研究一类四阶微分方程解的存在性，利用上下解及单调迭代的方法，得出这类四阶方程的最大解和最小解的存在。
We obtain the existence of extremal solutions of the boundary value problem by using the method of lower and upper solutions coupled with monotone iterative technique.
该方法不用一般的变分原理，可适用任意变系数正定和非正定偏微分方程。利用这一方法得到一个新的八节点四边形平面应力单元。
It doesn't need the variational principle and can be applied to solve non-positive or positive definite partial differential equations with arbitrary variable coefficient.
微分散射截面的变化主要依赖于相对介电常数实部、虚部数值较大的一方，并且随粒子取向角的增大而增大。
The variation of DSCS depends on the larger part between real part and imaginary part of dielectric coefficient. The DSCS and azimuth angle are in proportional relation.
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