  We study the ground state and low-energy excitations of fractional quantum
Hall systems on a disk at filling fraction $\nu = 5/2$, with Coulomb
interaction and background confining potential. We find the Moore-Read ground
state is stable within a finite but narrow window in parameter space. The
corresponding low-energy excitations contain a fermionic branch and a bosonic
branch, with widely different velocities. A short-range repulsive potential can
stabilize a charge $+e/4$ quasihole at the center, leading to a different edge
excitation spectrum due to the change of boundary conditions for Majorana
fermions, clearly indicating the non-Abelian nature of the quasihole.
