Scapolite : alkali atom configurations , antiphase domains , and compositional Yariations
Electrostatic energy calculations on an intermediate scapolite indicate that Na+ should prefer to be adjacent to Clanions and Ca2* to be adjacent to CO3radicals. The calculations also indicate that short-range ordering of NarCl and CaaCO3 clusters is energetically favored and might give rise to antiphase domains. Electrical neutrality considerations on the anion/radical site in scapolite suggest that the unusual compositional variations observed in the marialite-meionite series are the result of crystallographic constraints on the two possible independent exchange reactions in scapolite: NaCICaCO-3 and NaSie6-Ai. The compositions of naturally occurring scapolites may be explained in terms of the scapolite composition that represents local charge balance between Ca2*, Na* cations and Cl-, COIanions.
Electron-gas theory of ionic crystals, including many-body effects
The electron-gas theory of ionic crystals is extended to include nonadditive (many-body) interactions arising from the simultaneous overlap of the densities of several ions. The theory is used to predict equilibrium geometries, lattice energies, and pressure-induced phase transitions for the fluorides and oxides of the alkali and alkaline earth metals. The results are in good agreement with electron-gas calculations assuming additive, two-body interactions between pairs of ions. This comparison shows that the simultaneous overlap of three or more ions has only a small effect on these crystals, and that for many purposes the simpler two-body approximation is adequate. The predictions of lattice distances and energies agree with experiment to a typical accuracy of 1 or 2%. In order to obtain this accuracy, it is necessary to calculate the electron densities for the anions in a stabilizing potential well whose size is determined self-consistently by the electrostatic potential of the crystal at the anion site. This shrinkage of the anion by the crystal is also a kind of many-body interaction, but it can be handled within the framework of an effective two-body interaction involving the stabilized anions. The corresponding cation expansion effect is also calculated, and shown to be negligible for the alkali and alkaline earth metal ions.
Detection of Fractures Based on Directional Filtering in Image Logging
According to the feature of the direction of fractures in image logging, a method of fracture detection in image logging based on directional filtering is presented in this paper. The fracture image is filtered by the corresponding filter based on the local direction of fractures, which enhances the fracture traces in the direction of fractures in image logging. The final fracture traces are extracted by the combination of the results of both directional filtering and the threshold segmentation. Experimental results show this method effectively detect the fractures in image logging.