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    ABSTRACT: Cold spraying is an innovative coating technology mainly based on the high speed impact of metals and ceramic particles on different substrates. Through the employment of low temperature gases (Air, He, N2) spray particles (usually 1–50 μm in diameter) are accelerated to a high velocity (typically 300–1200 m/s) that is generated through a convergent–divergent de Laval type nozzle. Severe plastic deformation of particles impacting on the substrate occurs at temperature well below the melting point leading to the unique mechanical properties experienced by such kinds of coatings. In the present paper the main processing parameters affecting the microstructural and mechanical behavior of metal–metal cold spray deposits are described. The effect of processing parameters on grain refinement and mechanical properties were analyzed for different particles (Ti–TiAl3, Al–Al2O3, Ni–Cr3C2, Ni–BN, Cu–Al2O3, Co–SiC). The results belonging to the properties of the formed nanocomposites were compared with those of the pure parent materials sprayed in the same conditions. Many experimental conditions have been analyzed in terms of particle dimensions and composition, substrate temperature and composition, gas temperature and pressure, nozzle properties. In particular, those conditions leading to a strong grain refinement with an acceptable level of the mechanical deposit properties such as porosity, adhesion strength and hardness were underlined.
    Composites Part B Engineering 12/2014; 67:326–331.
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    ABSTRACT: The point-to-point quickest path problem is a classical network optimization problem with numerous applications, including that of computing driving directions. In this paper, we define a lower bound on the time-to-target which is both accurate and fast to compute. We show the potential of this bound by embedding it into an A⁎ algorithm. Computational results on three large European metropolitan road networks, taken from the OpenStreetMap database, show that the new lower bound allows to achieve an average reduction of 14.36%. This speed-up is valuable for a typical web application setting, where a server needs to answer a multitude of quickest path queries at the same time. Even greater computing time reductions (up to 28.06%) are obtained when computing paths in areas with moderate speeds, e.g. historical city centers.
    Computers & Operations Research 10/2014;
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    ABSTRACT: Nanocrystalline TiO2–Diatomite composites (DT) were prepared by depositing TiO2 nanoparticles on the surface of diatomite microparticles. Thermal hydrolysis of titanium oxysulfate in aqueous suspension of diatomites led to the formation of uniform layer of TiO2 on diatomite. The degree of crystallinity of TiO2 nanoparticles was increased with thermal annealing as revealed by xrd analyses. SEM images of the composite samples show uniform layer of TiO2 is successfully deposited on diatomite surfaces. N2 physical adsorption-desorption measurements show higher specific surface area of the composite sample compared to unsupported TiO2. The photocatalytic activity of the composite samples annealed at different temperatures was evaluated by the degradation of Rhodamine B (RhB) dye in aqueous solution under UV-light irradiation and compared with the unsupported TiO2 powders. It is found that the photocatalytic reaction follow a pseudo-first-order rate law and the composite catalyst crystallized at 500 °C shows the highest catalytic activity toward RhB degradation. It was observed that diatomite substrate significantly enhanced the photodegradation efficiency of TiO2 due to higher surface area, mesoporous structure and uniform deposition of the small sized TiO2 particles.
    Applied Catalysis A General 08/2014;
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    ABSTRACT: The implantation of 1 MeV 63Cu+ ions in polycarbonate (PC) matrices has been carried out in order to evaluate the morphological and structural modifications induced in the polymer as a function of the ion fluence in the range 5 × 1013 ions cm−2 to 1 × 1017 ions cm−2. Atomic Force Microscopy analysis reveals a significant roughness increase of the polymer surface only for fluences higher than 5 × 1016 ions cm−2 with the presence of hillock structures which surface density increases with increasing the ion fluence. X-ray Diffraction measurements of PC implanted with fluences in the range between 5 × 1015 at cm−2 and 5 × 1016 at cm−2 reveal an increase of the disorder inside the PC matrix, as a consequence of the damaging process induced by the ion irradiation. Evidences about the presence of exotic phase structures ascribed to both cubic Cu2O and cubic Cu have been found.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 07/2014; 331:187.
  • Progress in Organic Coatings 04/2014; 77(4):803–812.
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    ABSTRACT: This paper is aimed to study the suitability of poly-lactic acid (PLLA) for the production of components by rotational molding. To this purpose, the sintering behavior of PLLA powders was studied by thermomechanical analysis (TMA), in order to identify the onset and endset temperatures of sintering and the onset temperatures of degradation. The results indicate that sintering of PLLA is characterized by two different steps, namely powder coalescence and void removal. The first process is fast, occurring just above the melting temperature, whereas the second one occurs at much higher temperatures. Finally, at higher temperatures, degradation involves the formation of gas in the bulk of the polymer, leading to a decrease of the bulk density. The different phenomena occurring during heating of PLLA powders were interpreted by means of dimensionless numbers. The use of such approach allowed identifying the processing window for PLLA powders, defined as the difference between the endset of sintering and the onset of degradation. In agreement with experimental results, the dimensionless analysis confirmed that wider processing windows are obtained for slower heating rates of PLLA powders. On the other hand, it is well known that potential materials for rotational molding should be characterized by an adequate toughness, essentially related to de-molding of parts. Therefore, PLLA was mixed with two different plasticizers, a non-biodegradable one, i.e. di-ethyl-hexyl-phthalate (DEHP) and a biodegradable one, i.e. poly-ethylene glycol (PEG). The plasticizers were responsible of a reduction of viscosity and therefore a faster sintering process. On the other hand, the decrease of thermal stability due to the addition of plasticizer is expected to significantly decrease the width of the processing window.
    Thermochimica Acta 04/2014;
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    ABSTRACT: Over the last decades, the production of “sustainable energy” has provided a very fertile research field, involving aspects that are traditionally considered in an independent manner, namely renewable energy production, energy storage and efficient usage of available energy. A combined analysis of these three aspects within an industrial context is the main focus of this work. We provide an insight on the problems that a small or medium manufacturing firm can expect to address when it decides to move from traditional energy suppliers to an as much as possible autonomous energy production. In particular, we consider the contribution that ICT can offer in order to allow the firm to decide the best size and composition of its own “energy production plant”, based on data regarding its production needs and weather-related data. We propose an open source framework aimed at making it possible to model various systems including both energy production, storage and consumption elements. The framework also allows the use of different approaches to optimize and fine tune the system in terms of both design and usage costs. We show how the framework can be specialized in order to be used for a typical industrial test case representing a small medium manufacturing firm that decides to change its position from a pure energy consumer to an energy combined producer, storer and user.
    Computers in Industry 04/2014;
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    ABSTRACT: The importance of historical buildings preservation is constantly increasing due to damage concerns to cultural property. In these buildings, the indoor conditions should be carefully evaluated with the priority of conservation. If adequate, a natural microclimate, to which artworks have been adapted over centuries, should be maintained avoiding sudden microclimatic changes and taking into account the main features of the site. A three dimensional (3D) computational fluid-dynamics (CFD) model was developed to investigate the adequacy of natural ventilation in an historical building located in the South of Italy. The model was validated with experimental data to analyze the microclimatic conditions obtained inside the building by five ventilation scenarios and twenty computational models. The aim of the study was to find the solution able to provide a proper microclimate for the conservation of the building. Wind direction influence was considered in opposite seasonal conditions, and the microclimatic variations caused by the walling over with bricks of two windows were verified. The scenario providing the most stability in time and uniformity in space microclimate was checked by the simulations considering the compatibility with the safety range of the materials. Simulation outputs were then used to model for the scenarios physical quantities linked to moisture dynamics and salt crystallization (i.e. evaporation rates, height of rise, water stored, and water flow). The model determined a great variability of the thermo-hygrometric parameters among the tested ventilation solutions and allowed to establish how to improve the indoor microclimate in the building.
    Building and Environment 01/2014;
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    ABSTRACT: Chaotic systems without equilibrium points represent an almost unexplored field of research, since they can have neither homoclinic nor heteroclinic orbits and the Shilnikov method cannot be used to demonstrate the presence of chaos. In this paper a new fractional-order chaotic system with no equilibrium points is presented. The proposed system can be considered “elegant” in the sense given by Sprott, since the corresponding system equations contain very few terms and the system parameters have a minimum of digits. When the system order is as low as 2.94, the dynamic behavior is analyzed using the predictor–corrector algorithm and the presence of chaos in the absence of equilibria is validated by applying three different methods. Finally, an example of observer-based synchronization applied to the proposed chaotic fractional-order system is illustrated.
    Communications in Nonlinear Science and Numerical Simulation 01/2014; 19(9):2919–2927.
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    ABSTRACT: This work aims to develop an anaerobic digestion system, which allows recovering energy from olive wastes, solving the problem of their disposal. To reach this result, polyphenols, which are contained in olives inhibiting the digestion process, have to be abated. For this reason a new anaerobic digestion system able to treat the high concentration of polyphenols has been studied. Particularly, this system, composed by a storage of olive pomace, a mixing/washing unit, a pomace/water separation unit (decanter), an ultrafiltration unit and an anaerobic digester, has been numerically investigated to evaluate the anaerobic digestion key variables as a function of the hydraulic retention time (HRT), as well as the production of biogas for different values of the biomass yield factor. The results revealed that by abating polyphenols, the methane potential of the system under investigation rises from 7.5 molCH4/kgTSS to 11.7 molCH4/kgTSS, with an increment of about 56%, for HRT equal to 30 days.
    Energy Procedia 01/2014; 45:141–149.
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