Lelyakov, O.P., Karpenko, A.S. and Babadzhan, R.-D.O. 2018. Dynamics of a Non-Rotating Test Null String in the Gravitational Field of a Closed “Thick” Null String Radially Expanding or Collapsing in the Plane z = 0. Ukrainian Journal of Physics. 59, 11 (Oct. 2018), 1114. DOI:https://doi.org/10.15407/ujpe59.11.1114.