Robust tracking control of an induction motor

This paper address the tracking control problem of a induction motor driving a mechanical load. Based on the nonlinear dynamics of the induction motor, a robust tracking controller is developed which can compensate for parametric uncertainties and additive bounded disturbances throughout the entire electromechanical system. A uniform ultimate bounded (UUB) result is obtained for the rotor position tracking error. Simulation results with full state measurements and a flux observer are presented to illustrate the effectiveness of the proposed controller.     

Mikrostruktur und Anlaßverhalten aufgedampfter bzw. thermisch gespritzter ZrO2-Schichten auf metallischen Substraten

Microstructure and Tempering Behaviour of Evaporated resp. Thermally Sprayed ZrO₂-Layers on Metallic Substrates Because of their application in gas turbines plasmasprayed thermal barrier coatings of partially stabilized zirconia on metallic substrates are an example for the technical use of ceramic-metal-composites. Problems especially concerning the interface adhesion are still partly not understood. In this paper several systems are examined by electron microscopy, which all consist of ceramic zirconia layers evaporated or thermally sprayed on a metallic substrate. Priority is given to structural analysis. An attempt is made to lighten the interface morphology by the method of cross section preparing, because thereby the possibility of aimed preparation is given.     

The glass transition temperature of nitrated polystyrene/poly(acrylic acid) blends

Low-molecular-weight polystyrene was nitrated to different levels. The nitrated polystyrene was blended with different molecular weights of poly(acrylic acid), PAA. The glass transition temperatures (T_g) for the mixtures were investigated by differential scanning calorimetry. A single T_g was observed for all blends, indicating single-phase blends. In general, it was found that the T_g increases with molecular weight of PAA. The T_g values of the blends showed a positive deviation from the linear average T_g as a result of strong hydrogen bonding between the segments of the component polymers. The observed T_g values were not adequately represented by simple predictive equations or by single-parameter fitting equations. However, two-parameter fitting equations gave a reasonable representation of the data.     

Fractionation of Starch Amylopectin and Amylose by High Performance Gel Filtration Chromatography

A gel filtration chromatographic method has been developed which is capable of fractionating amylose and amylopectin in starch. Three GFC columns (2 × 4000 A and 1 × 300A PL Separation Sciences, Polymer Laboratories Ltd,) are used in series using sodium chloride solution as eluent. Minimal sample preparation is involved which includes a preliminary wetting of powder starch with ethanol followed by dissolution with sodium hydroxide. Since the solvent system is aqueous, cooked starch samples are analysed by direct dissolution with sodium hydroxide. The method shows promise as a rapid technique in elucidating starch structure.     

A study of the influence of lanthanum fluoride on the tribological properties of bonded solid film lubricants and its mechanism of function

The influence of lanthanum fluoride (LaF₃) on the characteristics of phenolepoxy-bonded MoS₂ dry films was investigated. The functional mechanism was specifically studied using several analytical means. The results showed that the wear life of dry films containing a certain amount of LaF₃ was considerably increased over that of the films without LaF₃. However, the effect of LaF₃ on the friction coefficient of the dry films was shown to be negligible. It was found that the addition of LaF₃ is effective in reducing the oxidation tendency of MoS₂ in the films during the friction process. The reason for this is investigated by the authors.     

Morphological Study of Products Containing β-Cyclodextrin

β-Cyclodextrin (β-CD) has been applied in various fields of drug formulation. Its presence in powder Paracetamol (PAR) products prepared with different methods (kneading and spray drying) changes the morphology of original drug. The product made by spray drying has nearly isodimensional spherical particles, and potentially better flowability than the kneaded product. Spray drying of PAR product without β-CD shows similar morphology like a product with β-CD, but the particles show a greater inclination to adhesion. The results were obtained by electron microscopic study.     

Simultaneous interpenetrating networks for tough matrix composites

Graphite fiber reinforced epoxy composites normally exhibit low impact strength, poor delamination resistance, and low damage tolerance. Because delamination is a matrix-dominated failure mode, tougher matrix resins may be utilized to reduce or eliminate the adverse effects of delamination on the structural integrity of fiber composites. The effects of modifying epoxy network morphology by introducing polyurethane in the form of an interpentrating network were studied. The compatibility, toughness, and tensile properties of the matrix as well as the properties of the resultant laminates were evaluated. One of the conclusions arising was that the interpenetrating network morphology results in superior resin and composites toughness with increasing polyurethane content. However, the benefits of increased resin toughness did not necessarily translate into proportionally increased composite owing to the geomertical limitations placed on the plastic deformation zones in laminates.     

Preparation,Characterisation, and Rheological Behaviour of Starch-Sodium Trimetaphosphate Hydrogels

Ionic biopolymer hydrogels were prepared by the cross-linking of starches with sodium trimetaphosphate in alkaline medium at 40°C for 2 hours. The swelling capacity is relatively high — up to 310 g H₂0/g polymer. Salt solutions have a marked influence, and result in shrinkage but not in a total collapse. The effect of both the cross-linker and substrate concentrations on the swelling and rheological properties was investigated. The influence of temperature and NaOH concentration on the rheological behaviour suggests that they are both significant in determining the gel properties because of the readiness of the diester phosphate bonds to undergo hydrolysis. The molecular weight between two entanglement points (M_e) and the effectiveness of cross-linking [n_e(r)/n_e(t)] were estimated from the observed G_p′ values, and those calculated from complete conversion of the cross-linker. The effectiveness of cross-linking lay between 0.2 and 2.74% for 10% wlw gels, and reached a maximum of 48.1% at the higher substrate concentration of 20% wlw. ¹³C-NMR signals from the anhydroglucose units became broader and decreased in intensity with rising cross-linker concentration due to the restricted motion arising from the additional bonding.     

Thermal properties,phase transitions,and morphology of a conjugated polymer

A highly conjugated polymer was synthesized from α,α′-dibromo-p-xylene, 1,4-bis(2-hydroxy-benzoyl)benzene, and benzyl bromide via a modified Williamson ether synthesis under phase transfer conditions. Based on thermal analysis, polarized light microscopy, electron diffraction, and wide angle X-ray diffraction experiments, the heat capacities in the solid and liquid states have been determined. The glass transition temperature is at 358 K with a heat capacity increase of 164 J/(K mol). Two different ordered crystal forms with different crystal unit cells were observed. The more ordered crystal shows a low transition temperature and the less ordered one a high transition temperature. This is mainly due to the effect of entropy change. These crystals exhibit various crystal morphologies with different birefringences. Transition kinetics are expressed by an Avrami equation. Two crystals show different Avrami exponents with crystallization temperature, which corrspond to the morphological change. Competition between crystal growths is also discussed.