Clare Martin

We introduce and study a natural extension of Marcus external contextual grammars. This mathematically simple mechanism which generates a proper subclass of simple matrix languages, known to be mildly context-sensitive ones, is still mildly context-sensitive. Furthermore, we get an infinite hierarchy of mildly context-sensitive families of languages. Then we attempt to fill a gap regarding the linguistic relevance of these mechanisms which consists in defining a tree structure on the strings generated by many-dimensional external contextual grammars, and investigate some related issues. Several open problems are finally discussed

Nowadays, the high-temperature plasticity of yttria-stabilized tetragonal zirconia polycrystals is successfully explained in terms of a threshold stress. Despite the fact that its existence is very well proved experimentally, the origin and nature of the threshold stress are still unexplained. This work develops a possible explanation for the threshold stress in YTZPs. The model developed in this paper is able to explain quantitatively the dependence of this threshold stress with temperature and grain size. The model is able to predict the influence of a glassy phase present at grain boundaries and the values of the threshold stress in YTZP nanocrystals. The theoretical results are discussed and compared with the available data in the literature