The 4-panel layout contains two nanotube models and two molecular structure sketches. S W C N T is a single cylindrical nanotube with a hexagonal lattice wall. M W C N T is a nested nanotube structure with multiple cylindrical lattice layers. S i O sub 2 is represented as connected ring-like units made of circular nodes. T i O sub 2 is represented as an oval boundary containing many narrow vertical oval shapes.