Processing and Ductile-Brittle Transitions in PM Manganese Steels

YesBrittleness in manganese steels can be associated with processing in a "wet¿ [micro]climate resulting in the formation of continuous oxide networks. The formation of these networks can be prevented by sintering in an atmosphere, also ¿local¿ in a semiclosed container, adhering to the Ellingham-Richardson oxide reduction criteria. When this requirement is satisfied, however, further types of ductile ¿ brittle transitions are observed. Rapid cooling, typically above 40°C/min, produces enough martensite to render Fe-(3-4)Mn-(0·6-0·7)C material macroscopically brittle. Quenched and conventionally tempered structures remain brittle. It is tentatively suggested that segregation of minor alloying/tramp element(s), as in cast materials, is responsible for this temper embrittlement. To overcome it, heat treatment at a temperature no higher than 200°C, recovery/stress relief, is recommended

The Role of Company Stock in Defined Contribution Plans

This paper explores the risks and benefits of holding company stock in employer-sponsored defined contribution (DC) retirement plans. We address three questions: (1) What is the role and function of company stock in such plans? (2) Who might be affected by enhanced portfolio diversification in such plans? and (3) What mechanisms exist, or might be developed, to enhance portfolio diversification if more diversification were deemed useful? Firms offer company stock within DC plans in an effort to enhance economic performance, though evidence is mixed on productivity gains from stock ownership. We demonstrate that concentrated stock positions arise most often in larger firms' DC plans where sponsors direct employer contributions and restrict diversification. Stock concentration also arises because participants systematically underestimate the risk of employer stock and over-rely on its past performance in making investment decisions. In a retirement system with concentrated stock positions, there will always be some participants who forfeit DC plan savings to firm bankruptcy. Encouraging plan diversification mitigates this risk, but it could also induce some companies to redirect plan contributions to other forms of stock compensation or to replace stock contributions with cash compensation. We conclude by describing policy tools that might be used to encourage diversification and discuss conditions for their effective implementation.

The Catalan simplicial set

The Catalan numbers are well-known to be the answer to many different counting problems, and so there are many different families of sets whose cardinalities are the Catalan numbers. We show how such a family can be given the structure of a simplicial set. We show how the low-dimensional parts of this simplicial set classify, in a precise sense, the structures of monoid and of monoidal category. This involves aspects of combinatorics, algebraic topology, quantum groups, logic, and category theory.Comment: 15 pages. Replaces and expands upon parts of arXiv:1307.0265; remaining parts of arXiv:1307.0265 will be incorporated into a sequel. Version 2: minor revision; to appear in Math. Proc. Camb. Phil. So

Duality between atomic configurations and Bloch states in twistronic materials

The relative orientation (twist) of successive layers of stacked two-dimensional (2D) materials creates variations in the interlayer atomic registry. The variations often form a super lattice, called a moir\'e pattern, which can alter electronic properties. In this work we introduce a classification of the single-particle electronic structures that can occur in twisted stacks of 2D layers by characterizing them as "moir\'e molecules" or "moir\'e crystals". The molecules generate localized electronic states and moir\'e flat bands, while the crystals are sometimes unconventional and produce electronic banding in the configuration basis. The underpinning of this classification is the duality between interlayer configuration and monolayer Bloch momentum in moir\'e Hamiltonians. We apply this understanding to diagrams of local electron density in untwisted geometries to produce intuitive and quantitative predictions of twistronic properties. We provide a conceptual introduction to this framework through a one-dimensional model, and then apply it to 2D twisted bilayers of the semi-metal graphene, and of MoS$_2$, a representative material of the transition metal dichalcogenide (TMDC) family of semiconductors. This level of thorough understanding of twistronic phenomena is vital in the search for new material platforms for localized moir\'e electrons.Comment: 13 pages, 9 figure

Reconstructing Old Norse oral tradition

The written residue of oral tradition from the medieval Nordic world encompasses a wide variety of pan-national genres, including charms, legends, and genealogical lore, but modern scholarly attention has generally focused on two areas: (1) the prose (and often prosimetrical) Icelandic sagas and (2) traditional poetry in its two dominant forms, eddic and scaldic.Not