H. Woracek:
"Asymptotics of eigenvalues for a class of singular Krein strings";
Collectanea Mathematica, 66 (2015), 469 - 479.
http://dx.doi.org/10.1007/s13348-014-0110-2Electronic version of the publication:
http://publik.tuwien.ac.at/files/PubDat_244571.pdf