Silicon-rich silicon oxide thin films have been prepared by thermal evaporation of silicon monoxide in vacuum. The SiOx film composition (1.1⩽ x ⩽1.7) has been controlled by varying the deposition rate and residual pressure in the chamber. Long time stability of all films has been ensured by a postdeposition annealing at 523 K for 30 min in Ar atmosphere. Some films were further annealed at 973 K and some others at 1303 K. Raman scattering measurements have implied the formation of amorphous silicon nanoparticles in films annealed at 973 K and Si nanocrystals in films annealed at 1303 K. The latter conclusion is strongly supported by high resolution electron microscopy studies which show a high density of Si nanocrystals in these films. Photoluminescence has been observed from both amorphous and crystalline nanoparticles and interpreted in terms of band-to-band recombination in the nanoparticles having average size greater than 2.5 nm and carrier recombination through defect states in smaller nanoparticles.
To examine the effect of hypothermia on the phagocytic capacity of rat peritoneal macrophages for latex particles, male Wistar rats were exposed to 4 degrees C for 8 and 72 h. While the shorter exposure to cold did not affect body temperature and macrophage function, animals exposed to 4 degrees C for 72 h showed a mean decrease of their body temperature by 1.5 degrees C. The superoxide anion production was significantly increased whereas the number of phagocytic cells decreased. In addition, the mean number of latex particles engulfed by each individual cell was lower than that of controls. Peripheral blood mononuclear cells (PBMC) of these animals showed lower mitogen response to phytohaemagglutinin (PHA), while that for concanavalin A (Con-A) remained unchanged. Peritoneal macrophages exposed in vitro to 24 degrees C for 60 min showed a decreased phagocytic capacity in comparison with macrophages kept at 37 degrees C, an observation suggesting the development of an indigenous cell defect for phagocytosis at lower temperatures. On the other hand, the effect of additional humoral factor(s) on macrophage activity, such as an increase in serum level of catecholamines and corticosterone, cannot be excluded. The results of the study may contribute to understanding the predisposition to infections during exposure to cold.
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