Fuel Regression Mechanism in a Solid Fuel Ramjet

A model relating the combustion characteristics, particularly the regression rate, to the fuel properties in a solid fuel ramjet (SFRJ), is presented. The analysis is based on inspecting the different phenomena (e.g., chemical kinetics and heat transfer) involved in the fuel decomposition process in order to determine the rate controlling steps, and modeling the important mechanisms. Model predictions were compared to experimental findings for four polymeric fuels, showing excellent qualitative agreement in classifying different fuels, as well as good quantitative predictions of the fuel regression rates. The model can serve as a useful tool for the selection of appropriate fuels, as well as for preliminary design of the engine and mission profile prior to static firings of the final SFRJ prototype.     

Reactivity of CO2 on Clean and Hydrogen-Covered Rhenium Single Crystal Surfaces

The adsorption and dissociation of CO₂ were studied on clean and H₂-precovered Re(0001) and Re(1120) surfaces. Molecular CO₂ lies linear and parallel to the surface at crystal temperatures below 115 K, as indicated by high-resolution electron energy loss spectroscopy. Upon heating the surface during temperature-programmed desorption experiments, a fraction of the molecules dissociates. It is found that dissociation is more effective on the smooth Re(0001) surface than on the rough Re(1120) one. A model for a possible active site which may account for the observed structure sensitivity is discussed. At adsorption temperatures above 150 K, a sharp decrease in the dissociation probability is observed, which is explained in terms of a faster competing desorption process. H₂ preadsorbed on Re(0001) was found mostly to block the adsorption of molecular CO₂ and to destabilize the adsorbate. As a result, the dissociation of CO₂ decreases with increasing H₂ coverage.     

Immunotherapy of tumors expressing IGF-I

Male and female rats were divided into two groups: stress (20 min of immobilization) and no stress. All animals were then given either one or three palatable foods for a 2 h test session. Each rat received both the single (one food) and variety (three foods) conditions twice, in a balanced order, in an ABAB experimental design. Stressed animals ate less than nonstressed animals. Animals ate more in the variety condition than in single condition during the first set of test sessions only. The stimulating effect of variety on food intake was not evident during the replication of conditions. All animals ate more of the palatable test foods than chow in a comparable time period. Rats ate more with each successive test session (regardless of food variety condition), showing a relative stabilization of food intake from the third to the fourth test sessions. However, there was a significant interaction of stress condition, sex, and test session. Stressed females continued to increase their food intake from the third to the fourth test session such that there was no longer any difference between the stressed and nonstressed females during the last test session. These results suggest that the effect of variety on food intake habituates when the same test foods are used repeatedly, and that there is no difference between males and females in the response to variety. Furthermore, while stress reduces the intake of palatable foods in all animals, females may show an habituation to this effect.