Why that is so lies buried in the different crystalline structures of the two materials.

ECONOMIST: Aircraft fatigue

There need to be two separate support structures for these two types (SME and IDE) that have different support personnel and different programs.

FORBES: Drawing The Line: Why Startups Are 'Sexy' And Small Businesses 'Meh'

And even though the two agencies would regulate similar types of products, their structures are entirely different.

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The two regions of the world of most interest to military planners are quite dissimilar and really require different force structures.

CENTERFORSECURITYPOLICY: Section IV: Building a Two-MRC Force for the 21st Century