Optimal systems for equipment maintenance and replacement under Markovian deterioration

Deterioration of equipment is modeled as a multistate discrete time controlled Markov process. The states are classified according to the degree of deterioration. The problem of design of optimal systems for equipment maintenance and replacement is considered when the decision-maker may take, in each stage, one of many available maintenance actions, classified according to their “stochastic effectiveness”; no action and replacement are included as alternatives. It is assumed that the transition probabilities satisfy two conditions which effectively describe a trend for monotonically increasing expected deterioration and rate of deterioration. Under these assumptions it is proved in the paper that the optimal (cost minimizing) decision system in an infinite horizon is of the control limit rule type, rapidly obtained by policy improvement algorithms. A numerical example is presented for a specific practical application; detailed data are available from the authors on request.     

On comparing optimum Alternating Direction Preconditioning and Extrapolated Alternating Direction Implicit schemes

The purpose of this paper is to show the equivalence of Alternating Direction Preconditioning and Extrapolated Alternating Direction Implicit methods in the case of two-level one-parameter optimized schemes as far as convergence rates are concerned, and also to give optimum parameters for the numerical solution of the self-adjoint second-order elliptic partial differential equation and the biharmonic equation.     

Rapid Microwave-Assisted Synthesis of CdS/Graphene/MoSx Tunable Heterojunctions and Their Application in Photocatalysis

Nanoscale two-dimensional nanostructures have shown great potential as functional components in photocatalysis. Here, investigations on the synthesis of heterostructured hybrids, comprised of 0D CdS nanoparticles as semiconductor and 2D/2D graphene/MoS_x as co-catalyst, are reported. The approach involves a rapid microwave-assisted reaction in autoclave conditions, by adopting either a one-step or a two-step protocol. The chemical speciation of the nanocomposites was found to depend strongly on the compounding conditions of the precursor substances. The photocatalytic activity was assessed by monitoring the photodegradation rate of 4-nitrophenol in solution using simulated solar light irradiation. The photocatalytic activity of the hybrids may be attributed to a combination of beneficial characteristics, strongly related to the chemical speciation of the composite components. Moreover, intimate contacts of the latter result in efficient heterojunctions. Overall, the present study provides valuable insight into the development of functional heterostructured photocatalysts comprised of two-dimensional nanomaterials.     

Synthesis,characterization and self‐assembly of well‐defined linear heptablock quaterpolymers

Two well‐defined heptablock quaterpolymers of the ABCDCBA type [Α: polystyrene (PS), B: poly(butadiene) with ～90% 1,4‐microstructure (PB_1,4), C: poly(isoprene) with ～55% 3,4‐microstructure (PI_3,4) and D: poly(dimethylsiloxane) (PDMS)] were synthesized by combining anionic polymerization high vacuum techniques and hydrosilylation/chlorosilane chemistry. All intermediates and final products were characterized by size exclusion chromatography, membrane osmometry, and proton nuclear magnetic resonance spectroscopy. Fourier transform infrared spectroscopy was used to further verify the chemical modification reaction of the difunctional PDMS. The self‐assembly in bulk of these novel heptablock quarterpolymers, studied by transmission electron microscopy and small angle X‐ray scattering, revealed 3‐phase 4‐layer alternating lamellae morphology of PS, PB_1,4, and mixed PI_3,4/PDMS domains. Differential scanning calorimetry was used to further confirm the miscibility of PI_3,4 and PDMS blocks. It is the first time that PDMS is the central segment in such multiblock polymers (≥3 chemically different blocks). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1443–1449     

PI-b-PMMA diblock copolymers: nanostructure development in thin films and nanostructuring of thermosetting epoxy systems

Poly(isoprene-block-methyl methacrylate) (PI-b-PMMA) block copolymers with different block ratios have been used to generate nanostructures both in thin films and by nanostructuring a thermosetting epoxy system. Obtained morphologies have been analyzed in terms of atomic force microscopy. The nanostructuring of thin films was carried out by thermal and solvent vapor annealing, in which the copolymer films were exposed to acetone vapors, selective solvent for methyl methacrylate (PMMA) block. By solvent vapor annealing thin films of both copolymers self-assembled into a hexagonally packed cylindrical morphology. Thermal annealing was carried out above the glass transition temperature of both blocks, obtaining worm-like and lamellar morphologies, depending on the block ratio. One of the copolymers has also been used for nanostructuring an epoxy thermosetting system. Morphologies consisting of spherical-shaped PI domains dispersed in a continuous epoxy matrix in which PMMA remained miscible were obtained, independently of the copolymer amount.     

Hydration studies in polymer hydrogels

Polymer hydrogels have attracted much interest in recent years based on numerous applications mainly in biotechnology and medicine. For the knowledge‐based design and development of new materials for these and similar applications, it is essential to understand better the hydration properties of hydrogels and of polymers in general. With this term, we mean the particular organization of water in the hydrogel, which determines the properties of the water component, typically different than those of bulk water, and the impact of water on the properties of the polymer matrix itself. In this review, we focus on recent work with hydrogels based on poly(hydroxyethyl acrylate), mostly copolymers with a second hydrophobic polymer and silica nanocomposites. The combination of water sorption/diffusion, thermal and dielectric studies, by fully exploiting the capabilities of each individual technique, proves essential in providing significant information on particular aspects of hydration, such as water uptake, water organization, and diffusion coefficients; glass transition and plasticization; water and polymer dynamics; protonic conductivity, and in revealing interesting correlations between these particular aspects. In the outlook similarities and differences to other related systems, such as protein‐water and polymer solutions in non‐polar solvents, are stressed in the perspective of a broader study. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Facile and Low-Cost SPE Modification Towards Ultra-Sensitive Organophosphorus and Carbamate Pesticide Detection in Olive Oil

Despite the fact that a considerable amount of effort has been invested in the development of biosensors for the detection of pesticides, there is still a lack of a simple and low-cost platform that can reliably and sensitively detect their presence in real samples. Herein, an enzyme-based biosensor for the determination of both carbamate and organophosphorus pesticides is presented that is based on acetylcholinesterase (AChE) immobilized on commercially available screen-printed carbon electrodes (SPEs) modified with carbon black (CB), as a means to enhance their conductivity. Most interestingly, two different methodologies to deposit the enzyme onto the sensor surfaces were followed; strikingly different results were obtained depending on the family of pesticides under investigation. Furthermore, and towards the uniform application of the functionalization layer onto the SPEs’ surfaces, the laser induced forward transfer (LIFT) technique was employed in conjunction with CB functionalization, which allowed a considerable improvement of the sensor’s performance. Under the optimized conditions, the fabricated sensors can effectively detect carbofuran in a linear range from 1.1 × 10^?9 to 2.3 × 10^?8 mol/L, with a limit of detection equal to 0.6 × 10^?9 mol/L and chlorpyrifos in a linear range from 0.7 × 10^?9 up to 1.4 × 10^?8 mol/L and a limit of detection 0.4 × 10^?9 mol/L in buffer. The developed biosensor was also interrogated with olive oil samples, and was able to detect both pesticides at concentrations below 10 ppb, which is the maximum residue limit permitted by the European Food Safety Authority.     

On set theoretic complete intersections in P k 3

We prove that smooth monomial curves of degree greater than three are not set theoretic complete intersections on a wide class of surfaces, called bihonogeneous surfaces.     

The solution of the linear complementarity problem by the matrix analogue of the accelerated overrelaxation iterative method

The Linear Complementarity Problem (LCP), with an H₊?matrix coefficient, is solved by using the new “(Projected) Matrix Analogue of the AOR (MAAOR)” iterative method; this new method constitutes an extension of the “Generalized AOR (GAOR)” iterative method. In this work two sets of convergence intervals of the parameters involved are determined by the theories of “Perron-Frobenius” and of “Regular Splittings”. It is shown that the intervals in question are better than any similar convergence intervals found so far by similar iterative methods. A deeper analysis reveals that the “best” values of the parameters involved are those of the (projected) scalar Gauss-Seidel iterative method. A theoretical comparison of the “best” (projected) Gauss-Seidel and the “best” modulus-based splitting Gauss-Seidel method is in favor of the former method. A number of numerical examples support most of our theoretical findings.