In the work of H B Nielsen and P Olesen in 1973 "Vortex-line models for dual strings," Nuclear Physics B 61-45–61, they mentioned that
>"The many good experimental and theoretical features of the Veneziano model seem to suggest that an underlying string structure [1-4] of hadronic matter is a likely possibility."
as well as
> "It is the purpose of the present article to point out that it is easy to build up classical field theories allowing for vortex lines (or similar string-like structures) with the property of having equations of motion identical with those of the Nambu dual string ."
Since the Refs [1-2] are mostly in the format of the Conference reports, as follows,
 Y. Nambu, Prec. Int. Conf. on symmetries and quark models, (Wayne State University, 1969);
H.B. Nielsen, 15th Int. Conf. on high energy physics, Kiev, 1970;
L. Sussldnd, Nuovo Cimento 69A (1970) 457.
 Y. Nambu, Lectures at the Copenhagen Summer Symposium, 1970.
I was wondering whether there are following up papers or published lecture notes on these Refs [1-2] in the literature?
Thanks in advance.