1. Associate Professor Machine Elements, Luleå University of Technology, Luleå 97187, Sweden e-mail:
2. Assistant Professor Mathematics, Luleå University of Technology, Luleå 97187, Sweden e-mail:
3. Professor Machine Elements, Luleå University of Technology, Luleå 97187, Sweden e-mail:
4. Professor Mathematics, Luleå University of Technology, Luleå 97187, Sweden e-mail: peter.wall@ltu.se