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Radiation-induced void swelling was studied in high-purity and nitrogen-doped Fe-16Cr-20Ni alloys by irradiation in a high-voltage electron microscope at 500°C. The nitrogen concentrations were determined at various stages of preparation by neutron and photon activation analysis. Although some contamination occurred during sample preparation the nitrogen contents in the samples ready for irradiation are similar to those found in the massive starting alloys. They are about 90 and 400 wtppm in the doped alloys and about or less than 10 wtppm in the pure alloys. Nitrogen significantly reduces the swelling. For 90 wtppm, the effect is mainly a delay in the beginning of swelling, whereas there is an important decrease of the swelling rate for 400 wtppm with almost no delay. Such minor concentrations of metalloidic impurities should be considered in the interpretation of the swelling behaviours of materials usually considered as highly pure.

The application of combinatorial optimization techniques to the automatic spacecraft scheduling problem is described. The problem is to search over the candidate sequences of experiments for a sequence that maximizes the value of the science conducted while minimizing constraint conflicts. Exploratory computational results indicate that pseudorandom research techniques, such as simulated annealing, generate viable sequences in reasonable times. >

It has been shown that the sera of patients with cystic fibrosis reveal more numerous and frequent antibody responses to extracellular products of strains of Staphylococcus aureus than do sera from control subjects of a similar age, time and place. In a significant percentage of patients with cystic fibrosis multiple antibody responses were found against extracts of a Hemophilus influenzae strain. Such multiple antibodies were not seen in sera of the control group. These findings suggest that this organism may not infrequently be involved in the pathogenesis of the pulmonary lesions. Many more patients with cystic fibrosis than controls failed to reveal antibodies against the extracellular products of a strain of group A hemolytic streptococcus. No detectable antibodies were found in any of the sera against pneumococcal type 2 polysaccharide, old tuberculin or a mouse peritoneal toxoplasma concentrate. The potential value of this approach for the analysis of the underlying etiologic agents involved in the respiratory infections of patients with cystic fibrosis is discussed.