 Strength-gravity disruption transition

For $Q_D^{\ast }=Q_a{D}^{-a}+Q_b{D}^b$, $a,b>0$, differentiation gives the minimum at the displayed diameter. Equal strength and gravity contributions occur instead at $D_{\mathrm{eq}}=(Q_a/Q_b{)}^{1/(a+b)}=(b/a{)}^{1/(a+b)}{D}_w$. These two transition conventions coincide only for $a=b$.