TB
Here is a serious answer, honest.
They are called thrust attenuators and are moved into the exhaust to deflect the thrust at idle (tickover), this reduces forward thrust while you are trying to slow down. Idle rpm's are fairly high and there is quite a lot of residual thrust.
The CJ3 does not have them as the engines are FADEC controlled and idle at a lower rpm, therefore less residual thrust.
They are operated by levers on the throttle quadrant, and are not interconnected to N1 values.
Cheers,
f