Cohesive zone models provide an illuminating and tractable way to include constitutive nonlinearity into continuum models of defects. Powerful insights have been gained by studying both dislocations and cracks using such analyses. Recent work has shown that as a result of the locality assumption present in such cohesive zone models, significant errors can be made in the treatment of defect ener...

We have performed density functional calculations on solids in four columns of the periodic table, containing the elements Ca, Sr, Ba, As, Sb, Bi, Cu, Ag, Au, Ce, and Th. In order to get a meaningful estimation of the quality of the generalized gradient approximation ~GGA! to predict trends within a column, as few other approximations were made as possible. Most notably, the spin-orbit effect h...

When using quantum chemistry techniques to calculate the energetics of bulk crystals, there is a need to calculate the Hartree-Fock (HF) energy of the crystal at the basis-set limit. We describe a strategy for achieving this, which exploits the fact that the HF energy of crystals can now be calculated using pseudopotentials and plane-wave basis sets, an approach that permits basis-set convergen...

We present a new approach to theory revision that uses a linguistically based semantics to help detect and correct errors in classification rules. The idea is that preferring linguistically cohesive revisions will enhance the comprehensibility and ultimately the accuracy of rules. We explain how to associate terms in the rules with elements in a lexical class hierarchy and use distance within t...

We study some generalized notions of cohesiveness which arise naturally in connection with eeective versions of Ram-sey's Theorem. An innnite set A of natural numbers is n{cohesive (respectively, n{r{cohesive) if A is almost homogeneous for every computably enumerable (respectively, computable) 2{coloring of the n{element sets of natural numbers. (Thus the 1{cohesive and 1{r{cohesive sets coinc...