Les Dislocationsby J. Friedel

Analysing Friedel averages and differences.

Various practical applications of the average (A) and difference (D) of Friedel opposites are described. Techniques based on the resonant-scattering contribution to Friedel differences are applied to see whether a crystal is centrosymmetric or not, and to determine the point group of the crystal. For the validation of a structural study, plots of A(obs) against A(model), and D(obs) against D(mo...

Intensity statistics of Friedel opposites.

A previous analysis of the average intensity and mean-square intensity difference of Friedel opposites, confined to the space group P1 [Flack & Shmueli (2007). Acta Cryst. A63, 257-265], is here extended to all the non-centrosymmetric space groups. The present analysis presumes purely non-centrosymmetric content of the unit cell. An important result of this study is that the average intensity a...

TiGePt--a study of Friedel differences.

The X-ray single-crystal diffraction intensities of the intermetallic compound TiGePt were analysed. These showed beyond doubt that the crystal structure is non-centrosymmetric. The analysis revolves around the resonant-scattering contribution to differences in intensity between Friedel opposites hkl and \bar h\bar k\bar l. The following techniques were used: R(merge) factors on the average (A)...

Les maladies causées par les anaérobies pathogènes sporulés chez les animaux domestiques

Les Rotations Et Les Quaternions

La construction du corps non commutatif H de quaternions est une variante plus compliquée de la construction du corps commutatif C de nombres complexes. Donc on commence en rappelant la construction de C à partir de R. Les nombres complexes s’écrivent a+ bi avec a, b ∈ R. Donc C est un espace vectoriel sur R de dimension 2 avec base {1, i}. La loi d’addition de C est celle que C possède en tant...