Core absent areas, such as HVAC, parking, fire marshal and safety inspections, safety drills, personnel issues, non-classroom student discipline, athletics, plumbing, landscaping, etc...
Core Absent: Services are offline. Reinforcement is the same as a structure with a core. Tethering, Repairing, and Refitting are disabled. A Reinforced structure is sometimes interesting.

The structure you see with Core Absent are Grandfathered structures where they existed before the need for cores. Those structures were allowed to exist as is until they get popped and...

As we can see from the illustration, And Core Absent has many fascinating aspects to explore.
Cores: Internal zone, "core", in muscle fiber. Reduced, absent, or abnormal in core. Oxidative enzyme activity. Mitochondria.
I can calcuate it by using couple mode theory by calucting E field for one (or another) core taking other core absent and calculating the overlapp integral.