Tilly works to swap the particle matrix and the emitter aboard Discovery
The particle matrix was a component on Starfleet vessels whose function fed into the shields.
At Starfleet Academy in the 2250s, Sylvia Tilly (as part of a drinking game) successfully swapped a particle matrix and emitter while blindfolded. She later used this skill in combat aboard the USS Discovery, during the Battle near Xahea in 2257. From a Jefferies tube in zone 4, she was successfully able to restore shield strength to 40%. (DIS: "Such Sweet Sorrow, Part 2")