Abstract :
It is pointed out that the spherical symmetric diffusion equation of fractional order
for the time, recently proposed by E.Roman and Giona [J.Phys.A2 5(1992)2107-21171:
dt l’d”P(r,t) = -A
corresponds, for integer spatial dimensions d = 1 and d = 3, to the long time description of a the
fractal-time continuous-time random- walk, in which the interjump density has the asymptotic
form Q(t) -t-i--?, with 0 < 7 = 2/d, < 1.
