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

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

Autodifférenciation et induction de cartilage à partir de mésenchyme somitique de Poulet cultivé <i>in vitro</i>

ABSTRACT Self-differentiation and induction of cartilage from chick somitic mesenchyme cultured in vitro It has been shown (Strudel &amp; Watterson) that in the absence of inductors (neural tube and notochord) the somitic mesenchyme of the chick embryo does not differentiate in situ into cartilage until after the 27-30 somite stage. In culture, in a medium based upon embryo extract (diluted or undiluted), cartilage only differentiates in mesenchyme taken from embryos of 27 somites. If, on the other hand, the mesenchyme is wrapped in vitelline membrane and cultured in a medium containing undiluted embryo extract it self-differentiates from the 17-somite stage. Differentiation into cartilage can be obtained in mesenchyme taken from younger embryos if extracts of inductors—neural tube and notochord—are added to the culture medium. In these circumstances chondrogenesis may occur in mesenchyme from an embryo of 20 somites when the embryo extract is diluted or from an embryo of 13 somites if it is not. If the somitic mesenchyme from 8 somite embryos is both wrapped in vitelline membrane and cultured in a medium based upon undiluted embryo extract then differentiation of cartilage occurs. These results show that the time-relations of chondrogenesis from chick somitic mesenchyme cultured in vitro varies with the composition of the medium and with the method of culture. These variations make it clear that the capacity of somitic mesenchyme to differentiate into cartilage may exist at very early stages. This early capacity is not revealed unless the somitic mesenchyme is cultured in a very favourable nutritive medium and in the presence of extracts of inducing tissues.</jats:p