In contrast to graphite, MoS2 retains its lubrication properties in vacuum. The coefficient of friction of MoS2 powder, compressed into pellets, has been measured under high vacuum conditions. Well run-in surfaces, which have been stationary for a period of time, show higher friction initially upon resumption of sliding. Presence of an amorphous layer of sulfur during sliding is postulated.

An evaluation of the consistency between the absolute voltage determination of the threshold energy of the Li 7 (/>,»)Be 7 reaction as measured by Herb, Snowdon, and Sala and earlier independent absolute alphaparticle energy measurements has been made. The experimental comparison was affected by employing the natural alpha-particles from polonium and radium C, the energy of which has been measured absolutely by several authors using magnetic deflection methods. In this experiment the alpha-particles from these substances have been electrostatically deflected in the 90° cylindrical electrostatic analyzer at the University of Wisconsin. Alpha-particle line measurements were analyzed by numerical integration of resolution and source functions and in themselves contributed negligibly to the uncertainties of the comparison. The resulting alpha-particle energies, evaluated by comparison with the energy of the Li 7 (^,«)Be 7 threshold, agree with earlier measurements, and indicate that within the limits of accuracy of the experiments, all determinations give identical results.

This research presents the experimental characterization and modeling of three-dimensional unsteady-state temperature and degree of cure distributions for the pultrusion manufacturing of fiberglass-epoxy I-beam composites. The model is capable of predicting temperature and degree of cure distributions for composites with Cartesian shapes in three dimensions and temperature profiles in pultrusion dies without the aid of predetermined temperature values used as die wall boundary conditions. The numerical model is compared with experimentally measured temperatures and degrees of cure recorded during the actual pultrusion manufacturing of the fiberglass-epoxy I-beams. Using a differential scanning calorimeter (DSC), the die composite exit degree of cure was also obtained. The finite volume method was utilized in the development of the numerical model for solving the governing energy and species equations used in modeling the entire heating section of the pultruder. The combinations of pull speed, fiber volume, and die temperature profiles can be modeled very economically to simulate pultrusion manufacturing of composites. Since this research is not limited in terms of predetermined temperature values, it can be tailored easily to predict a multitude of temperature profiles suited for a pultrusion process. This research is also important because it provides realistic modeling of irregular cross-sectional geometries.

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This work was sponsored by the AEC. 1 J. Steinberger, W. Panofsky, and J. Steller, Phys. Rev. 78, 802 (1950). 2 K. Brueckner, Phys. Rev., in press. His calculations of radiative corrections did not include effects from virtual neutral mesons, but it does not seem that this would change his results in a qualitative manner.3