X-ray diffraction in superabsorbing crystals: absorption intrinsic width.

The several mathematical formulations of X-ray diffraction theory facilitate its understanding and use as a materials characterization technique, since one can opt for the simplest formulation that adequately describes the case being studied. As synchrotrons advance, new techniques are developed and there is a need for simple formulations to describe them. One of these techniques is soft resonant X-ray diffraction, in which the X-rays suffer large attenuation due to absorption. In this work, an expression is derived for the X-ray diffraction profiles of reflections where the linear absorption is far greater than primary extinction; in other words, the crystal is superabsorbing. The case is considered of a parallel plate crystal, for which the diffraction profile of the superabsorbing crystal is computed as a function of crystal size normal to the diffraction planes. For thin crystals or those with negligible absorption, the diffraction profile of a superabsorbing crystal coincides with the result of the kinematical theory. For thick crystals, the absorption intrinsic profile is obtained, described by a Lorentzian function and characterized by the absorption intrinsic width. This absorption intrinsic width is proportional to the linear absorption coefficient and its expression is similar to that for the Darwin width, while the absorption intrinsic profile is a special case of the Laue dynamical theory, and it is similar to the Ornstein-Zernike Lorentzian. The formulation of X-ray diffraction of superabsorbing crystals is simple and provides new perspectives for the soft resonant X-ray diffraction technique.

Pathogenic characteristics of yeasts isolated from vaginal secretion preserved under mineral oil

In order to evaluate the pathogenicity of yeasts isolated from vaginal secretion of pregnant and non-pregnant women - stored in mineral oil at the URM Mycology Collection, Department of Mycology, Federal University of Pernambuco - 30 samples belonging to the genera Candida, Rhodotorula, Trichosporon, and Kloeckera, were studied regarding their pathogenic characteristics, ability to grow at room temperature (28°C ± 1°C), 37°C, and 42°C for 72 hours, and production of both phospholipase and proteinase. Results showed that all 30 isolates (100%) were able to grow at room temperature and 37°C, and that 17 samples (57%) were able to grow at 42°C. Evaluation of enzymatic activity showed protease activity in only two isolates (7%), namely C. maritima and C. obtusa. Phospholipase activity was detected in 20 isolates (67%) using soy lecithin as substrate at different temperatures. The characterization of yeasts isolated from vaginal secretion and determination of their enzymatic activity may contribute to understanding the epidemiology of vulvovaginitis and assist in the treatment of patients.