Poor school performance by adolescent students has been attributed in part to insufficient sleep. It is recognized that a number of factors lead to diminished total sleep time and chief among these are early school start times and sleep phase delay in adolescence. Political initiatives are gaining momentum across the United States to require later school start times with the intent of increasing total sleep time and consequently improving school performance. Later school start times come with significant costs and impact other activities of families and communities. The decision to implement later school start times cannot be made lightly and deserves support of well-performed research on the impact of these changes. A study evaluating the association of academic performance and total sleep time was performed in middle school and high school students in a suburban Maryland school system. Preliminary results of this study show no correlation of total sleep time with academic performance. Before mandating costly changes in school schedules, it would be useful to perform further research to determine the effects of increasing sleep time on the behaviors of adolescent students.

Poor school performance by adolescent students has been attributed in part to insufficient sleep. It is recognized that a number of factors lead to diminished total sleep time and chief among these are early school start times and sleep phase delay in adolescence. Political initiatives are gaining momentum across the United States to require later school start times with the intent of increasing total sleep time and consequently improving school performance. Later school start times come with significant costs and impact other activities of families and communities. The decision to implement later school start times cannot be made lightly and deserves support of well-performed research on the impact of these changes. A study evaluating the association of academic performance and total sleep time was performed in middle school and high school students in a suburban Maryland school system. Preliminary results of this study show no correlation of total sleep time with academic performance. Before mandating costly changes in school schedules, it would be useful to perform further research to determine the effects of increasing sleep time on the behaviors of adolescent students.

This work aims to investigate how some significant atomising parameters influence the mass median particle size d 50 of water atomised metal powders. More specifically, these were water pressure, melt flowrate, water jet angle, liquid metal viscosity and surface tension. Existing models for the prediction of d 50 during water atomisation were reviewed. The selected models were fitted and compared with atomising experiments of liquid iron containing 0?5-4?4%C. Experimental results and model calculations were used in a parameter study to investigate how the different parameters influenced d 50 . The effect on d 50 was large for the water pressure, medium for the viscosity and low for the melt flowrate and surface tension. Model calculations indicate that the jet angle has a large effect on d 50 , which should be verified by additional studies. The model proposed by Bergquist (B. Bergquist: Powder Metall., 1999, 42, 331-343) showed the best agreement with the current experimental data.

Differential ThermalAnalysis (DTA) and Directional Solidification and Quenching (DSQ) were used to evaluate the solidification and precipitation sequence for the Ni-base superalloys IN718, IN625 and IN939. They all showed a similar precipitation sequence, with an initial precipitation of γ dendrites, followed by an intermediate non-invariant divorced eutectic reaction of type L-* γ + MC, and a final eutectic precipitation of Laves phase for alloy IN718 and IN625 and of /7-phase for alloy IN939. The reaction temperatures and the amounts of carbides and of final precipitates were evaluated. Precipitated nitrides were found to act as nucleation sites for the precipitation of blocky carbides/carbonitrides, at low interdendritic supersaturation, while in interdendritic regions with high supersaturation, a 'script-like' carbide formation was found instead.Brought to you by | Purdue University Libraries Authenticated Download Date | 5/31/15 11:04 AM

A two-dimensional non-steady state computational fluid dynamic model was employed to gain a basic understanding of the flow in the ingot during casting. The surface velocity was found to be affected by the inlet angle and was found to vary with the casting level. The information of surface velocity was related to the probability of the inclusion removal. Water model experiments were also conducted to help the understanding. The model calculation revealed the same trends as the results of water model experiments. Both computational fluid dynamic data and the physical modelling showed that the inlet angle of 5u currently used in the industry was a good alternative regarding inclusion removal. The present work suggests strongly that the melting shop should try to obtain a liquid or semiliquid film at as early stage as possible in ingot casting.