Potential and limitations of a teleteaching environment based on H.323 audio-visual communication systems

The effective support of teleteaching services requires the development of multimedia collaboration systems that are capable of providing real-time and high quality audio-visual communication among distributed instructors and students. In the absence of such specialised systems, technologies tailored to other services are being considered for teleteaching services as well. Such a technology is the H.323 audio-visual communication technology developed to support video communication over IP. Although teleteaching and videoconferencing have similar QoS requirements, teleteaching functional requirements are a superset of those of videoconferencing. In this paper, the suitability of H.323 technology and currently available products to support teleteaching services is investigated, based on experience gained during a related deployment at the University of Athens.     

Robust model predictive control for optimal continuous drug administration

In this paper the model predictive control (MPC) technology is used for tackling the optimal drug administration problem. The important advantage of MPC compared to other control technologies is that it explicitly takes into account the constraints of the system. In particular, for drug treatments of living organisms, MPC can guarantee satisfaction of the minimum toxic concentration (MTC) constraints. A whole-body physiologically-based pharmacokinetic (PBPK) model serves as the dynamic prediction model of the system after it is formulated as a discrete-time state-space model. Only plasma measurements are assumed to be measured on-line. The rest of the states (drug concentrations in other organs and tissues) are estimated in real time by designing an artificial observer. The complete system (observer and MPC controller) is able to drive the drug concentration to the desired levels at the organs of interest, while satisfying the imposed constraints, even in the presence of modelling errors, disturbances and noise.     

First‐mover advantages of the European Union's climate change mitigation strategy

This paper assesses the costs and benefits for the European Union (EU) as a first mover in climate change mitigation. Scenarios of EU and global climate action to 2050 are quantified using the GEME3‐RD model, a global multi‐sectoral computable general equilibrium model with endogenous technology progress and detailed representation of the clean energy technologies. The model includes two‐factor learning curves (stock and research and development funding) for clean energy technologies, such as electric vehicles, carbon capture and storage, and renewable and efficient appliances. Funding of research and development is endogenously derived as a production factor enabling productivity improvement. The scenarios compare stylised climate strategies, which are asymmetric by world region and have different emission reduction profiles over time. Assuming that strong climate mitigation action will be undertaken only after 2030, the scenarios compare two main strategies for the EU: pursuing strong emission reduction unilaterally until 2030 versus deferring action for the period after 2030. Asymmetric climate action by region enables asymmetric innovation and manufacturing of clean energy technologies. The macroeconomic assessment of the climate action strategies does not only depend on costs of clean technologies but also on induced technology progress implying asymmetric effects on manufacturing and trade by region, taking into account spillovers. The model‐based projections show clear advantages for the EU as a first mover in climate change mitigation compared with a delaying of climate action until 2030. Delayed climate action until 2030 implies higher gross domestic product losses for the EU compared with unilateral action until 2030. The model finds benefits of early action by the EU driven by activity and progress related to clean energy technologies as the EU can achieve competitive advantages over other world regions pursuing climate action later. Copyright © 2016 John Wiley & Sons, Ltd.     

Simulation of piston ring tribology with surface texturing for internal combustion engines

Design of piston rings is a very crucial subject in the field of internal combustion engines. In the present paper, a numerical model is created using the Navier–Stokes equations. Fluid–structure interaction analysis is performed in order to calculate the structural integrity of the ring for several engine operational conditions and texturing patterns. This paper illustrates the hydrodynamic friction force under various surface artificial texturing in terms of spherical and rectangular microdimples. Piston ring stress analysis is also investigated due to gas leakage. Results show a substantial reduction of the friction using rectangular texturing and less reduction using spherical texturing. The rectangular microdimple parameters were considered to obtain a better friction reduction with the following configurations: H_d = 4 µm, ρ_τ = 0.61, λ = 20 and s = 0.004. Each rectangular texture cell is defined by the dimple depth, H_d; the texture density, ρ_τ; the dimple aspect ratio, λ; and the relative dimple depth, s. Copyright © 2014 John Wiley & Sons, Ltd.     

Study of Al2O3 coatings on AISI 316 stainless steel obtained by controlled atmosphere plasma spraying (CAPS)

The tribological behaviour of Al₂O₃ coatings on AISI 316 stainless steel, obtained by the process of controlled atmosphere plasma spraying (CAPS), is studied in this work. Atmospheric plasma spraying (APS) and high pressure plasma spraying (HPPS) were applied in order to produce these coatings. The APS coatings exhibited lower microhardness values compared to the values of HPPS coatings. Regarding the HPPS coatings it was found that plasma composition, through its heat capacity, does influence the heat transfer to particles, and, consequently, their flattening and densification process, which govern coating properties. It was revealed that tribological behaviour of coatings was influenced by the applied spraying method too. Coatings from HPPS under high-enthalpy conditions led to worst wear behaviour. In general, properties, such as microstructure, microhardness, coefficient of friction and wear resistance depended on the processing conditions such as pressure and composition of the spraying chamber atmosphere.     

Multimodal genetic algorithms-based algorithm for automatic point correspondence

In this paper, the problem of automatic determination of point correspondence between two images is formulated as a multimodal function optimization and the usefulness of genetic algorithms (GAs) as a multimodal optimizer is explored. Initially, a number of variations of GAs, capable of simultaneously discovering multiple extremes of an objective function are evaluated on a mathematical benchmark objective function with multiple unequal maxima. The variation of the GAs that performs best on the benchmark function, in terms of the number of maxima discovered, is selected for the determination of automatic point correspondence between two images. The selected variation of the GAs involves an iterative procedure for the formation of a genetic population of individuals (or chromosomes). Each individual encodes the position of a point of interest on one of the available images as well as parameters of a local transformation that generates the position of the corresponding point on the other image. The proposed algorithm aims to discover individuals that corresponds to local maxima of an objective function that measures the similarity between patches of the two images. When the GAs-based multimodal optimization algorithm terminates, pairs of corresponding points between the two images are obtained that can be used for the generation of a dense deformation field by means of the thin plate splines model.The proposed algorithm is applied to 2D medical images (dental and retinal images) under known transformations (similarity and elastic transformation) and is also assessed on medical images with unknown transformations (computer tomography transverse slices). The proposed algorithm is compared against the iterative closest point (ICP) algorithm, and a well-known non-rigid registration algorithm, based on free-form deformations (FFD) using various quantitative criteria. The obtained results indicate that in case of known similarity transformations, the proposed multimodal GAs-based algorithm and the ICP algorithm present equivalent performance, whereas the FFD algorithm is clearly outperformed. In the case of known sinousoidal deformations, the proposed multimodal GAs-based and the FFD algorithm achieve equivalent performance and clearly outperform the ICP algorithm. Finally, in the case of unknown elastic deformations, the proposed GAs-based algorithm appears to perform marginally better than the FFD algorithm, whereas it clearly outperforms the ICP algorithm.     

Rust morphology characterization of polyurethane and acrylic-based marine antifouling paints after salt spray test on scribed specimens

A newly developed, polyurethane-based, marine antifouling coating, containing 2% immobilized Econea, was examined in terms of its anticorrosion performance. The novelty of the experimental formulation arises from the immobilization of the biocide which minimizes leaching and was accomplished via a newly developed functionalization method, based on reaction of the biocide with highly reactive isocyanate functionality. The painting system was applied on steel specimens, then scribed with a sharp cutter and examined for 12 weeks in cyclic salt spray exposure. Identification of the rust morphologies was performed with XRD, Raman spectroscopy, SEM, and EDS methods. The absence of paint deformation during the experiment led to the formation of compact corrosion products, firmly adherent to the substrate, allowing transformation to more protective forms, such as oxides (hematite, maghemite, magnetite) and the least harmful of the oxyhydroxides (goethite, feroxyhyte), found in the mixture, ensuring sufficient corrosion protection. The unscratched part of the paint served as a barrier to corrosion product expansion beyond the scribed areas. An acrylic-based antifouling system was also examined for reasons of comparison. The experimental formulation exhibited superior anticorrosion performance overall, since the acrylic system presented extended material loss, blistering, checking, and extensive substrate rust coverage beneath the multilayer coat, implying unsatisfactory corrosion protection.     

Cavitation effects on textured compression rings in mixed lubrication

Thin lubricant films and cavitation to ring–bore contact have a directly correlation between wear and emissions output of internal combustion engines. Thus, there is a need to develop innovate engineering solutions such as surface texturing. In particular, micro textures are manufactured in order to keep more lubricant in weakly lubricated contact. An isothermal mixed‐hydrodynamic analysis was developed for textured compression rings, which utilised the effects of two‐phase flow using Navier–Stokes equations, vapour transport and asperity interaction. Realistic boundary conditions are used from a real motorbike engine. This paper employs a computational model including multiphase flow of the ring–bore conjunction in order to predict the effects of surface texturing of the barrel face ring around the dead centres. The model is validated using numerical and experimental results from the literature. Additionally, flow simulations have been performed, on how micro‐dimples shape and depth on the ring liner affect on the total friction and minimum lubricant film. Copyright © 2016 John Wiley & Sons, Ltd.