Then this paper studied the effect of diffusion coefficient on concentration distribution and the conditions of substitution with numerical dispersion for physical diffusion.

通过将该半解析解与忽略扩散的数值解进行对比分析，讨论了数值弥散代替物理扩散的条件。

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Destructive techniques are techniques in which the sample is decomposed by a reagent and then the concentration of the element in the aqueous extract determined by a physical technique.

破坏性技术是将样本溶解于溶剂，然后通过物理方法分析元素浓度的技术。

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When you observe your abdomen rise and fall, a physical process, and your concentration becomes deep enough, you begin to realize the rising and falling movements very clearly in their true nature.

当你观察腹部上下，即身体现象，并且当你的定力够深的时候，你就能清楚地看到上升和下降运动的真实本质。

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Physical activity encourages better concentration.

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Regular physical activity enhances important skills, like concentration and problem solving, which have been shown to improve academic performance.

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In addition, physically active kids do better in school, with studies showing that physical activity enhances important skills, like concentration and problem solving, which have been shown to improve academic performance.

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