First-principles study of silicon nanocrystals: structural and electronic properties, absorption, emission, and doping.

Total energy calculations within the Density Functional Theory have been carried out in order to investigate the structural, electronic, and optical properties of un-doped and doped silicon nanostructures of different size and different surface terminations. In particular the effects induced by the creation of an electron-hole pair on the properties of hydrogenated silicon nanoclusters as a function of dimension are discussed in detail showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure by an electronic excitation of the cluster is analyzed and considered in the evaluation of the Stokes shift between absorption and emission energies.

[Chronic tonsillitis in childhood: a bacteriological study in connection with benzathine penicillin treatment and the role of bacterial flora in tonsillar hypertrophy].

In this study the authors evaluated the importance of bacteriological study in the diagnostics of chronic tonsillitis in children and investigated the eventuality of modification in superficial as well as parenchymal tonsillar microflora brought about by preventive treatment with benzylpenicillin G. The study further aimed at revealing an eventual relationship between microflora and classic laboratory parameters (haemochromocytometric examination, leukocytic formula, VES, ASLO and urine analysis) as well as at evaluating the possibility of a correlation between the degree of tonsillar hypertrophy and microflora. The 100 patients studied had chronic tonsillitis, were between the ages of 4 and 12 and were all candidates for tonsillectomy.