Shape and topology optimization for periodic problems

The present paper deals with the implementation of an optimization algorithm for periodic problems which alternates shape and topology optimization; the theoretical background about shape and topological derivatives was developed in Part I (Barbarosie and Toader, Struct Multidiscipl Optim, 2009). The proposed numerical code relies on a special implementation of the periodicity conditions based on differential geometry concepts: periodic functions are viewed as functions defined on a torus. Moreover the notion of periodicity is extended and cases where the periodicity cell is a general parallelogram are admissible. This approach can be adapted to other frameworks (e.g. Bloch waves or fluid dynamics). The numerical method was tested for the design of periodic microstructures. Several examples of optimal microstructures are given for bulk modulus maximization, maximization of rigidity for shear response, maximization of rigidity in a prescribed direction, minimization of the Poisson coefficient.     

Iterative algorithm to compute the maximal and stabilising solutions of a general class of discrete-time Riccati-type equations

In this article an iterative method to compute the maximal solution and the stabilising solution, respectively, of a wide class of discrete-time nonlinear equations on the linear space of symmetric matrices is proposed. The class of discrete-time nonlinear equations under consideration contains, as special cases, different types of discrete-time Riccati equations involved in various control problems for discrete-time stochastic systems. This article may be viewed as an addendum of the work of Dragan and Morozan (Dragan, V. and Morozan, T. (2009), ‘A Class of Discrete Time Generalized Riccati Equations’, Journal of Difference Equations and Applications, first published on 11 December 2009 (iFirst), doi: 10.1080/10236190802389381) where necessary and sufficient conditions for the existence of the maximal solution and stabilising solution of this kind of discrete-time nonlinear equations are given. The aim of this article is to provide a procedure for numerical computation of the maximal solution and the stabilising solution, respectively, simpler than the method based on the Newton–Kantorovich algorithm.     

Analysis of methanol–ethanol mixtures from falsified beverages using a dual biosensors amperometric system based on alcohol dehydrogenase and alcohol oxidase

A portable bienzymatic analytical system was developed for the chronoamperometric analysis of methanol–ethanol mixtures. The system consists of two biosensors, one based on alcohol dehydrogenase (ADH) that responds only to the ethanol and the second one based on alcohol oxidase (AOX) that responds to both methanol and ethanol. The transducers were screen-printed electrodes (SPEs) modified with mediators: Meldola blue for ADH and Co-phthalocyanine for AOX. The calibration graph of the ADH biosensor is linear between 0.3 and 8 mmol/L ethanol. The AOX biosensor is able to quantify both analytes in mixtures that contain methanol between 3 and 70 mmol/L and ethanol ranging from 15 to 110 mmol/L. Interferences due to non-specific oxidations from common oxidizable compounds like gallic acid and ascorbic acid were smaller in the case of transducer based on Meldola blue. The analytical system was successfully tested on real samples: non-alcoholised beer (NAB) spiked with ethanol or methanol and a falsified rose wine (FRW).     

Insights Into Molecular Interaction of Antitumor Drug Mitoxantrone With Anionic Surfactant Sodium Dodecyl Sulfate at Different Temperatures

A study of the interaction of antitumor drug mitoxantrone with anionic surfactant sodium dodecyl sulfate (SDS) has been carried out by UV–Vis absorption spectroscopy at submicellar and micellar surfactant concentrations, pH 7.4 and 10, and over a temperature range of 293.15–323.15 K. The variation of the monomer drug absorbance as a function of SDS concentration indicates, at pH 7.4 and all investigated temperatures, two definite processes: process I in the submicellar range, attributed to the electrostatic interaction between mitoxantrone and SDS monomers; and process II in the micellar range, when the drug is incorporated into SDS micelles in monomer form. At pH 10, the results have indicated only the process II at micellar SDS concentrations. The monomer absorbance changes occurring as a result of the interactions between mitoxantrone and SDS were rationalized in terms of binding constant, micelle/water partition coefficient, and the corresponding thermodynamic parameters for binding and partitioning processes. Thermodynamic parameters indicate that at pH 7.4 both binding process of mitoxantrone to SDS and partition process of mitoxantrone between micellar and bulk aqueous phases are spontaneous and enthalpy controlled, while at pH 10 both processes are spontaneous and entropy controlled.     

Output‐based H2 optimal controllers for a class of discrete‐time stochastic linear systems with periodic coefficients

The aim of the paper is to present a design procedure of the optimal controller minimizing the H₂‐type norm of discrete‐time stochastic linear systems with periodic coefficients simultaneously affected by a nonhomogeneous but periodic Markov chain and state and control multiplicative white noise perturbations. Firstly, two H₂‐type norms for the linear stochastic systems under consideration were introduced. These H₂‐type norms may be viewed as measures of the effect of the additive white noise perturbations on the regulated output of the considered system. Before deriving of the state space representation of the optimal controller, some useful formulae of the two H₂‐type norms were obtained. These formulae are expressed in terms of periodic solutions of some suitable linear equations and are derived in the absence of some additional assumptions regarding the Markov chain other than the periodicity of the sequence of the transition probability matrices. Further, it is shown that the optimal H₂ controller depends on the stabilizing solutions of some specific systems of coupled Riccati equations, which generalize the well‐known control and filtering equations from linear time invariant case. For the readers convenience, the paper presents iterative numerical algorithms for the computations of the stabilizing solutions of these Riccati type systems. The theoretical developments are illustrated by numerical examples. Copyright © 2014 John Wiley & Sons, Ltd.     

New polyurea MWCNTs nanocomposite films with enhanced mechanical properties

Polyurea nanocomposites represent a promising option in the development of advanced materials for applications that require high mechanical resistance. This article describes an optimized synthetic route for obtaining polyurea nanocomposites with enhanced mechanical properties by employing epoxy‐functionalized multiwalled carbon nanotubes (MWCNTs) as reinforcing agent. The experimental measurements revealed that these functionalized nanofillers have a positive effect on the properties of the composite only until they reach a certain concentration; therefore, the optimal composition was reported (the samples containing 0.2 weight % functionalized MWCNTs). The functionalization of the MWCNTs was confirmed through RAMAN, X‐ray photoelectron spectroscopy, scanning electron microscopy and thermogravimetric analysis, while the polyurea nanocomposites obtained have been characterized by thermal (differential scanning calorimetry and TGA) and mechanical (dynamic mechanical analysis and tensile tests) analyses. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45061.     

H 2 optimal control for a wide class of discrete-time linear stochastic systems

In this article, the problem of H ₂-control of a discrete-time linear system subject to Markovian jumping and independent random perturbations is considered. Different H ₂ performance criteria (often called H ₂-norms) are introduced and characterised via solutions of some suitable linear equations on certain spaces of symmetric matrices. Some aspects specific to the discrete-time framework are revealed. The problem of optimisation of H ₂-norms is solved under the assumption that full state vector is available for measurements. One shows that among all stabilising controllers of higher dimension, the best performance is achieved by a zero-order controller. The corresponding feedback gain of the optimal controller is constructed based on the stabilising solution of a system of discrete-time generalised Riccati equations.     

The linear quadratic optimization problems for a class of linear stochastic systems with multiplicative white noise and Markovian jumping

In this paper, the linear quadratic optimization problem for a class of linear stochastic systems subject both to multiplicative white noise and Markovian jumping is investigated. Two classes of admissible controls are considered. One of these classes contains controls with additional property that corresponding trajectories tend to zero (in mean square) when tends to /spl infin/, while concerning the controls contained in the second class of admissible controls there is not any stability assumption. In the optimization problem over the first class of admissible controls, the cost functional could have indefinite sign of weights matrices. An iterative procedure to compute the maximal solution of the systems of generalized Riccati equations is provided. A numerical example to illustrate the applicability of the iterative procedure is given.     

Redox behavior of hemin at p-GaAs(1 0 0) electrode

Electrochemical behavior of hemin on p-GaAs(1 0 0) electrodes was examined by cyclic voltammetry (CV) and impedance spectroscopy (EIS) in phosphate buffer solutions (PBS) at pH 7.45. CV investigations in 0.6 mM hemin in PBS revealed a pair of reversible peaks at −0.44 and −0.32 V vs. SCE resulting in stable adsorbed species. EIS spectra analysis pointed out that these adsorbed species bring significant changes in the semiconductor surface state population and the potential drop distribution between the semiconductor space charge region and the Helmholtz layer.