CaD-6F-overexpressing cells. CaD-6F-overexpressing cells did not show larger size but required more time to progress from anaphase start to 50% cytokinesis. These results suggest that mitosis-specific phosphorylation of CaD plays a role in inhibiting bleb formation and that the N-terminal fragment of CaD is required for cell size determination. Received 4 September 2002; received after revision 25 November 2002; accepted 4 December 2002