Usachev, A. D., Zobnin, A. V., Petrov, O. F., Fortov, V. E., Annaratone, B. M., Thoma, M. H., et al. (2009). Formation of a boundary-free dust cluster in a low-pressure gas-discharge plasma. Physical Review Letters, 102(4): 045001. doi:10.1103/PhysRevLett.102.045001.