A search to find spatially resolved nova shells was carried out; two new shells (around FH Ser 1970 and V533 Her 1963) were discovered. The angular sizes measured at the current epoch of the eight previously known shells around novae which erupted prior to 1945 imply that the shells are coasting out at constant velocity. Expansion velocities, interstellar absorptions, and masses of the ejected material were determined for several recent novae. A new calibration of the maximum visual luminosity-rate of decline relationship for galactic novae is given. Subject headings: nebulae: general -stars: novae
Increasing the aromatic ring content of polyamides results in increased melting points and fiber stiffness. These intractable polymers generally cannot be melt-spun or solutionspun from conventional spinning solvents. A search for general classes of solvents for intractable polyamides resulted in the conclusion that the solvent must act as a sufficiently strong Lewis acid to complex the polymer and have sufficient solvent power to dissolve the resulting complex. Examples are given of this two-step mechanism for solution formation.This led to the selection of concentrated sulfuric acid as a polyamide wet-spinning solvent. Extrusion of sulfuric acid solutions of polyamides into aqueous sulfuric acid is shown to be a general fiber-forming process. The fiber-forming mechanism is interpreted in terms of acid-base reactions, the diffusion of the solvent and precipitant, and the kinetics of precipitation of polymer from supersaturated solution. Diffusion effects in the extreme case led to "incursions" which result in a brittle fiber structure. These are illustrated with the help of motion picture microscopy. The relationships of these physico-chemical phenomena to fiber properties are discussed. , 0 .
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