(Color online) Patterns of PTWs interacting with an up-triangle defect with height ( H = 20 △ x ) and width ( H = 30 △ x ) at t = 300. The pacing frequencies are ω=0.81ω₀ in (a), ω=0.93ω₀ in (b), and ω=0.964ω₀ in (c), respectively. (d) The dependence of ω_min/ω₀ on the defect width L. The PWTs fuse after colliding with the defect when ω < ω min while they break as ω > ω min . The height of the triangle H is fixed to be H = 10 △ x . (e) The phase diagram in the H-L plane describes three dynamical regimes with ω=0.94ω₀. The square, triangle, and circle mean the states of fusion, breakup to “V” pattern, and two counter-rotating spirals, respectively.