In our recent study, we put an experimental-like initial dislocation structures cut from larger deformed samples into 3D DDS, which is much more realistic than in similar studies, and found the scarcity of available dislocation sources is a major contribution to the higher flow stress and larger scatter of strength in smaller sizes. In addition, some importance features about dynamic behavior of dislocations in small volumes have been captured in our simulations.  Please see the link:

http://www.sciencedirect.com/science/article/pii/S1359645409007678