Regulation of nonlinear systems using conditional integrators

This paper studies the regulation of nonlinear systems using conditional integrators. Previous work introduced the tool of conditional integrators that provide integral action inside a boundary layer while acting as stable systems outside, leading to improvement in transient response while achieving asymptotic regulation in the presence of unknown constant disturbances or parameter uncertainties. The approach, however, is restricted to a sliding mode control framework. This paper extends this tool to a fairly general class of state feedback control laws, with the stipulation that we know a Lyapunov function for the closed‐loop system. Asymptotic regulation with improvement in transient response is done by using the Lyapunov redesign technique to implement the state feedback control as a saturated high‐gain feedback and introducing a conditional integrator to provide integral action inside a boundary layer. Improvement in the transient response using conditional integrators is demonstrated with an experimental application to the pendubot. Copyright © 2005 John Wiley & Sons, Ltd.     

Fracture and flexural characterization of SiCw/SiC composites at room and elevated temperatures

The fracture and flexural behaviour of monolithic SiC and SiC-whisker reinforced SiC composites (SiC_w/SiC) has been investigated at room and elevated temperatures. Flexure and fracture tests were conducted in a four-point beam configuration at 23 °C, 800 °C and 1200 °C to study the effects of whisker reinforcements especially in respect of mechanical and thermal stability at high energy environments. Flexural strengths and fracture toughness data within the test temperature range are presented in graphical as well as in Weibull form, and experimental observations are analysed and discussed. Increase in flexural strength as well as in fracture toughness has been observed with the whisker reinforcement. However, it was found that the trend discontinues after a certain range of temperature. Post-failure analyses have been performed with the scanning electron microscope (SEM). Formation of glass phase has been observed at the whisker/matrix interface and the crack growth was found to be shifting from intergranular to transgranular with the rise in temperature. Effects of whisker reinforcement and the degradation of flexural and fracture properties at elevated temperature are investigated. Ultrasonic velocity measurements have been performed through the thickness of the untested as well as fractured specimen, and the variation in the sonic wave velocity is discussed in this paper.     

Structural analysis of peptide substrates for mucin-type O-glycosylation

The structures of three nine-residue peptide substrates that show differential kinetics of O-linked glycosylation catalyzed by distinct recombinant uridine diphosphate-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltransferases (GalNAc transferases) were investigated by NMR spectroscopy. A combined use of NMR data, molecular modeling techniques, and kinetic data may explain some structural features required for O-glycosylation of these substrates by two GalNAc transferases, GalNAc-T1 and GalNAc-T3. In the proposed model, the formation of an extended backbone structure at the threonine residue to be glycosylated is likely to enhance the O-glycosylation process. The segment of extended structure includes the reactive residue in a beta-like or an inverse gamma-turn conformation and flanking residues in a beta-strand conformation. The hydroxyl group of the threonine to be glycosylated is exposed to solvent, and both the amide proton and carbonyl oxygen of the peptide backbone are exposed to solvent. The exchange rate of the amide proton for the reactive threonine correlated well with substrate efficiency, leading us to hypothesize that this proton may serve as a donor for hydrogen bonding with the active site of the enzyme. The oxygens of the residue to be glycosylated and several flanking residues may also be involved in a set of hydrogen bonds with the GalNAc-T1 and -T3 transferases.     

Intrasplenic venous flow patterns demonstrated by Doppler ultrasound in patients with portal hypertension

The flow pattern in the splenic vein has been previously reported in patients with portal hypertension, but with no reference to the flow within the intrasplenic venous radicles. Using Doppler ultrasound, this study describes the intrasplenic venous flow direction in 176 adult patients with intrahepatic portal hypertension. In our series, a normal flow pattern was maintained in all except four patients (2.3%) who had either reversed or dual venous drainage patterns resulting in trans-splenic portosystemic shunts. These abnormal patterns are Doppler signs of portal hypertension which might be associated with a higher risk of oesophageal variceal bleeding. It is recommended that the intrasplenic venous flow pattern should be assessed before surgical intervention involving the spleen in patients with portal hypertension.     

Passivity and passivity breakdown of zinc anode in alkaline medium

The electrochemical behaviour of zinc in NaOH solutions has been investigated by using potentiodynamic technique and complemented by X-ray analysis. The E/i curves exhibit active, passive and transpassive regions prior to oxygen evolution. The active region displays two anodic peaks. The passivity is due to the Formation of a compact Zn(OH)₂ film on the anode surface. The transpassive region is assigned to the electroformation of ZnO₂. The reverse sweep shows an activation anodic peak and one catholic peak prior to hydrogen evolution. The influence of increasing additives of NaCl, NaBr and Nal on the anodic behaviour of zinc in NaOH solutions has been studied. The halides stimulate the active dissolution of zinc and tend to break down the passive film, leading to pitting corrosion. The aggressiveness of the halide anions towards the stability of the passive film decreases in the order: I^? > Br^? > Cl^?. The susceptibility of zinc anode to pitting corrosion enhances with increasing the halide ion concentration but decreases with increasing both the alkali concentration and the sweep rate.     

Blind Separation of rotating machine signals using Penalized Mutual Information criterion and Minimal Distortion Principle

The Blind Separation problem of convolutive mixtures is addressed in this paper. We have developed a new algorithm based on a penalized mutual information criterion recently introduced in [El Rhabi et al., A penalized mutual information criterion for blind separation of convolutive mixtures, Signal Processing 84 (2004) 1979–1984] and which also allows to choose an optimal separator among an infinite number of valid separators that can extract the source signals in a certain sense according to the Minimal Distortion Principle. So, the minimisation of this criterion is easily done using a direct gradient approach without constraint on the displacements. Thus, our approach allows to restore directly the contribution of the sources to the sensor signals without post-processing as it is usually done. Finally, we illustrate the performances of our algorithm through simulations and on real rotating machine vibration signals.