Torsional vibration of nano-cone based on nonlocal strain gradient elasticity theory Mohsen Mahdavi Adeli, Amin Hadi, Mohammad Hosseini and Hamid Haghshenas Gorgani Eur. Phys. J. Plus, 132 9 (2017) 393 Published online: 18 September 2017 DOI: 10.1140/epjp/i2017-11688-0