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Supervised learning techniques are widely employed in credit card fraud detection, as they make use of the assumption that fraudulent patterns can be learned from an analysis of past transactions. The task becomes challenging, however, when it has to take account of changes in customer behavior and fraudsters’ ability to invent novel fraud patterns. In this context, unsupervised learning techniques can help the fraud detection systems to find anomalies. In this paper we present a hybrid technique that combines supervised and unsupervised techniques to improve the fraud detection accuracy. Unsupervised outlier scores, computed at different levels of granularity, are compared and tested on a real, annotated, credit card fraud detection dataset. Experimental results show that the combination is efficient and does indeed improve the accuracy of the detection., SCOPUS: ar.j, info:eu-repo/semantics/published

Methane/hydrogen combustion represents a concrete solution for the energy scenario to come. Indeed, the addition of hydrogen into the natural gas pipeline is one of the solutions foreseen to reduce CO2 emissions. Nevertheless, the replacement of methane by hydrogen will enhance the reactivity of the system, increasing NOx emissions. To overcome this issue, non-conventional combustion technologies, such as flameless combustion represent an attractive solution. This study aims to improve our understanding of the behaviour of methane/hydrogen blends under flameless conditions by means of experiments and simulations. Several experimental campaigns were conducted to test fuel flexibility for different methane/hydrogen blends, varying the injector geometries, equivalence ratio and dilution degree. It was found that a progressive addition of hydrogen in methane enhanced the combustion features, reducing the ignition delay time and loosing progressively the flameless behaviour of the furnace. Reducing the air injector diameter or increasing the fuel lance length were found to be efficient techniques to reduce the maximum temperature of the system and NOx emissions in the exhausts, reaching values below 30 ppm for pure hydrogen. MILD conditions were achieved up to 75%H2 in molar fraction, with no visible flame structures. Additionally, RANS-based simulations were also conducted to shed further light on the effect of adding hydrogen into the fuel blend. A sensitivity study was conducted for three different fuel blends: pure methane, an equimolar blend and pure hydrogen. The effect of chemistry detail, mixing models, radiation modeling and turbulence models on in-flame temperatures and NOx emissions was also studied. In particular, it was found that the usage of detailed chemistry for NOx, coupled with an adjustment of the PaSR model, filled the gap between experiments and predictions. Finally, a brute-force sensitivity revealed that NNH is the most important route for NOx production., SCOPUS: ar.j, info:eu-repo/semantics/published

Paper is a complex material consisting of a network of cellulose fibres at the micro-level. During manufacturing, the network is dried under restraint conditions due to tension in the paper web in machine direction. This gives rise to internal strains that are stored in the produced sheet. Upon exposure to a moisture cycle, these strains may be released. This results in permanent shrinkage that may cause instabilities such as curl or waviness of the sheet. The prime objective of this paper is to model this irreversible shrinkage and to link its magnitude to the properties of the fibres and of the network. For this purpose, randomly generated fibrous networks of different coverages (i.e. ratio of the area occupied by fibres and that of the sheet) are modeled by means of a periodic representative volume element (RVE). Within such RVEs, a finite element method combined with a kinematic hardening plasticity model at the scale of the fibres is used to capture the irreversible response. The computational results obtained demonstrate that the magnitude of the irreversible strains increases with coverage until a certain coverage and beyond that coverage decreases in magnitude. This phenomenon is explained by considering the area fraction of free-standing fibre segments relative to bonded fibre segments in the network. A structure–property dependency of irreversible strains at the sheet-level on the micro-structural parameters of the network is thereby established., SCOPUS: ar.j, info:eu-repo/semantics/published

In adsorption based separation techniques or in environmental applications where adsorption on a porous matrix is involved, the broadening of migrating bands of solutes varies with the characteristics of the adsorption isotherms and is generally overwhelming at solute concentrations deep in the non-linear region. We introduce here a novel concept to minimize concentration overloading dispersion: We show theoretically that a spatial alternation of Langmuir (L) and Anti-Langmuir (AL) zones along the displacement direction induces an accordion effect, i.e. an alternation of sharpening and dilution of the solute zones, reducing in the end the final broadening of the peak. We quantify in the parameter space of the problem the reduction in concentration overloading related band widening of the L-AL system compared to the pure L or AL cases. A numerical analysis of the solute transport reveals a dependence of solute spreading on the ratio of sample to stationary phase zone widths and on the intensity of the adsorption parameter. The initial position of the sample solvent in its surrounding liquid i.e. whether the displacement starts in a L or AL zone is also shown to have an influence on the dispersive behavior. An analysis is performed to highlight the optimal alternance geometry to minimize solute spreading., SCOPUS: ar.j, info:eu-repo/semantics/published

The Zinc level in many 6000 Al alloys (Al-Mg-Si-type) was set to a maximum of 0.03 wt% as common industrial practice. Concentrations above 0.03 wt% can modify the alkaline etching mechanism causing the surface to go from a desired smooth look associated with a grain boundary attack (GBA), into an undesired speckled appearance due to preferential grain etching (PGE), visible after anodizing. This significantly limits the ambition of reducing the carbon footprint of Aluminum by increasing the amount of recycled material in the production process. Because Cu has been reported to counteract this negative effect of Zn, the present study is dedicated to contribute to the understanding of this interaction and is focused on Zn and Cu in peak aged AlMgSi alloys. The chemical composition of the various precipitates formed in two Al6063 alloys was studied by means of TEM and EDX, whereby Zn was found in the Q phase (AlMgSiCu) grain boundary precipitates. Two alloys, with different content of Cu and Zn were studied. The Zn/Cu ratio in the bulk was similar for both alloys, but the level of Zn in the Cu containing Q particles in the grain boundaries was different. The increased Zn concentration in Q phase precipitates is believed to decrease the potential of the precipitates with respect to the surrounding matrix. Thus, the Cu/Zn ratio in these alloys is extremely important as it defines the potential differences that in turn cause either GBA or PGE., SCOPUS: ar.j, info:eu-repo/semantics/published

The growing share of intermittent renewable energy sources in electricity production allows for a significant reduction of the emissions of CO 2 and other pollutants from conventional, thermal power plants. As a side effect, it also leads to a noticeable increase of the number of start-ups and fast load transients encountered by those power plants used as back-up units. During such transient phases, the performances of those units in terms of pollutant emissions and thermal efficiency are however degraded, which results in a possible reduction of the environmental benefits of renewables that was not yet quantified. In this study, ten years of process data from a representative, large scale gas-fired combined cycle plant that underwent such a transition are analysed to assess the impact of frequent start-ups and load cycling on its average specific CO 2 and NO x emissions (per produced MWh e ). While start-up and fast transient phases historically contributed to less than 5% of the produced power, this share now reaches 5−20%. As a consequence of the increased occurrence of such transients, the average specific NO x emissions increase by 30 to 80%, from 140 up to 250 g/MWh e ,and the average specific CO 2 emissions, less impacted, increase by 2 to 4%, from 335 kg/MWh e up to 350 kg/MWh e .The impact of these findings on the expected reduction of CO 2 and NO x emissions attributable to the deployment of renewables is assessed. NO x emissions reduction is significantly lower than expected, due to the increased transient operation of conventional units. For shares of renewable sources lower than 30%, the additional NO x emissions caused by peak demand operation of the thermal units compensate the emissions saved by decreasing their number of operating hours, resulting in a status quo in terms of global NO x emissions for the most optimistic scenario in terms of LCA emissions from renewable sources. For other scenarios, the global NO x emissions even increase for shares of renewables lower than 30%, up to 110% of the initial value (no renewables). As CO 2 emissions are much less sensitive to transient phases, the expected CO 2 emissions reduction is marginally affected by peak demand operation. Means of reducing both the occurrence of transient phases (at the level of the grid), and the related NO x emission peaks (at the level of the power plants) should be investigated, for a better integration of renewable sources and existing thermal assets., SCOPUS: ar.j, info:eu-repo/semantics/published

The present work investigates the reference signal reconstruction method for passive coherent location (PCL) radars exploiting Digital Video Broadcasting-Terrestrial (DVB-T) signals. The reference signal reconstruction improves the signal-to-noise ratio (SNR) of the reference signal, which enhances the detection probability for DVB-T based PCL systems. The existing approach for the reference signal reconstruction is performed by demodulating the received reference signal to retrieve the transmitted quadrature amplitude modulation (QAM) symbols and modulate them to obtain the reconstructed signal. For low SNR values, the QAM symbol detection is accompanied with a significant error, which leads to a mismatch between the reconstrued signal and the exact one. Consequently, the expected improvement due to the signal reconstruction is limited. In this work, we propose an optimum reconstruction method which filters the detected QAM symbol prior to the remodulation step. To validate the proposed method, we retrieved analytic expressions for the detection and false-alarm probabilities and verified them through Monte-Carlo simulations. In addition, real-data sets were used to evaluate the proposed method performances. The results show that the proposed method outperforms the conventional one by extending the feasibility of the reference signal reconstruction for low SNR values., SCOPUS: ar.j, info:eu-repo/semantics/published

Duplex stainless steels (DSSs) are corrosion-resistant alloys extensively used in aggressive environments. Cast DSSs may be selected for pipes, valves and pumps in chemical, petrochemical and nuclear industries. The grade steel ASTM A890 1B is an example of cast DSS with 2.7-3.3%Cu addition. Copper increases the resistance to many types of corrosion, especially in non-oxidizing environments. When the copper content is higher than 2%, the steel can be precipitation-hardened. In this work, the precipitation hardening of a DSS ASTM A890 1B steel with 3.0%Cu was studied and modeled for aging temperatures in the 450-600 °C range. Copper precipitates in the ferrite phase, but remains in solid solution in the austenite. The age hardening curves were modeled by ΔH = K(t) n model, where ΔH is the increase in hardness, t is the aging time, and K and n are constants to be determined. The microstructure and substructure were investigated by scanning electron and transmission electron microscopes., SCOPUS: ar.j, info:eu-repo/semantics/published

Self-assembling robots have the potential to undergo autonomous morphological adaptation. However, due to the simplicity in their hardware makeup and their limited perspective of the environment, self-assembling robots are often not able to reach their potential and adapt their morphologies to tasks or environments without external cues or prior information. In this paper, we present supervised morphogenesis — a control methodology that makes self-assembling robots truly flexible by enabling aerial robots to exploit their elevated position and better view of the environment to initiate and control (hence supervise) morphology formation on the ground. We present results of two case studies in which we assess the feasibility of the presented methodology using real robotic hardware. In the case studies, we implemented supervised morphogenesis using two different aerial platforms and up to six self-assembling autonomous robots. We furthermore quantify the benefits attainable for self-assembling robots through cooperation with aerial robots using simulation-based studies. The research presented in this paper is a significant step towards realizing the true potential of self-assembling robots by enabling autonomous morphological adaptation to a priori unknown tasks and environments., SCOPUS: ar.j, info:eu-repo/semantics/published

In the presence of temperature gradients along the gas-liquid interface, a liquid bridge is prone to hydrothermal instabilities. In the case of a coaxial gas stream, in addition to buoyancy and thermocapillary forces, the shear stresses and interfacial heat transfer affect the development of these instabilities. By combining experimental data with three-dimensional numerical simulations, we examine the evolution of hydrothermal waves in a liquid bridge with with a gas flow parallel to the interface. The gas moves from the cold to the hot side with a constant velocity of and its temperature is the main control parameter of the study. When the thermal stress exceeds a critical value, a three-dimensional oscillatory flow occurs in the system. A stability window of steady flow has been found to exist in the map of dynamical states in terms of gas temperature and applied thermal stress. The study is carried out by tracking the evolution of hydrothermal waves with increasing gas temperature along three distinct paths with constant values of: Path 1 is selected to be just above the threshold of instability while path 2 traverses the stability window and path 3 lies above it. We observe a variety of dynamics including standing and travelling waves, determine their dominant and secondary azimuthal wavenumbers, and suggest the mathematical equations describing hydrothermal waves. Multimodal standing waves, coexistence of travelling waves with several wavenumbers rotating in the same or opposite directions are among the most intriguing observations., SCOPUS: ar.j, info:eu-repo/semantics/published

Dip coating is a common technique used to cover a solid surface with a thin liquid film, the thickness of which was successfully predicted by the theory developed in the 1940s by Landau & Levich (Acta Physicochem. URSS, vol. 17, 1942, pp. 141-153) and Derjaguin (Acta Physicochem. URSS, vol. 20, 1943, pp. 349-352). In this work, we present an extension of their theory to the case where the dipping bath contains two immiscible liquids, one lighter than the other, resulting in the entrainment of two thin films on the substrate. We report how the thicknesses of the coated films depend on the capillary number, on the ratios of the properties of the two liquids and on the relative thickness of the upper fluid layer in the bath. We also show that the liquid/liquid and liquid/gas interfaces evolve independently from each other as if only one liquid were coated, except for a very small region where their separation falls quickly to its asymptotic value and the shear stresses at the two interfaces peak. Interestingly, we find that the final coated thicknesses are determined by the values of these maximum shear stresses., SCOPUS: ar.j, info:eu-repo/semantics/published

Thermodiffusion, which leads to a component separation in a mixture due to the thermal gradient, still does not have an unambiguous microscopic picture. Therefore, experimental studies, especially in convection free environment, are important. As part of the 4th campaign on the DCMIX project, thermodiffusion experiments on three compositions of the toluene-methanol-cyclohexane ternary mixture, on a mixture of fullerene-tetralin-toluene and on a mixture of polystyrene-toluene-cyclohexane have been performed in microgravity conditions on board the International Space Station. A binary mixture of polystyrene-toluene has been filled into the companion cell for the campaign. The Selectable Optical Diagnostics Instrument (SODI), wich is a two-wavelength Mach-Zehnder interferometer for the ternary mixtures, plus a monochromatic Mach-Zehnder interferometer for the binary mixture, has been used in order to obtain the temperature and the concentration fields in the cells. Precisely, it is a 5-steps phase-shifting interferometry technique which is implemented with SODI, producing by means of laser illumination a set of 5 phase-shifted images of π/2 between them as function of the time. A total of 58 runs of various durations and at different mean temperatures have been conducted. Here, we evaluate the contrast of the interferograms, the quality in the phase stepping, the stability of the thermal regulation of the experiments and the level of environmental disturbances on board the space station during the campaign., SCOPUS: ar.j, info:eu-repo/semantics/published

Industrial denitrification catalyst monoliths are regularly tested in controlled lab-scale conditions to quantify their activity. As mass transfer phenomena occurring inside the channels of the monoliths have an important impact on the global denitrification kinetics, activity measurements must be conducted in well-known conditions in terms of sample geometry and gaseous flow regimes, among others. The lack of accurate mass transfer correlations for the complex flows at stake however prevents any accurate generalisation of the test results. In this paper, we propose a semi-empirical method for the quantification of contribution of mass transfer to the global denitrification kinetics for any given test bench. It is based on the experimental adjustment of mass transfer correlations presenting a suitable form. Mass transfer can therefore be decoupled from the intrinsic kinetics and large ranges of conditions can be covered by conducting a limited number of measurements., SCOPUS: ar.j, info:eu-repo/semantics/published

Hydrogen chloride is found in important hydrogen gas streams of the chemical industry and needs to be removed for safety and environmental concerns. Here, a systematic study is presented on HCl removal from hydrogen gas by adsorption on zeolites, including cation free and high cation loaded materials, as well as ion-exchanged zeolites (with alkali, alkaline earth and transition metal ions). The HCl removal performance was studied by a fixed-bed breakthrough method under high gas velocities (>0.3 m/s), at high pressures (30 bar) and at room temperature, and with low HCl concentrations (, SCOPUS: ar.j, info:eu-repo/semantics/published

When a liquid drop is placed on a highly superheated surface, it can be levitated by its own vapour. This remarkable phenomenon is referred to as the Leidenfrost effect. The thermally insulating vapour film results in a severe reduction of the heat transfer rate compared to experiments at lower surface temperatures, where the drop is in direct contact with the solid surface. A commonly made assumption is that this solid surface is isothermal, which is at least questionable for materials of low thermal conductivity, resulting in an overestimation of the surface temperature and heat transfer for such systems. Here we aim to obtain more quantitative insight into how surface cooling affects the Leidenfrost effect. We develop a technique based on Mach-Zehnder interferometry to investigate the surface cooling of a quartz plate by a Leidenfrost drop. The three-dimensional plate temperature field is reconstructed from interferometric data by an Abel inversion method using a basis function expansion of the underlying temperature field. By this method we are able to quantitatively measure the local cooling inside the plate, which can be as strong as 80 K. We develop a numerical model which shows good agreement with experiments and enables extending the analysis beyond the experimental parameter space. Based on the numerical and experimental results we quantify the effect of surface cooling on the Leidenfrost phenomenon. By focusing on the role of the solid surface we provide new insights into the Leidenfrost effect and demonstrate how to adjust current models to account for non-isothermal solids and use previously obtained isothermal scaling laws for the neck thickness and evaporation rate., SCOPUS: ar.j, info:eu-repo/semantics/published

We explore the implications of an increase in clean technology spillovers between developed and developing countries. We build a game of abatements in which players are linked with technology spillovers determined by an initial choice of absorptive capacities by developing countries. We show that, within a non-cooperative framework, the response of clean technology investments in developed countries to an increase in cross-country technology spillovers is ambiguous. If the marginal benefits of these additional abatements are not sufficiently high, developed countries have a strategic incentive to decrease investments. Such a strategic response jeopardizes the initial effects of an increase in technology spillovers on climate change mitigation and decreases the incentives for developing countries to enhance their absorptive capacities., SCOPUS: ar.j, info:eu-repo/semantics/published

We analyze 78 case studies that applied an input-output (IO) model for waste management analyses. We categorize all IO models into four types (waste extended IO (WEIO), waste IO (WIO), physical IO (PIO) and hybrid IO (HIO)). We then define each model within a waste analysis framework, and carry out a bibliometric analysis. Our comparative analysis is twofold. Firstly, to compare the models conceptually, we analyze and discuss three characteristics of the models – the units of intersectoral flows, the modelling of waste and the relation with mass balance principle. Secondly, we analyze and discuss six criteria pertaining to the functionalities of the models, – the waste generation accounting, the purpose of the modelling, the geographical scale, the temporal dimension, the coupling of the IO models with other methods and the level of details of waste treatment sectors and waste types. Our findings are fourfold. First, there is increasing interest in assessing waste management policies with IO models; WIO models are the most applied ones, followed by WEIO models; PIO models are the least widely applied. Second, WIO models have the most mature analytical framework, and HIO models are conceptually the most powerful. Third, there is no cause-effect link between the conceptual characteristics and the functionalities of IO models. The IO models have been widely used for diverse applications in waste management at economy-wide level, but there is potential for several other applications. Fourth, the main limitation of all models is data related: future efforts should include more effective monitoring and collection of physical IO data and waste data, as well as the development of methods for consistent data mining., SCOPUS: re.j, info:eu-repo/semantics/published

A γ–irradiated bovine albumin serum-based nanoparticle was characterised structurally, and functionally. The nanoparticle was characterised by A.F.M. D.L.S, zeta potential, T.E.M. gel-electrophoresis, and spectroscopy. We studied the stability of the nanoparticle at different pH values and against time, by fluorescence spectroscopy following the changes in the tryptophan environment in the nanoparticle. The nanoparticle was also functionalized with Folic Acid, its function as a nanovehicle was evaluated through its interaction with the hydrophobic drug Emodin. The binding and kinetic properties of the obtained complex were evaluated by biophysical methods as well as its toxicity in tumor cells. According to its biophysics, the nanoparticle is a spherical nanosized vehicle with a hydrodynamic diameter of 70 nm. Data obtained describe the nanoparticle as nontoxic for cancer cell lines. When combined with Emodin, the nanoparticle proved to be more active on MCF-7 cancer cell lines than the nanoparticle without Emodin. Significantly, the albumin aggregate preserves the main activity-function of albumin and improved characteristics as an excellent carrier of molecules. More than carrier properties, the nanoparticle alone induced an immune response in macrophages which may be advantageous in vaccine and cancer therapy formulation., SCOPUS: ar.j, info:eu-repo/semantics/published

Modern cities are growing ecosystems that face new challenges due to the increasing population demands. One of the many problems they face nowadays is waste management, which has become a pressing issue requiring new solutions. Swarm robotics systems have been attracting an increasing amount of attention in the past years and they are expected to become one of the main driving factors for innovation in the field of robotics. The research presented in this paper explores the feasibility of a swarm robotics system in an urban environment. By using bio-inspired foraging methods such as multi-place foraging and stigmergy-based navigation, a swarm of robots is able to improve the efficiency and autonomy of the urban waste management system in a realistic scenario. To achieve this, a diverse set of simulation experiments was conducted using real-world GIS data and implementing different garbage collection scenarios driven by robot swarms. Results presented in this research show that the proposed system outperforms current approaches. Moreover, results not only show the efficiency of our solution, but also give insights about how to design and customize these systems., SCOPUS: cp.p, info:eu-repo/semantics/published

The measurement of fluid velocity in the vicinity of wavy interfaces by means of Particle Image Velocimetry (PIV) still constitutes a challenge. Besides the experimental complexities such as appropriate seeding, reflections due to gradients in refractive indices, aberrations, etc. also the image processing phase constitutes a critical component. Ignoring bias errors introduced by laser reflections near the interface, strong velocity gradients are typically encountered near the curved liquid/gas interface and are detrimental to the common cross-correlation analysis. These effects are exacerbated by the use of traditional rectangular static cross-correlation windows. Moreover, dynamic boundaries suffer from a certain loss in reliability due to the difference in number of particles located in a specific physical region between the two frames. In this paper we present an improved algorithm enhancing the accuracy of the velocity vector detection in dynamic wavy flows. This algorithm divides the fluid domain in subregions (i.e. bulk, intermediate, vicinity and interface) and applies to each region different features (such as image patching, window relocation and forward difference finite schemes) and ad hoc predictors. Its assessment is performed on the basis of synthetic images, which reproduce a wavy motion similar to the one encountered when fluid in a cylindrical reservoir undergoes sloshing. When juxtaposed with a standard PIV code, numerical errors are shown to strongly diminish while improving the spatial resolution approaching the interface. The algorithm is finally applied to experimental PIV images of water sloshing in a cylindrical reservoir to provide more reliable results at the interface, contrary to standard PIV codes., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A low Young's modulus is required for titanium alloys used in orthopedic implants, such as hip prosthetic stems, in order to avoid stress shielding due to a large difference in Young's modulus between the prosthetic stem and the cortical bone. The low Young's modulus has been observed to occur in metastable β-Ti alloys by precipitation of a stress-induced α″ martensite during cold deformation. Under this context, the Influence of thermo-mechanical processing on the microstructure and mechanical properties of the metastable β Ti–29Nb–2Mo–6Zr alloy was studied as well as the influence of the degree of deformation by cold rolling with subsequent annealing after homogenization heat treatment. The alloy presents a β microstructure after solution heat treatment at 1000 °C for 24h, followed by water quenching, while posterior cold rolling induces the precipitation of α” martensite. Young's modulus decreases and hardness increases with the degree of deformation. The annealed samples showed higher hardness and Young's modulus than the cold rolled samples. A thickness reduction of 90% maximizes the hardness/Young's modulus ratio and optimizes the required mechanical properties for orthopedic implants. The results indicate that the alloy is a promising alternative for the widely used Ti–6Al–4V., SCOPUS: ar.j, info:eu-repo/semantics/published

Loss of Offsite Power (LOOP) is the most dominant initiating event in the Core Damage Frequency (CDF) of Nuclear Power Plants (NPPs). Since the frequency of occurrence of LOOP depends on the grid configuration, outage schedule, load flow, etc. even a relevant generic frequency may result in significant uncertainty. In this study, an analytical hybrid methodology, which combines the probabilistic and deterministic modules, is introduced to systematically estimate the frequency of Grid-related LOOP. The proposed probabilistic module develops the relevant event-trees and fault-trees in SAPHIRE7 to identify the LOOP sequences upon the response of the distance protection system to a fault on the transmission lines. Meanwhile, the identified scenarios are confirmed based on the simulation results from the deterministic module in DIgSILENT-PowerFactory15.1. 15-out-of-48 scenarios (100-out-of-300 sequences) are identified as grid-related LOOP upon faults on the four transmission lines of the test grid, and result in 1.76E-06/yr for the grid-related LOOP frequency. The developed methodology enables us to trace a LOOP chain, from a primitive presumed fault through the progress of the cascade. The grid-related LOOP scenarios in a certain network can be ranked probabilistically, with the desired level of details in both deterministic and probabilistic modules., SCOPUS: ar.j, info:eu-repo/semantics/published

A new concept of vapour condenser is proposed to solve the drainage problem and to provide an effective condensate flow under weightlessness conditions. The concept combines the capability of a curvilinear surface to drive liquid, and a combination of a porous media and a pump, as an active condensate retraction system. The porous media collects and stores the condensed fluid and acts as a barrier for the vapour phase. Hydrodynamic validation of the liquid flow was done against retraction overflow under terrestrial conditions. It was figured out that the time available for adjusting the retraction system to avoid film disturbances decreased non-linearly with an increase in retraction overflow. The behaviour of the proposed condenser with the retraction system was tested under weightlessness condition during the ESA parabolic flights campaign as a part of concept validation. Three porous media with different values of the pore size and material were tested. It was found that the combination of the pump and porous media helped to improve the condensate flow. It was observed that the stabilisation effect was influencing the condensate flow not only during weightlessness condition but also under acceleration disturbances during the campaign., SCOPUS: ar.j, info:eu-repo/semantics/published

We present a combined analytical approach and numerical study on the stability of a ring bound to an annular elastic substrate, which contains a circular cavity. The system is loaded by depressurizing the inner cavity. The ring is modeled as an Euler-Bernoulli beam and its equilibrium equations are derived from the mechanical energy which takes into account both stretching and bending contributions. The curvature of the substrate is considered explicitly to model the work done by its reaction force on the ring. We distinguish two different instabilities: periodic wrinkling of the ring or global buckling of the structure. Our model provides an expression for the critical pressure, as well as a phase diagram that rationalizes the transition between instability modes. Towards assessing the role of curvature, we compare our results for the critical stress and the wrinkling wavelength to their planar counterparts. We show that the critical stress is insensitive to the curvature of the substrate, while the wavelength is only affected due to the permissible discrete values of the azimuthal wavenumber imposed by the geometry of the problem. Throughout, we contrast our analytical predictions against finite element simulations., SCOPUS: ar.j, info:eu-repo/semantics/published

Injectable hydrogels have gained lots of attention as cell and growth factor carrier in tissue engineering. Here, we developed a novel graphene oxide (GO) reinforced poly(N-isoproplylacrylamide)/chitosan temperature-responsive (pNCG) hydrogel, and the gelation temperature was around 36.4 °C. Then, vascular endothelial cells (VECs) laden pNCG hydrogel was fabricated by encapsulating VECs through the sol–gel transfer process. Also, a sequential release system of monocyte chemoattractant protein-1 (MCP-1) and vascular endothelial growth factor (VEGF) was delicately designed and incorporated into VECs-laden pNCG hydrogel. In vitro and in vivo experiments confirmed that the VECs could proliferate into hydrogel, as well as feasible in-growing angiogenesis. Thus, the injectable pNCG hydrogel holds great potential for biomedical applications., SCOPUS: ar.j, info:eu-repo/semantics/published

Brush seals have been extensively studied for the last thirty years as an advanced sealing solution for gas turbine engines. The research is always aimed towards the reduction of the leakage flow, that has direct repercussions on the specific fuel consumption, the thrust-to-weight ratio, and the emission of pollutants. In addition, the sealing device must cope with side effects related to higher interface speeds, rotordynamics issues, or durability. Brush seals main assets are their excellent leakage performance with low friction properties compared to other contact seals like lip seals, and their ability to withstand rotor radial excursion without permanent damage. However, proper design optimization cannot be performed without the inclusion of the tribological performance. This paper presents a parametric investigation of the friction properties of carbon fibre brush seals as a function of the fibre pack geometry and the rotational speed. Carbon fibre and commonly used metallic brush seals present fundamentally different behaviour in presence of differential pressure or rotational speed. This paper also proposes an alternative method to predict the brush seal torque, based on measurements with a torque sensor. Heat generation was also evaluated with a thermographic camera. Both methods ensured consistency between results., SCOPUS: ar.j, info:eu-repo/semantics/published

Beam-column joints are critical component in the load path of reinforced concrete (RC) frames, due to their role in transferring loads among different RC frame components. The loss of a ground corner column in a RC frame turns an exterior joint into an inverted knee joint and recent code provisions for exterior joints are not sufficient to knee joints because of reinforcement defects in terms of joint vertical stirrups and improper column bar anchorage. This paper investigates numerically the behaviour of these joints under a closing moment using nonlinear finite element (FE) analysis with LS-DYNA. Beam’s bar anchorage type and joint vertical stirrups are the main parameters considered next to concrete compressive strength, longitudinal reinforcement ratio and lateral beam effect. This study indicates that, anchorage beam’s bar with U shaped produces better behaviour than 90° standard hooks or headed ends. Contribution of joint vertical stirrups is more influential with headed bars anchorage. Increasing concrete compressive strength and beam reinforcement ratio improve joint ultimate capacity. The presence of lateral beams reduces the rate of concrete degradation in the joint after reaching ultimate capacity and increases joint carrying capacity., SCOPUS: ar.j, info:eu-repo/semantics/published

This paper presents an automated approach to build computationally Representative Volume Elements (RVE) of open-foam cellular materials, enabling the study of the effects of the microstructural features on their macroscopic behavior. The approach strongly relies on the use of distance and level set functions. The methodology is based on the extraction of random tessellations from inclusion packings following predetermined statistical packing distribution criteria. With the help of simple recombination operations on the distance fields, the tessellations are made to degenerate in Laguerre tessellations. Predetermined morphological characteristics like strut cross-section variation based on commercially available materials are applied on the RVE to ensure the extraction of closely matching models using simple surface extraction tools, and a detailed morphology quantification of the resulting RVEs is provided by comparing them with experimental observations. The extracted RVE surface is then treated with smoothening criteria before obtaining a 3D tetrahedralized model. This model can then be exported for multi-scale simulations to assess the effects of microstructural features by an upscaling methodology. The approach is illustrated by the simulation of a compression test on an RVE incorporating plasticity with geometrically non-linear behavior., SCOPUS: ar.j, info:eu-repo/semantics/published

Metastable β-type Ti alloys with non-toxic addition elements such as Mo, Zr, Sn, Ta and Nb were developed as an alternative to the widely used Ti-6Al-4V alloy for biomedical applications. These alloys possess enhanced biocompatibility and reduced elastic modulus in comparison with Ti-6Al4V. Moreover, for orthopedic implants, low Young's modulus is required in order to avoid the stress shielding phenomenon. This study analyzes the microstructure and mechanical properties of a new Ti-12Mo-8Nb alloy after hot swaging, annealing at 950 ºC for 1h and water quenching. The alloy was characterized by X-ray diffraction, optical microscopy and transmission electron microscopy. Tensile tests were performed at room temperature. Young's modulus and hardness values were also measured. The structural characterization reveals a metastable β structure containing only a small amount of α and ω phases. Exhibiting a lower Young's modulus than Ti-6Al-4V and other previously studied Ti-Mo-Nb alloys, the Ti-12Mo-8Nb alloy can be a promising alternative for orthopedic application., SCOPUS: cp.j, info:eu-repo/semantics/published

Cd1-xZnxS thin films have been studied extensively as window layers for solar cell applications. However, a mismatch between the Cd1-xZnxS and copper-indium-gallium-selenide absorber layers increases with Zn film concentration, which reduces the device eficiency. In this work, Cd1-xZnxS thin films with low Zn concentrations were analyzed. The effect of the addition of different molar Zn concentrations to the reaction mixture on the growth mechanism of Cd1-xZnxS thin films and the influence of these mechanisms on structural, optical and morphological properties of the films has been studied. Cd1-xZnxS thin films were synthesized by chemical bath deposition using an ammonia-free alkaline solution. Microstructural analysis by X-ray diffraction showed that all deposited films grew with hexagonal structure and crystallite sizes decreased as the Zn concentration in the film increased. Optical measurements indicated a high optical transmission between 75% and 90% for wavelengths above the absorption edge. Band gap value increased from 2.48 eV to 2.62 eV, and the refractive index values for Cd1-xZnxS thin films decreased as the Zn increased. These changes in films and properties are related to a modification in growth mechanism of the Cd1-xZnxS thin films, with the influence of Zn(OH)2 formation being more important as Zn in solution increases., SCOPUS: ar.j, info:eu-repo/semantics/published

We consider the control of distributed systems composed of subsystems communicating asynchronously; the aim is to build local controllers that restrict the behavior of a distributed system in order to satisfy a global state avoidance property. We model our distributed systems as communicating finite state machines with reliable unbounded FIFO queues between subsystems. Local controllers can only observe their proper local subsystems and do not observe the queues. To refine their control policy, they can use the FIFO queues to communicate by piggybacking extra information to the messages sent by the subsystems. We define synthesis algorithms allowing to compute the local controllers. We explain how we can ensure the termination of this control algorithm by using abstract interpretation techniques, to overapproximate queue contents by regular languages. An implementation of our algorithms provides an empirical evaluation of our method. © 2011 IEEE., SCOPUS: cp.p, info:eu-repo/semantics/published

The dilution is an event that have a high influence on the microstructure and, consequently, in the properties of weld claddings. The present study evaluated the effect of dilution level on the microstructure of the fusion zone of alloy Inconel 686 weld claddings. The claddings were welded by the TIG cold wire feed process. The dilution was calculated from the geometric characteristics and based on chemical composition of the materials obtained by energy dispersive X-ray spectroscopy and optical emission spectroscopy. The microstructure of all claddings were composed by a γ-FCC matrix with some minor precipitates. These particles are called in literature as topologically closed-packed phases (TCP). These precipitates assumed several morphological aspects, being the shapeless morphology observed in more frequency in all claddings evaluated, independent of dilution level. A phase with lamellar morphology, which growth establishing an orientation relationship with the γ-FCC matrix solidification direction, was observed only in claddings with a low dilution level. In addition, a shapeless phase with a fine precipitation aggregated was observed in claddings with a high dilution level., SCOPUS: ar.j, info:eu-repo/semantics/published

In a channel flow with a sudden expansion, whether for three-dimensional (3-D) pipe and channel flows, or for two-dimensional (2-D) channel flow, it is known that increasing the Reynolds number beyond a critical value induces a symmetry breaking Pitchfork bifurcation. The linear stability analysis of the symmetric steady solution enables the to be determined efficiently and thus the influence of the expansion ratio ,defined as the ratio between upstream and downstream diameter regarding the expansion, to be explored. In this study, we investigate the behaviour of the flow after 2-D sudden expansions while varying the and the inlet flow profile, e.g. corresponding to a transition profile between a plug and a Poiseuille flow that could be reached for a flow after a sudden constriction upstream. Results demonstrate that imposing a plug flow at the inlet gives a higher than any other profile and that the concomitant recirculation zones are shorter. We show that these results can be rationalized using basic convection-diffusion arguments., SCOPUS: ar.j, info:eu-repo/semantics/published

The hydropower sector has recently raised the interest in pump as turbine (PaT) that can be a valid trade-off between capital cost and performance in micro-scale installations. Nevertheless, the modest efficiency of PaTs often restricts their exploitation. In this paper, available experimental data are used to tune a numerical model which aims to investigate the effect of the pump cutwater design on the PaT performance to improve the hydraulic efficiency. Because of its finite thickness, the cutwater interferes with the flow at the runner inlet, and generates local flaws in the velocity field such as swirl and deviations of the streamlines which limit the machine performance. To identify the geometrical characteristics of the cutwater impacting on the PaT performances, different values of stretching and thickness of the cutwater are studied at variable inclination by computational fluid dynamics (CFD) simulations. A multivariate regression method is applied on the CFD results to build a surrogate model of the PaT hydraulic characteristics as a function of the geometrical parameters of the machine cutwater. Based on this model, an optimization problem is solved to identify the most advantageous geometrical asset of the PaT cutwater to maximize the efficiency. The results highlight that the length and the cutwater angle are the most affecting variables in favouring a tangential component at the entrance of the runner. The hydraulic efficiency peak of the optimized geometry results to be 86.3%, while the baseline configuration records an efficiency of 82.4%, and the Ψ−ϕ characteristic moves the best efficiency point towards higher head (+7.5%) and lower discharge (−13.0%). The proposed methodology allows identifying the best geometrical characteristics of the PaT cutwater to maximize the performances while significantly reducing the computational time., SCOPUS: ar.j, info:eu-repo/semantics/published

Simulations of atmospheric entry of spacecraft and satellites require accurate knowledge of thermo-physical properties such as heat capacity in a wide temperature range. However, the characterization of this quantity is not straightforward for carbon composites at high temperatures, due to pyrolysis reactions that occur in the material. We develop a methodology for determining the heat capacity and required heat of pyrolysis for carbon composites in these conditions. The methodology consists of three steps: organic elemental analysis to determine composition, differential scanning calorimetry experiments on the different components to determine apparent heat capacity, and computations to separate the apparent heat capacity into heat capacity and heat of pyrolysis. This methodology is applied to the ZURAM® carbon/phenolic ablator from room temperature up to 1100 K. The results obtained were compared to separate analyzes of the different components of the material, assuming that heat capacity is an additive property. It was found that compressing the samples into disks provides improved resolution and repeatability for low density materials. This provided a determination of the heat capacity of the decomposing composite with a relative standard deviation, SCOPUS: ar.j, info:eu-repo/semantics/published