Development of reusable liquid-hydrocarbon-fueled hypersonic vehicles requires improved understanding of the effect of chemical composition on the controlling reaction chemistry and deposition propensity as the fuel is used to cool the system. In this effort, supercritical pyrolytic stressing studies were performed using two petroleum-derived fuels and a Synthetic Paraffinic Kerosene (SPK) comprised predominantly of normal and branched paraffins. All fuels decomposed via free radical pathways with high yields of unsaturates and lower molecular weight products consistent with pyrolysis at high pressures and moderate temperatures. However, the SPK was significantly more reactive than the petroleum-derived fuels due to a lack of efficient hydrogen donors that act to terminate chain reactions (higher net propagation rate). High-pressure liquid chromatography was used to identify and quantify polycyclic aromatic hydrocarbons (PAH) in the stressed fuels, conclusively determining that these are produced during thermal stressing. A notable observation was the presence of PAH during SPK stressing, as the neat fuel did not contain cyclic precursors for growth to PAH. During stressing with stainless-steel tubing, the formation of filamentous deposits via metal-catalyzed reactions of stressed fuel components with reactor surfaces was observed for all fuels studied. However, the SPK fuel exhibited a much higher pyrolytic deposition rate, which was attributed to higher lateral growth rates of surface filaments via noncatalytic free radical addition pathways. The PAH formed during SPK stressing are indicators of the highly reactive intermediates prone to participating in the surface coke addition pathways. Studies blending benzene with the SPK indicated that low PAH solubility in the paraffinic fuel is not the dominant cause for the high deposition propensity. Testing with the petroleum-derived fuels showed that metal sulfide filament formation can occur under endothermic conditions, and higher fuel sulfur content can increase carbon deposition propensity. Studies with surface passivated tubing (Silcosteel) suppressed filamentous carbon formation and rendered a substantial reduction in SPK deposition to levels similar to the petroleum-derived fuels. Overall, these studies provided guidance regarding the controlling chemistry during supercritical pyrolysis of current and potential synthetic hydrocarbon fuels and insight into prevalent deposition pathways.

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The differential stability of biochemistry and molecular biology Web page resources based on their domain designation is described. Many teachers have been excited by the potential enrichment of placing hyperlinks to Internet distributed educational resources within the class materials available to their students. However, there seems to be a belated realization that such hyperlinked resources are not necessarily stable and often disappear, causing frustration for both instructor and students. We recently developed three graduate-level biochemistry and molecular biology courses for distance delivery to high school teachers that relied heavily on such Web-based distributed resources. The 515 hyperlinked Web pages in these courses represent a set of authentic science education resources that were monitored for 24 months since their creation (August 2000). During this time, over 20% of the URLs have been victims of "link rot," becoming nonviable, moving without automatic forwarding, or having their content changed.

C. V. Philip and David W. Brooks consistent with the data in Table V. Although the relative constancy of klp does not establish the pathway as being FeOH + HL for all these systems, this fact, plus the other observations, argues for the assignment of the rate constants to ks as indicated in Table V. If fcip is on the order of 101 sec"1 for the kx pathway, then the contributions from this pathway to the measured rate would be quite small for ligands which are mostly protonated in acid solutions.