Design, test, and evaluation of three active flutter suppression controllers

Three control law design techniques for flutter suppression are presented. Each technique uses multiple control surfaces and/or sensors. The first method uses traditional tools (such as pole/zero loci and Nyquist diagrams) for producing a controller that has minimal complexity and which is sufficiently robust to handle plant uncertainty. The second procedure uses linear combinations of several accelerometer signals and dynamic compensation to synthesize the model rate of the critical mode for feedback to the distributed control surfaces. The third technique starts with a minimum-energy linear quadratic Gaussian controller, iteratively modifies intensity matrices corresponding to input and output noise, and applies controller order reduction to achieve a low-order, robust controller. The resulting designs were implemented digitally and tested subsonically on the active flexible wing wind-tunnel model in the Langley Transonic Dynamics Tunnel. Only the traditional pole/zero loci design was sufficiently robust to errors in the nominal plant to successfully suppress flutter during the test. The traditional pole/zero loci design provided simultaneous suppression of symmetric and antisymmetric flutter with a 24-percent increase in attainable dynamic pressure. Posttest analyses are shown which illustrate the problems encountered with the other laws

Recombinant production and characterisation of two Fasciola hepatica cathepsin L proteases

The cysteine proteases of the liver fluke, Fasciola hepatica, are of great importance to the virulence of the organism. Previous work has established the involvement of these enzymes in catabolism, migration through host tissues and defence against host immune attack. They have therefore been identified as important vaccine targets. In this study, sequence analyses compare the F. hepatica cathepsins LI and L2 with each other and with other cathepsin Ls of F. hepatica and the related parasite, F. gigantica. Groupings of enzymes based on propeptide and active site cleft sequences are established, indicating possible functional diversity in both species. Comparisons with other trematode and mammalian cathepsin Ls were also performed, focusing on a propeptide motif involved in enzyme processing. Production of the recombinant enzymes was by expression in the Pichia pastoris yeast expression system, providing sufficient quantities of enzyme for characterisation studies. Enzyme activity against fluorogenic substrates and native collagens was compared, demonstrating differences in substrate specificity and therefore possible function between the two enzymes. Processing and activation of the enzymes was also investigated, with inactive mutant enzymes produced for this purpose. Finally, details are given of various collaborations with other laboratories utilising the recombinant enzymes produced during this project