On the core structure and mobility of the 〈100〉{010} and 〈100〉{01^-1} dislocations in B2 structure YAg and YCu

Dislocations are thought to be the principal mechanism of high ductility of the novel B2 structure intermetallic compounds YAg and YCu.In this paper,the edge dislocation core structures of two primary slip systems 〈100 〉{010} and 〈100 〉 {011} for YAg and YCu are presented theoretically within the lattice theory of dislocation.The governing dislocation equation is a nonlinear integro-differential equation and the variational method is applied to solve the equation.Peierls stresses for 〈100 〉 {010} and 〈100 〉 {011} slip systems are calculated taking into consideration the contribution of the elastic strain energy.The core width and Peierls stress of a typical transition-metal aluminide NiAl is also reported for the purpose of verification and comparison.The Peierls stress of NiAl obtained here is in agreement with numerical results,which verifies the correctness of the results obtained for YAg and YCu.Peierls stresses of the 〈100 〉 {011} slip system are smaller than those of〈100 〉 {010} for the same intermetallic compounds originating from the smaller unstable stacking fault energy.The obvious high unstable stacking fault energy of NiAl results in a larger Peierls stress than those of YAg and YCu although they have the same B2 structure.The results show that the core structure and Peierls stress depend monotonically on the unstable stacking fault energy.     

锯齿型单壁碳纳米管的广义层错能计算

基于密度泛函理论的第一性原理方法，计算了两种不同半径的锯齿型单壁碳纳米管以及单层石墨的广义层错能曲线。对小位移处广义层错能曲线进行斜率拟合所得切变模量与其它文献值一致。对三条广义层错能曲线的对比可知，锯齿型碳纳米管与单层石墨的广义层错能曲线相近，锯齿型单壁碳纳米管的曲率效应不明显。     

溶胶陈化对聚酰亚胺/二氧化硅杂化薄膜性能的影响

采用不同陈化时间的酸催化硅溶胶制备SiO2含量一定的聚酰亚胺/二氧化硅杂化薄膜,用FTIR-ATR、SEM、TMA等手段对其微相结构、热稳定性、力学性能进行了研究.结果表明:随着硅溶胶水解和聚合反应的进行,杂化薄膜中的SiO2颗粒由棒状长大为球体,并逐渐团聚、变形,薄膜的光学透明性降低,热膨胀系数逐渐减小,拉伸强度先增大后减小.当球形SiO2颗粒的直径小于1 μm且均匀分布在基体中时,薄膜综合性能最优.     

Dislocation energy and calculation from Peierls stress： a rigorous the lattice theory

In the classical Peierls-Nabarro （P-N） theory of dislocation, there is a long-standing contradiction that the stable configuration of dislocation has maximum energy rather than minimum energy. In this paper, the dislocation energy is calculated rigorously in the context of the full lattice theory. It is found that besides the misfit energy considered in the classical P-N theory, there is an extra elastic strain energy that is also associated with the discreteness of lattice. The contradiction can be automatically removed provided that the elastic strain energy associated with the discreteness is taken into account. This elastic strain energy is very important because its magnitude is larger than the misfit energy, its sign is opposite to the misfit energy. Since the elastic strain energy and misfit energy associated with discreteness cancel each other, and the width of dislocation becomes wide in the lattice theory, the Peierls energy, which measures the height of the effective potential barrier, becomes much smaller than that given in the classical P-N theory. The results calculated here agree with experimental data. Furthermore, based on the results obtained, a useful formula of the Peierls stress is proposed to fully include the discreteness effects.     

From Discreteness to Continuity： Dislocation Equation for Two-Dimensional Triangular Lattice

A systematic method from the discreteness to the continuity is presented for the dislocation equation of the triangular lattice. A modification of the Peierls equation has been derived strictly. The modified equation includes the higher order corrections of the discrete effect which are important for the core structure of dislocation. It is observed that the modified equation possesses a universal form which is model-independent except the factors. The factors, which depend on the detail of the model, are related to the derivatives of the kernel at its zero point in the wave-vector space. The results open a way to deal with the complicated models because what one needs to do is to investigate the behaviour near the zero point of the kernel in the wave-vector space instead of calculating the kernel completely.     

电荷屏蔽对快中子俘获过程的影响

本文计算在初生中子星中微子驱动的星风环境中弱电荷屏蔽对质子电子俘获反应的影响.结果表明电荷屏蔽对星风中核子的比加热率、熵等物理参量基本没有影响.但是可以明显提高电子丰度,而这种提高有力地支持了最新的快中子俘获核合成结果.     

肥皂泡筏中的力律与肥皂泡半径的关系

利用肥皂泡之间的吸引排斥相互作用和Peierls切割粘合方案研究了不同半径泡筏边界上的肥皂泡所受的回复力与位移的关系曲线.计算得到回复力达到最大值的位置与Bragg所获得的结果一致，结合曲线的物理特征，给出一个新的函数形式来描述此力律曲线，从而得到肥皂泡筏中的力律与肥皂泡半径的关系. 关键词： 位错方程 力律 肥皂泡筏     

导弹武器系统费用的模糊估算模型研究

利用模糊数学的基本原理,基于模糊贴近度的概念和择近原则,在同一条件下,研究和对比在研导弹武器系统与已有导弹武器系统的相似程度,在导弹武器系统费用历史资料的基础上,根据指数平滑法的理论,建立了在早期设计阶段导弹武器系统费用的模糊预测模型。仿真实例验证了该方法的适用性和结果的可靠性。     

An improvement of the lattice theory of dislocation for a two-dimensional triangular crystal

The structure of dislocation in a two-dimensional triangular crystal has been studied theoretically on the basis of atomic interaction and lattice statics. The theory presented in this paper is an improvement to that published previously.Within a reasonable interaction approximation, a new dislocation equation is obtained, which remedies a fault existing in the lattice theory of dislocation. A better simplification of non-diagonal terms of the kernel is given. The solution of the new dislocation equation asymptotically becomes the same as that obtained in the elastic theory, and agrees with experimental data. It is found that the solution is formally identical with that proposed phenomenologically by Foreman et al, where the parameter can be chosen freely, but cannot uniquely determined from theory. Indeed, if the parameter in the expression of the solution is selected suitably, the expression can be well applied to describe the fine structure of the dislocation.     

EXCHANGE COUPLING BETWEEN TWO MAGNETIZED LAYERS IN A METAL

The exchange coupling energy for two magnetized monolayers embedded symmetrically in a metal and polarized in an arbitrary direction has been investigated in contact interaction approximation. Since the model can be solved exactly in particular for free-electron case, the coupling energy contributed from both extended state electrons and bound state electrons is calculated rigorously. For weak interaction, it is found that the leading term in the power-series expansion of density of states can give a correct coupling energy compared with rigorous one while extended state electrons give a much larger coupling energy. Furthermore, the relevant problems such as phase shift, 90°coupling and lattice effects have been discussed; an asymptotic expression of the interlayer coupling has been derived in a different way and used to calculate the exchange energy between magnetic layers in copper with Fermi surface obtained from de Haas-van Alphen effect.