Submitted on: 16 October 2001.
Revised on: 26 November 2001.
Accepted on: 06 January 2002.
___________________Journal of Theoretical and Applied Mechanics-Bulgaria
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Submitted on: 31 January 2018.
Revised on: 19 March 2018.
Accepted on: 08 April 2018.
___________________Journal of Theoretical and Applied Mechanics-Bulgaria
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Submitted on: 07 February 2004.
Revised on: 04 May 2004.
Accepted on: 21 June 2004.
___________________Journal of Theoretical and Applied Mechanics-Bulgaria
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Submitted on: 22 July 2020.
Revised on: 08 October 2020.
Accepted on: 31 October 2020.
___________________Journal of Theoretical and Applied Mechanics-Bulgaria
Submitted on: 04 June 1999.
Revised on: 23 September 1999.
Accepted on: 09 October 1999.
___________________Journal of Theoretical and Applied Mechanics-Bulgaria
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