A	drug surface area per volume unit sphere, 1/cm
Ao	initial drug surface area per volume unit sphere, 1/cm
C(r,t)	dissolved drug concentration, g/mL
Ca(r,t)	un-dissolved drug concentration, g/mL
Cao	initial un-dissolved drug concentration, g/mL
Cs	solubility of drug in matrix, g/mL
Ct	initial total drug concentration Ct = Cao + Cs, g/mL
D	diffusivity of drug in matrix, cm2/s
G	ratio of diffusion rate to dissolution rate kAoro2/D
K	ratio of drug solubility to initial total drug concentration Cs/Ct
k	dissolution rate constant, 1/(cm2·s)
n	shape factor of a drug particle
r	radial coordinate from the left of a sphere, cm
ro	radius of a sphere, cm
r*	moving front, cm
t	time, s
u	unit step function
Greek symbols
φ(η,τ)	dimensionless dissolved concentration C/Ct
ϕ(η,τ)	dimensionless un-dissolved concentration Ca/Ct
η	dimensionless radius r/ro
η*	dimensionless moving front η/ro
τ	dimensionless time Dt/$r_o^2$
τc	dimensionless critical time
τs	dimensionless starting time of constant release rate region