"critical regions" is a correct phrase and can be used in written English.
Example: The researchers identified several critical regions in the brain that are responsible for decision making.
Few, for instance, are found near the critical regions known as homeobox gene clusters.
A global monitoring system has been built that can detect an explosion as small as one-tenth of a kiloton, and 10 times smaller in many critical regions.
In half a dozen critical regions, Crumpton has organized meetings among American diplomats, intelligence officials, and combat commanders, so that information about cross-border terrorist threats is shared.
One approach of the improvement is to refine the discretization near the critical regions.
This technique leads to more reliable results because the mesh is denser in the critical regions.
We construct two critical regions as shown in Figure 2, according to their joint distribution.
Cf. Malinas 1997, 349 350 (note 3), where critical regions for the data are also provided.
The three critical regions for enzyme activity showed ds/dn ratio >1.
The zones near to these notches become critical regions under various working loading.
This suggests improvements in the design provisions, particularly those related to beam critical regions.
Longitudinal butt welded joints are critical regions as they are loaded transversely.
