Temperature Anisotropies in a Universe with Global Defects

We present a technique of calculating microwave anisotropies from global defects in a reionised universe. We concentrate on angular scales down to one degree where we expect the nongaussianity of the temperature anisotropy in these models to become apparent.Comment: 12 pages, uuencoded postscript. To appear in the Proceedings of the Case Western Reserve University CMB Meeting. PUPT-94-148

The Sinterability of Ultra-Fine Iron Powders.

Iron powders having a high specific surface area, compared to current industrial iron powders, have been prepared by the decomposition and Subsequent reduction of ferrous oxalate, and by the reduction of a high purity grade of oxide, at 300 C, under a hydrogen atmosphere. The iron powders obtained were pyrophoric, so that all handling was carried out in glove boxes, under an argon atmosphere. The morphology of the powders was studied using electron microscopic and krypton sorption (BET) techniques. Both preparation routes yielded powders of similar shape and size although considerable differences existed in the oxides from which they were prepared. The sintering behaviour of the powders was studied at temperatures up to 900°C and for times up to 16 1/2 hours. A typical industrial iron powder viz carbonyl iron, was sintered alongside the fine powders to provide a basis for comparison. Marked differences were observed in sintering behaviour, the iron powder ex oxalate showing a rapid initial densification followed by an apparent cessation of densification. The other two powders showed more conventional behaviour up to 900 C. However on sintering at 900°C rapid drops in density were observed in both these powders, accompanied by an abnormal rate of grain growth at this temperature. The other powder, ex ferrous oxalate, showed a smaller drop in density and a more gradual rate of grain growth. Activation energies for sintering fell below the established values for grain boundary diffusion in iron, and this is interpreted in terms of the operation of more than one sintering mechanism acting in parallel with each other. Diffusion distances obtained from bulk diffusion data, are compared with actual grain sizes present in the materials, in order to discuss the relative contributions of both boundary and volume diffusion in terms of the proximity of grain boundary sinks. It was concluded that finer grain sizes resulted in a larger contribution of volume diffusion to sintering owing to a longer contact between pores and the grain boundary sink. Differences between the iron powder ex oxalate, and the other two materials are accounted for in terms of purity, since the much lower rate of grain growth in this former powder is primarily responsible for its densification characteristics, and such grain growth is markedly affected by purity. A dilatometric investigation was carried out on the sintered compacts, in order to determine the temperature of the alpha/gamma phase change in the materials. It was found that both carbonyl iron and iron powder ex oxalate would contain phase on sintering at 900°C, whereas transformation in the powder from high purity oxide occurred above this sintering temperature

The Hybrid Master\u27s Degree: Combining Research with Practice

The article discusses the development of a hybrid master degree program by the Donald W. Reynolds School of Journalism at the University of Nevada in Reno. Since the journalism faculty of the school is too small to offer a full-service master\u27s degree, the school developed a hybrid program that integrates systematic research with practice-based education. The program is designed to equip students with knowledge in academic research in preparation to doctoral studies. The program also emphasizes the study of mass media to prepare students for professional careers in broadcast journalism

Fatigue failure of regenerator screens in a high frequency Stirling engine

Failure of Stirling Space Power Demonstrator Engine (SPDE) regenerator screens was investigated. After several hours of operation the SPDE was shut down for inspection and on removing the regenerator screens, debris of unknown origin was discovered along with considerable cracking of the screens in localized areas. Metallurgical analysis of the debris determined it to be cracked-off-deformed pieces of the 41 micron thickness Type 304 stainless steel wire screen. Scanning electron microscopy of the cracked screens revealed failures occurring at wire crossovers and fatigue striations on the fracture surface of the wires. Thus, the screen failure can be characterized as a fatigue failure of the wires. The crossovers were determined to contain a 30 percent reduction in wire thickness and a highly worked microstructure occurring from the manufacturing process of the wire screens. Later it was found that reduction in wire thickness occurred because the screen fabricator had subjected it to a light cold-roll process after weaving. Installation of this screen left a clearance in the regenerator allowing the screens to move. The combined effects of the reduction in wire thickness, stress concentration (caused by screen movement), and highly worked microstructure at the wire crossovers led to the fatigue failure of the screens

Performance of a Coal Refuse Embankment

Continuous determinations of density, moisture content, and permeability through a 140-foot high coarse refuse embankment impounding slurry were made. The density determinations were made with nuclear moisture-density depth gauges continuously throughout 120-foot depth of the embankment. The permeability tests were made with a special packer permeability device and were conducted throughout the 120-foot depth of the embankment. Compaction density tests were made during compaction of the refuse. Comparisons were made to design, as-compacted, and in-place permeabilities, densities, and phreatic surface within the embankment. The study shows that coarse refuse embankments compacted in roughly 18-inch lifts with a special dozer and haulage equipment perform well in terms of comparisons of in-situ parameters to design parameters for seepage, density, and strength

Causality, randomness, and the microwave background

Fluctuations in the cosmic microwave background (CMB) temperature are being studied with ever increasing precision. Two competing types of theories might describe the origins of these fluctuations: ``inflation'' and ``defects''. Here we show how the differences between these two scenarios can give rise to striking signatures in the microwave fluctuations on small scales, assuming a standard recombination history. These should enable high resolution measurements of CMB anisotropies to distinguish between these two broad classes of theories, independent of the precise details of each.Comment: uuencoded tex file and 4 postscript figure files, 8 pages. Also available at http://euclid.tp.ph/Papers/index.html; Changes: Minor changes reflect final published versio