On Groups with Two Isomorphism Classes of Derived Subgroups

The structure of groups which have at most two isomorphism classes of derived subgroups (D-2-groups) is investigated. A complete description of D-2-groups is obtained in the case where the derived subgroup is finite: the solution leads an interesting number theoretic problem. In addition, detailed information is obtained about soluble D-2-groups, especially those with finite rank, where algebraic number fields play an important role. Also, detailed structural information about insoluble D-2-groups is found, and the locally free D-2-groups are characterized.

A microstructure based model of the deformation mechanisms and flow stress during elevated temperature straining of a magnesium alloy

We show that the variation of flow stress with strain rate and grain size in a magnesium alloy deformed at a constant strain rate and 450 °C can be predicted by a crystal plasticity model that includes grain boundary sliding and diffusion. The model predicts the grain size dependence of the critical strain rate that will cause a transition in deformation mechanism from dislocation creep to grain boundary sliding, and yields estimates for grain boundary fluidity and diffusivity.