It has come to our attention that Eq. 16 in our paper is incorrectly listed as identical to Eq. (13). With the thought that it is never too late to get it right, and there is always time for one last proofreading, Eq. 16 of Johnson and Tarbell [1] should read
$k1,k2=Mα2±M2α24+(β11β22+Mα)$
16