The stability of the perfect screw dislocation in silicon has been investigated using both classical potentials and first-principles calculations. Although a recent study by Koizumi et al . stated that the stable screw dislocation was located in both the 'shuffle' and the 'glide' sets of {111} planes, it is shown that this result depends on the classical potential used, and that the most stable configuration belongs to the 'shuffle' set only, in the centre of one hexagon. We also investigated the (...) stability of an sp 2 hybridization in the core of the dislocation, obtained for one metastable configuration in the 'glide' set. The core structures are characterized in several ways, with a description of the three-dimensional structure, differential displacement maps and derivatives of the disregistry. (shrink)

This article is concerned with one of the notable but forgotten research strands that developed out of French nineteenth-century positivism, a strand that turned attention to the study of scientific discovery and was actively pursued by French epistemologists around the turn of the nineteenth century. I first sketch the context in which this research program emerged. I show that the program was a natural offshoot of French neopositivism; the latter was a current of twentieth-century thought that, even if implicitly, challenged (...) the positivism of first-generation positivists such as Comte. I then survey what French epistemologists—including Ernest Naville, Élie Rabier, Pierre Duhem, Édouard Le Roy, Abel Rey, André Lalande, Théodule-Armand Ribot, Edmond Goblot, and Jacques Picard, among others—had to say about the logic, psychology, and sociology of discovery. My story demonstrates the inaccuracy of existing historical accounts of the philosophical study of scientific discovery. (shrink)