Plastic deformations in crystal, polycrystal, and glass in binary mixtures under shear: Collective yielding

Using molecular dynamics simulation, we examine the dynamics of crystal, polycrystal, and glass in a Lennard-Jones binary mixture composed of small and large particles in two dimensions. The crossovers occur among these states as the composition c is varied at fixed size ratio. Shear is applied to a system of 9000 particles in contact with moving boundary layers composed of 1800 particles. The particle configurations are visualized with a sixfold orientation angle alpha_j(t) and a disorder variable D_j(t) defined for particle j, where the latter represents the deviation from hexagonal order. Fundamental plastic elements are classified into dislocation gliding and grain boundary sliding. At any c, large-scale yielding events occur on the acoustic time scale. Moreover, they multiply occur in narrow fragile areas, forming shear bands. The dynamics of plastic flow is highly hierarchical with a wide range of time scales for slow shearing. We also clarify the relationship between the shear stress averaged in the bulk region and the wall stress applied at the boundaries.Comment: 17 pages, 15 figures, to appear in Physical Review

Social media campaigning in Europe: Mapping the terrain

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The Classic: A Morphogenetic Matrix for Differentiation of Cartilage in Tissue Culture

This Classic Article is a reprint of the original work by Hiroshi Nogami and Marshall R. Urist, A Morphogenetic Matrix for Differentiation of Cartilage in Tissue Culture. An accompanying biographical sketch of Marshall R. Urist, MD is available at DOI 10.1007/s11999-009-1067-4; a second Classic Article is available at DOI 10.1007/s11999-009-1068-3; and a third Classic Article is available at DOI 10.1007/s11999-009-1070-9. The Classic Article is © 1970 by the Society for Experimental Biology and Medicine and is reprinted with permission from Nogami H, Urist MR. A morphogenetic matrix for differentiation of cartilage in tissue culture. Proc Soc Exp Biol Med. 1970;134;530–535