The first and second derivative plates of concave pressure build - up curve are presented in this paper.

本文提出了凹型压力恢复曲线的一阶导数图版和二阶导数图版.

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Traditionally, the method of bar code recognition is based on zero crossing of the second derivative.

传统的条码识别方法是通过二阶导数零交叉来定位条码边界.

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