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2. R. Zoelly, Ueber ein Knickungsproblem an der Kugelschale, Ph.D. Thesis, Eidgenössische Technische Hochschule Zürich (1915).
3. A. Van der Neut, De elastische Stabiliteit van den dunwandigen Bol, Ph.D. Thesis, Delft University of Technology (1932).
4. Imperfection sensitivity of externally pressurized spherical shells;Hutchinson;J. Appl. Mech.,1967
5. The axisymmetric buckling of initially imperfect complete spherical shells;Koga;Int. J. Solids Struct.,1969