Lelyakov, O. P., A. S. Karpenko, and R.-D. O. Babadzhan. 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 =”. Ukrainian Journal of Physics 59 (11):1114. https://doi.org/10.15407/ujpe59.11.1114.