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см. тж. внешняя граница; на границе фаз; на границах зёрен

We should establish a strict line of demarcation (or dividing line) between mechanics' work and the work of mechanics' helpers.

The dashed line indicates the demarcation (or boundary) between these two regions.

Источник: Русско-английский научно-технический словарь на Gufo.me