Influence of annealing on X-ray diffraction of natural alexandrite
In this work we present results of X-ray diffraction using powder method, on natural alexandrite samples from Minas Gerais State (Brazil), as a function of a sequence of annealing. From these measurements we determine lattice parameters before (a=9.405 Å, b=5.471 Å, c=4.409 Å) and after annealing, and its structure is confirmed as orthorhombic. Measurements done after an annealing of 15 minutes at 700 °C and for 5 hours at 1000 °C indicate the migration of atoms present in the sample through different phases, which were also identified by Microprobe Analysis (WDS). However we have verified that such migration does not modify the structure. X-ray diffraction measurements have been carried out in conjunction with optical absorption in the UV–Vis as a function of annealing.
Transmission Electron Microscope Study of Anti‐Phase Boundaries in Alexandrite (Al2−xCrxBeO4)
A study has been made of the diffraction contrast fringe patterns observed by transmission electron microscopy in alexandrite (Al2—xCrxBeO4), the chromium bearing variety of chrysoberyl. Evidence is presented that the fringe patterns are due to anti-phase boundaries resulting from faults in the cation stacking within the same oxygen lattice. Models for the probable ionic configuration of such boundaries are proposed and discussed. It is shown that the diffraction contrast fringe patterns observed with different operating reflections are consistent with those expected from the proposed models. 
 
 
 
Es wurden Beugungskontraststreifenbilder untersucht, die durch Transmissionselektronenmikroskopie in Alexandrit (Al2—xCrxBeO4), die Chrom enthaltende Variante des Chrysoberyll, beobachtet wurden. Es wird bewiesen, das die Streifenbilder durch Antiphasengrenzen hervorgerufen werden, die von Fehlern der Kationenstapelung innerhalb desselben Sauerstoffgitters stammen. Modelle fur eine mogliche Ionenkonfiguration solcher Grenzen werden vorgeschlagen und diskutiert. Es wird gezeigt, das die Beugungskontraststreifenbilder, die mit unterschiedlichen Arbeitsreflexionen beobachtet wurden, mit denen ubereinstimmen, die fur die vorgeschlagenen Modelle erwartet werden.
The structure of electricity demand in the Brazilian household sector
Abstract The present structure of residential electricity demand is analysed by electricity consumption classes and end-uses. Nearly 70% of households consume less than 150 kWh/month and are responsible for 35% of total residential demand. Other determinants of electricity-use, such as income and place of residence, are also discussed. It is found that electricity demand is increasing faster than income as the country reaches appliances saturation in upper consumption levels. Water heating and refrigeration account for the major part of residential consumption. Residential conservation efforts have started introducing more efficient lighting equipment and refrigerators, but further work will have to be done to speed up the diffusion of efficient technology at costs that can be paid by consumers.