A fluid bed reactor contains catalyst particles with a mean diameter of $500 \mu \mathrm{m}$ and a density of $2.5 \mathrm{~g} / \mathrm{cm}^{3}$. The reactor feed has properties equivalent to $35^{\circ} \mathrm{API}$ distillate at $400^{\circ} \mathrm{F}$. Determine the range of superficial velocities over which the bed will be in a fluidized state.