some existent problems 其中存在的一些问题
From studying some kind of quite complex variational equation problems and applying the conclusion, we prove that the optimal control of new model is existent and characterize its structure.
通过对一类相当复杂的变分方程问题的研究并利用其有关结论，我们证明了新模型最佳控制的存在性并刻划出其结构。
The principal, component and performance of this kind of sensors are demonstrated, also some existent problems and the research direction in future are discussed.
对其原理、组成和性能进行了评述，并讨论了一些存在的问题和今后的研究方向。
Some existent problems about construction management of concrete in winter are explored in this paper.
探讨了冬期混凝土施工管理所存在的问题，并提出相应的解决办法。
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