[LONGITUDINAL]
input = {ka, Tk0, V, k}

EQUATION:
D  = 100

if t<Tk0
  f0=D/(V*Tk0*k)*(1-exp(-k*t))
else
  f0=D/(V*Tk0*k)*(1-exp(-k*Tk0))*exp(-k*(t-Tk0))
end

f1 = f0
f2 = D*ka/(V*(ka-k))*(exp(-k*t) - exp(-ka*t))
