Giovanni Ferraris

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An algorithm is presented to derive the twin laws in non-merohedric twins through the systematic search for quasi-perpendicular lattice planes/directions. The twin lattice, i.e. the sublattice common to the whole crystalline edifice built by the twinned individuals, is based on a supercell of the individual defined by a pair of quasi-perpendicular lattice(More)
It is shown that the twin index n calculated, according to Friedel, as a function of the indices (hkl) and [uvw] of the lattice plane and lattice direction defining the cell of the twin lattice applies only to twofold twins, i.e. twins where the twin element is of order 2. For manifold twins, where the twin operation is a three-, four- or sixfold (direct or(More)
The common classification of twinning into the four categories of twinning by merohedry (complete and exact overlap of the lattices of the twinned crystals), pseudomerohedry (complete but approximate overlap), reticular merohedry (partial but exact overlap) and reticular pseudomerohedry (partial and approximate overlap) is revised in terms of the complete(More)
It is shown that one of the main reasons for most failures of the methods for calculating distance-dependent bond strengths is related to the distortion of the coordination polyhedra. The charge distribution (CD) method which depends on only one universal empirical parameter (contraction parameter) is modified to include: (i) an iterative calculation of the(More)
BACKGROUND Archaeological bones contain only small amounts of DNA due to post-mortem DNA degradation and the changes endogenous DNA is subjected to during diagenesis. An important step before undertaking such time-consuming and costly analyses as ancient DNA investigation is to predict the presence of DNA in ancient samples. To date, the leading screening(More)
Prismatic crystals of the title compound, up to 100 microm long and {001} twinned by metric merohedry, were obtained as a side-product of a hydrothermal run devoted to synthesizing the heterophyllosilicate lamprophyllite. Single-crystal X-ray diffraction data were collected on a Bruker-AXS Smart Apex diffractometer from a crystal with approximate(More)
Two new members of the mero-plesiotype rhodesite series [Sr(2)Na(2)(Si(8)O(19)).4H(2)O, abbreviated as TR09; SrNa(4)(Si(8)O(19)).4H(2)O, TR10] have been hydrothermally synthesized in Teflon-lined autoclaves at 503 K and structurally characterized using X-ray diffraction single-crystal data. The crystal structures were solved by direct methods and refined to(More)
In merohedric twinning, the lattices of the individuals are perfectly overlapped and the presence of twinning is not easily detected from the diffraction pattern, especially in the case of inversion twinning (class I). In general, the investigator has to consider three possible structural models: a crystal with space-group type H and point group P, either(More)