Electronic shell effects and the stability of alkali nanowires
  Experimental conductance histograms for Na nanowires are analyzed in detail and compared to recent theoretical results on the stability of cylindrical and elliptical nanowires, using the free-electron model. We find a one-to-one correspondence between the peaks in the histograms and the most stable nanowire geometries, indicating that several of the commonly observed nanowires have elliptical cross sections. 
D. F. Urban, J. B\"urki, A. I. Yanson, I. K. Yanson, C. A. Stafford,   J. M. van Ruitenbeek, Hermann Grabert