The mechanisms involved in the induction and maintenance of self-tolerance remain unclear. The traditional point of view is that self-reactive cells are eliminated by clonal deletion (1) and many specific mechanisms, such as receptor blockade (2), have been proposed for achieving this. A more recent, contrasting point of view (3, 4) is that self-tolerance is achieved through regulatory procedures which produce active suppression.
Exogenous NO induces retinal neurotoxicity, suggesting that NO plays a pathogenic role in degenerative retinal diseases. BDNF and CNTF protect retinal neurons from NO-mediated neurotoxicity.
The microstructural changes of a simulated waste glass irradiated with doping of 238pu and 244Cm were observed by use of a preshadowed carbon replica technique in combination with scanning electron microscopy (SEM). The irradiated glass was annealed and its microstructural changes after annealing were observed by use of the sametechnique.In the glass irradiated at a dose of 2.75x1025 α-decays/m3, bubbles with a radius from 0.15μrm to 0.35μm were observed. The average bubble radius and the bubble density were 0.23μm and 1x1017 bubbles/m3, respectively. Using these observed values, the volume change of the glass resulting from the bubble formation was estimated to be + 0.51 %. This valuoof + 0.51 % was close to the volume change of the irradiated glass measured in our previous study, which suggests a large portion of the volume change by α-irradiation results from bubble formation. In the glass annealed after irradiation the average bubbleradius was observed to decrease with annealing time. The bubble radius as a function of annealing time was analyzed on the basis of the helium diffusion model with two chemicalprocesses, i.e. trapping at bubbles and re-solution from bubbles into glass matrix. The values of the diffusion coefficient of helium, the trapping parameter and the re-solution parameter, which had been obtained experimentally in our previous study on the helium release, were applied to the calculation. The calculated curve was in good agreement with the observed data.
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