Recent progress in modeling of cryogenic cavitation for liquid rocket propulsion

Thermal effects substantially impact the cavitation dynamics of cryogenic fluids. The present article reviews recent progress made toward developing modeling and computational strategies to simulate cryogenic cavitation relevant to liquid rocket propulsion applications. We re-examine previously developed cavitation models, including thermal effect and turbulence closures. The experimentally observed "frosty" appearance within the cavity is modeled as a mushy phase boundary. The impact of model parameters and material properties on the prediction is probed by global sensitivity techniques. Performance of the reported cavitation models is compared against the existing cavitation models and experimental data, under both non-cryogenic and cryogenic conditions. Time-dependent computations for various cases of cryogenic cavitation are further reviewed. Impact of the cryogenic environment and inflow perturbations on the flow structure and instabilities is explained via the simulated flow fields and the reduced order strategy of proper orthogonal decomposition (POD). © 2005 Elsevier Ltd. All rights reserved

The effect of cross-linking of chitosan microspheres with genipin on protein release

Genipin, a natural and non-toxic cross-linking reagent, was evaluated for its effects on the drug/protein release and swelling of chitosan microspheres. Chitosan microspheres, using albumin as a model protein, were prepared and cross-linked with 0.5 mM genipin for 4 to 16 h or for 4 h using 0.5 to 2.0 mM genipin. The degree of cross-linking, swelling and the release of albumin from the microspheres was determined by the ninhydrin assay, measuring change in mass between dry and wet spheres, and in 31-day elution tests, respectively. The degree of cross-linking increased up to maximum of 33% to 34% with up to 8 hour cross-linking time or with up to 1.0 mM genipin concentration. Additional cross-linking time or concentration did not significantly increase degree of cross-linking. Swelling ratios decreased significantly from 119.2% in the uncross-linked condition to 108.8% at 16 h cross-linking time. However, increasing the genipin concentration resulted in much smaller decreases in swelling. The release of albumin was reduced with as little as 4 h cross-linking time to 30.9% of uncross-linked microspheres for up to 24 days and by as much as 52.3-60.0% for up to 31 days with 8-16 h cross-linking time. Using genipin concentrations of 1.0 to 2.0 mM for 4 h, greatly reduced albumin release to only 12.4% to 27.1% on day 24. These data demonstrate that protein and drug delivery rates from chitosan microspheres may be controlled and extended by controlling the degree of cross-linking with genipin. © 2006 Elsevier Ltd. All rights reserved

Metabolic functions of Pseudomonas fluorescens strains from Populus deltoides depend on rhizosphere or endosphere isolation compartment

The bacterial microbiota of plants is diverse, with 1,000s of operational taxonomic units (OTUs) associated with any individual plant. In this work we investigate the differences between 19 sequenced Pseudomonas fluorescens strains, isolated from Populus deltoides rhizosphere and endosphere and which represent a single OTU, using phenotypic analysis, comparative genomics, and metabolic models. While no traits were exclusive to either endosphere or rhizosphere P. fluorescens isolates, multiple pathways relevant for plant-bacterial interactions are enriched in endosphere isolate genomes. Further, growth phenotypes such as phosphate solubilization, protease activity, denitrification and root growth promotion are biased towards endosphere isolates. Endosphere isolates have significantly more metabolic pathways for plant signaling compounds and an increased metabolic range that includes utilization of energy rich nucleotides and sugars, consistent with endosphere colonization. Rhizosphere P. fluorescens have fewer pathways representative of plant-bacterial interactions but show metabolic bias towards chemical substrates often found in root exudates. This work reveals the diverse functions that may contribute to colonization of the endosphere by bacteria and are enriched among closely related isolates