区间数据样本下指数分布平均寿命的矩估计

讨论了区间数据样本下单参数指数分布的两种矩估计问题.分别利用δi和(Vi,δi)构造出单参数指数分布的两种矩估计,就无偏性和渐近方差为指标,得到两种矩估计的比较.     

一种新的迭代方法

本文应用整函的理论及文献[2]的基本定理,推导出了一种求解方程F(z)=0近似解的新迭代方法,分别得出了当F(z)是亚纯函数、整函数、实函数时的迭代公式,指出这种新的迭代方法包括了牛顿迭代法,并用实例说明了应用这种新的迭代方法求方程的近似解,比应用熟知的牛顿法、迭代法计算简便,收敛较快。     

一类二阶非线性微分方程解的渐近性态

在一定条件下，研究了一类二阶非线性微分方程的解的渐近性态，并研究了其解的单调性和可延拓性条件以及其解有界的充分必要条件，得到了这类介非线性微分方程的解与二阶线性微分方程的解的渐近关系，以及这两个方程的某些解的等价性条件。     

Creep behavior and effect factors of a TiAl–Nb alloy at high temperature

The effect of solution treatment on the microstructure and creep properties of forged TiAl–Nb alloys was investigated. The results showed that the microstructure of forged alloy mainly consisted of γ/α₂ lamellar colonies and fine equiaxed recrystallized γ/α₂ grains. During the solution treatment the microstructure of the alloy transformed into a fully lamellar structure due to the lamellar colonies growth by consuming equiaxed grains. Compared with the forged alloy the creep life of the solution treated alloy at 800 ?°C/220 ?MPa increased from 116 ?h to 339 ?h. The better creep resistance may be attributed to the transform of fine equiaxed γ/α₂ grain to the lamellar colonies with serrated grain boundaries due to the solution treatment. The deformation mechanism of the solution treated alloy during creep is considered to be dislocation slipping within the lamellar γ/α₂ phases, and the dislocation movement may be hindered by the γ/α₂ interface and the formation of dislocation tangles. The interaction of the dislocations with the tangles may increase the resistance of the dislocation motion and hence improve the creep resistance of the alloy. It was found that during the creep of the forged alloys the cracks mainly initiated at the equiaxed grain, and in the solution treated alloy the cracks initiated at the grain boundaries. As creep continued the cracks propagated and connected to each other, leading to the damage and rupture of the forged and solution treated alloys.     

部分线性变系数EV模型估计的渐近正态性

研究非参数部分带有测量误差(EV)的部分线性变系数模型,综合局部纠偏方法和Profile最小二乘估计方法定义了模型中未知参数和系数函数的估计,并在适当条件下证明了它们的渐近性质,最后通过数值模拟研究了所提估计方法在有限样本下的实际表现。     

弦振动方程中D＇Alembert公式的算子算法

主要讨论了运用算子的方法推导出弦振动方程中的D＇Alembert公式．弦振动方程中的D＇Alembert公式是偏微分方程中一个非常重要的基本公式．该公式的推导方法中一个最基本方法是特征线法．本文从另一角度即算子的方法，将弦振动方程写成算子的形式，再根据一阶线性偏微分方程的求解方法，最终推导出D＇Alembert公式．     

我国农业适度规模经营面临的难题

本文认为要实现农业的适度规模经营,要解决的问题很多,而其中农民对土地根深蒂固的依赖观念,比较效益和农村剩余劳动力的就业问题是最需解决好的,观念问题可通过比较效益来解决,比较效益的实现又依赖于让出土地的农民能找到就业门路来解决,归结到农村劳动力的出路,其解决的难度特别大,因此,解决农村剩余劳动力的出路问题便应格外引起重视。