TASK DEFINITION: Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.
PROBLEM: a sandwich panel is a kind of composite material, which is usually made of two components: a small outside layer (which is the same on both sides), and an inside layer, which is used to get certain properties, for example insulation or fire resistance.

SOLUTION: sandwich panel

PROBLEM: zhejiangopterus is a pterosaur that was found in china.

SOLUTION: zhejiangopterus

PROBLEM: nightmare disorder, also known as "dream anxiety disorder", is a sleep disorder characterized by frequent nightmares.

SOLUTION:
nightmare disorder