1,721,016 research outputs found
Annular Stochastic Finite-Time Stability Using Piecewise Quadratic Lyapunov Functions
No full textIn this paper we present some new sufficient conditions for the annular stochastic finite-time stability of a class of stochastic linear time-varying systems. These new conditions are obtained adopting time-varying piecewise quadratic Lyapunov functions rather than the classical quadratic ones. The proposed approach allows us to extend the class of consider domains, which are typically limited to ellipsoidal domains. The proposed finite-time stability conditions can be converted into a feasibility problem based on a set of differential linear matrix inequalities. Two numerical examples are considered to perform a comparison with the previous results, and they show that the new proposed conditions are less conservative than the previous ones
Conditions for annular finite-time stability of Itô stochastic linear time-varing systems with Markov switching
No full textIn this study, the authors tackle some control problems related to the class of continuous-time, stochastic linear time-varying systems with Markov switching. First, the annular stochastic finite-time stability problem is considered, and two sufficient conditions are derived by considering the Itô formalism. Both conditions require the solution of a feasibility problem based on differential linear matrix inequalities. The former turns out to be less conservative and, therefore, is exploited in the analysis context; however, it cannot be converted into a computationally tractable condition for feedback purposes. The latter, which is based on a more conservative assumption, allows us to solve the state-feedback design problem. They show that the proposed approach obtains less conservative results with respect to the previous literature. Moreover, the application of the methodology to the finite-time control of a satellite illustrates the effectiveness of the proposed approach when facing engineering problems
Thermal and combustion behaviour of layered silicate-epoxy nanocomposites
No full textThe present research looks at the thermal properties of epoxyeclay nanocomposites synthesised by in situ polymerisation of a prepolymer (diglycidyl ether of bisphenol-A) crosslinked with methyl tetrahydrophthalic anhydride. The inorganic phase was montmorillonite, exchanged with alkylammonium ions in order to give organophilic properties to the phyllosilicate. The morphology of epoxyemontmorillonite nanocomposites examined by X-ray diffraction and transmission electron microscopy shows that mixed delamination or intercalation or microdispersion can occur depending on type of organoclay. Thermogravimetric analysis shows that in nanocomposites the epoxy matrix is sheltered from the action of oxygen. Cone calorimeter tests show that the rate of heat release in the nanocomposite combustion is strongly reduced
Heterogeneity of the zona pellucida carbohydrate distribution in human oocytes failing to fertilize in vitro.
No full textRadiation curing of dyacrylate glycerolate of bisphenol-A in the presence of an organically modified montmorillonite for the production of flame resistant polymer-clay composites
No full textPolymerization of an acrylate derivative of bisphenol-A by ionizing radiation in the presence of an organically modified montmorillonite was carried out in order to produce a flame-retardant composite. The measurement of the thermal effect during irradiation indicates that radiation curing of pure resin and resin-clay mixtures occurred in both cases. Moreover, differential scanning calorimetry and dynamic mechanical thermal analysis showed that a curing completion can be obtained by thermal curing after irradiation with a significant increase of the glass transition temperature. The morphology was investigated by X-ray diffraction and transmission electron microscopy. These have indicated that gamma irradiation leads to the formation of a microcomposite structure after radiation curing. The flame resistant characteristics were studied by means of thermal gravimetric analysis under nitrogen and air and by cone calorimeter tests. In particular, thermal gravimetric analysis in air showed that the presence of the dispersed clay in the polymer matrix increases the oxidation temperature. This is attributed to the formation of a more stable char, due to a protective skin of clay aggregates that builds up on the surface of the volatilizing polymer matrix during thermal degradation which protects the charred polymer from reactions with oxygen. Finally, the cone calorimeter tests show a reduction of heat release of the clay-polymer composite with respect to the neat resin. The contribution of the clay in reducing the rate of heat release is attributed to the dispersion of the filler that allows build-up of an inorganic surface layer at a rate which is sufficient for effectively compete with the feeding of the flame with combustible pyrolysis products
A constrained control framework for unmanned aerial vehicles based on Explicit Reference Governor
No full textThis paper tackles the constrained control problem of unmanned aerial vehicles with planar multirotors. The proposed solution splits the constrained control problem into two separate tasks, i.e. stabilization and constraint enforcement. It is shown that the problems addressed by each individual layer is much simpler than the original combined problem. For the unconstrained control of UAVs we consider a control scheme based on a cascade structure. The Lyapunov function for the stabilized cascaded system is then derived. Using this Lyapunov function, we develop an Explicit Reference Governor for constraint enforcement. Numerical simulation shows the effectiveness of the proposed approach
Heterogeneity of the zona pellucida carbohydrate distribution in human oocytes failing to fertilize in vitro
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