15,247 research outputs found
High-temperature ''hydrostatic'' extrusion
Quasi-fluids permit hydrostatic extrusion of solid materials. The use of sodium chloride, calcium fluoride, or glasses as quasi-fluids reduces handling, corrosion, and sealing problems, these materials successfully extrude steel, molybdenum, ceramics, calcium carbonate, and calcium oxide. This technique also permits fluid-to-fluid extrusion
Fresnel concentrating collector
An advanced point focusing solar technology demonstrated potential for near term commercialization as a renewable energy technology. The design features combine to produce a highly efficient, low cost, safe, adaptable, durable system which is simple to manufacture, install and maintain
Vortices in self-gravitating disks
Vortices are believed to greatly help the formation of km sized planetesimals
by collecting dust particles in their centers. However, vortex dynamics is
commonly studied in non-self-gravitating disks. The main goal here is to
examine the effects of disk self-gravity on the vortex dynamics via numerical
simulations. In the self-gravitating case, when quasi-steady gravitoturbulent
state is reached, vortices appear as transient structures undergoing recurring
phases of formation, growth to sizes comparable to a local Jeans scale, and
eventual shearing and destruction due to gravitational instability. Each phase
lasts over 2-3 orbital periods. Vortices and density waves appear to be coupled
implying that, in general, one should consider both vortex and density wave
modes for a proper understanding of self-gravitating disk dynamics. Our results
imply that given such an irregular and rapidly changing, transient character of
vortex evolution in self-gravitating disks it may be difficult for such
vortices to effectively trap dust particles in their centers that is a
necessary process towards planet formation.Comment: to appear in the proceedings of Cool Stars, Stellar Systems and The
Sun, 15th Cambridge Workshop, St. Andrews, Scotland, July 21-25, 200
Apollo experience report: The cryogenic storage system
A review of the design, development, and flight history of the Apollo cryogenic storage system and of selected components within the system is presented. Discussions are presented on the development history of the pressure vessels, heaters, insulation, and selected components. Flight experience and operational difficulties are reported in detail to provide definition of the problems and applicable corrective actions
Star formation and the distribution of HI and infrared emission in M51
H I, infrared, CO, H alpha and beta band observations of M51, the prototypical grand-design spiral galaxy, are used to study the consequences of star formation for the distribution of H I and dust. Using the H I and CO data sets new tests of the idea that the H I is largely a dissociation product in star-forming regions were performed. It was confirmed that the H I spiral arms are generally coincident with the H II region arms, and offset downstream from the CO arms. The radial distributions of total gas, H alpha and H I surface density have a simple explanation in the dissociation picture. The distributions also demonstrate how the surface density of H I might be related to the star formation efficiency in molecule-rich galaxies. The large width of the H I regions along the arms compared to that of the H II regions can be understood in terms of a simple Stroemgren sphere calculation. The longer lifetime of the stars producing dissociating radiation vs. those producing ionizing radiation will also contribute to the greater width of the H I arms if stars are continuously forming on the arms. The lack of detailed coincidence of the H I and H II regions along the inner arms has a variety of possible explanations within the dissociation scenario. Two simple tests to probe the origin of the IRAS emission in M51 were performed
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