Some remarks on the internal symmetries of relativistic wave equationsLoide, Rein-KarlActa physica Polonica. B, Particle physics and field theory, nuclear physics, theory of relativity1983 / p. 671-678 https://www.ester.ee/record=b3360521*est

Three-dimensional shell-theory of axially symmetric transient wave in a semi-infinite cylindrical shellNigul, UnoArchives of mechanics = Archiwum mechaniki stosowanej1967 / p. 839-856 https://www.ester.ee/record=b1848871*est