798 research outputs found
Suggestions for a non-monotonic feature logic
We use Scott's domain theory and methods from Reiter's default logic to suggest some ways of modelling default constraints in feature logic. We show how default feature rules, derived from default constraints, can be used to give ways to augment strict feature structures with default information
Mechanizing the metatheory of sledgehammer
This paper presents an Isabelle/HOL formalization of recent research in automated reasoning: efficient encodings of sorts in unsorted first-order logic, as implemented in Isabelle’s Sledgehammer proof tool. The formalization provides the general-purpose machinery to reason about formulas and models, emulating the theory of institutions. Quantifiers are represented using a nominal-like approach designed for interpreting syntax in semantic domains
Towards a first principles description of phonons in NiPt disordered alloys: the role of relaxation
Using a combination of density-functional perturbation theory and the
itinerant coherent potential approximation, we study the effects of atomic
relaxation on the inelastic incoherent neutron scattering cross sections of
disordered NiPt alloys. We build on previous work, where
empirical force constants were adjusted {\it ad hoc} to agree with experiment.
After first relaxing all structural parameters within the local-density
approximation for ordered NiPt compounds, density-functional perturbation
theory is then used to compute phonon spectra, densities of states, and the
force constants. The resulting nearest-neighbor force constants are first
compared to those of other ordered structures of different stoichiometry, and
then used to generate the inelastic scattering cross sections within the
itinerant coherent potential approximation. We find that structural relaxation
substantially affects the computed force constants and resulting inelastic
cross sections, and that the effect is much more pronounced in random alloys
than in ordered alloys.Comment: 8 pages, 3 eps figures, uses revtex
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