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Development of 3D printable formulations containing CNT with enhanced electrical properties
No full textIn the loop simulator for the verification of small space platforms
No full textThe paper presents an end-to-end simulator aimed at supporting the engineering team in the design and verification activity across the whole product life cycle. The simulator is devoted to the analysis of small space systems, which present specific features if compared to large traditional platforms. Improving the understanding of the system early in the life cycle, and enhancing the verification process may help to increase the reliability and mission success of small-scale satellites while maintaining their key features of low cost and fast delivery. The simulator is designed through a Model and Simulation Based approach and allows performing "in-the-loop simulations" for the verification of functional and operational requirements at component, subsystem, and system level. The simulator is characterized by a modular architecture to adapt to several missions and different system configurations, also outside the space field. The core of the tool is a multi-processor workstation that sets up and runs the simulation, making use of a models database for the equipment and the mission environment, and a built-in interface unit to connect all the elements. The simulator has been successfully tested on a CubeSat project. Many test sessions were run and they are described into the detail in this article
Active flow control around simplified 3D bluff bodies
No full textIn the present work is illustrated a flow control technique designed with the aim of reducing the aerodynamic drag of a three-dimensional car model with a square-back rear part. The technique is based on continuous jets disposed in the periphery of the rear surface of the model. The design process of the entire investigation is illustrated. As a first step, a preliminary CFD study was performed to verify the effectiveness of the technique and its sensitivity to the flow control parameters. This CFD analysis assisted the design and the set up of the physical experiment. Several different measurements were performed and the entire chain of measurement is widely described evidencing the methodology. The assessment of this experimental methodology is also presented, which allowed to properly calibrate the different acquisition parameters and to reach adequate level of accuracy and repeatability of the measurements. Subsequently, the experimental investigation with the several diagnostic measurements allowed to understand and explain the flow characteristics. The wide range of flow control configurations evidenced, in fact, the effect that the forcing have on the pressure distribution, the flow structures and, consequently, on the drag value. The wake different sensitivity on the flow control parameters highlighted the most effective configuration which led to a drag reduction up to 12.6%. The analysis of pressure fluctuations, supported by the smoke visualization and the POD analysis evidenced the main flow structures present in the wake, their typical frequencies and their relation on the drag values. Finally the energy budget of the entire flow control system is presented in order to highlight the most efficient configurations and evidence the multi-criteria aspect of the active flow control technique presented
Assessment of vocal cord nodules: A case study in speech processing by using Hilbert-Huang Transform
No full text. Vocal cord nodules represent a pathological condition for which the growth of unnatural masses on vocal folds affects the patients. Among other effects, changes in the vocal cords' overall mass and stiffness alter their vibratory behaviour, thus changing the vocal emission generated by them. This causes dysphonia, i.e. abnormalities in the patients' voice, which can be analysed and inspected via audio signals. However, the evaluation of voice condition through speech processing is not a trivial task, as standard methods based on the Fourier Transform, fail to fit the nonstationary nature of vocal signals. In this study, four audio tracks, provided by a volunteer patient, whose vocal fold nodules have been surgically removed, were analysed using a relatively new technique: the Hilbert-Huang Transform (HHT) via Empirical Mode Decomposition (EMD); specifically, by using the CEEMDAN (Complete Ensemble EMD with Adaptive Noise) algorithm. This method has been applied here to speech signals, which were recorded before removal surgery and during convalescence, to investigate specific trends. Possibilities offered by the HHT are exposed, but also some limitations of decomposing the signals into so-called intrinsic mode functions (IMFs) are highlighted. The results of these preliminary studies are intended to be a basis for the development of new viable alternatives to the softwares currently used for the analysis and evaluation of pathological voice
Intrinsic map dynamics exploration for uncharted effective free-energy landscapes
No full textWe describe and implement a computer-assisted approach for accelerating the exploration of uncharted effective free-energy surfaces (FESs). More generally, the aim is the extraction of coarse-grained, macroscopic information from stochastic or atomistic simulations, such as molecular dynamics (MD). The approach functionally links the MD simulator with nonlinear manifold learning techniques. The added value comes from biasing the simulator toward unexplored phase-space regions by exploiting the smoothness of the gradually revealed intrinsic low-dimensional geometry of the FES
Impact response of adhesive reversible joints made of thermoplastic nanomodified adhesive
No full textThe impact response of a reversible adhesive joint is experimentally assessed in this work. Joint reversibility is improved with a system that uses nanomodification of the thermoplastic adhesive used for bonding plastic components. This system, coupled with electromagnetic induction, is able to guarantee separation of the joints without any damage to the substrates. Drop dart tests at different impact velocities are carried out on neat and nanomodified bonded joints in order to compare the impact behaviour before and after the introduction of nanoparticles. Experimental results show that the impact response, assessed in terms of peak load, absorbed energy and flexural stiffness, can be affected by the introduction of nanoparticles. This work shows that adhesive nanomodified joints represent an effective and applicable solution for the reversible assembling of semi-structural components subjected to low-velocity impact loads
An effective diversity promotion mechanism in grammatical evolution
No full textGrammatical Evolution is an Evolutionary Algorithm which can evolve programs in any language described by a context-free grammar. A sequence of bits (the genotype) is transformed into a string of the language (the phenotype) by means of a mapping function, and eventually into a fitness value. Unfortunately the flexibility brought by the mapping is also likely to introduce non-locality phenomena, reduce diversity, and consequently hamper the effectiveness of the algorithm. In this paper, we propose a novel technique for promoting diversity, able to operate on three different levels: genotype, phenotype, and fitness. The technique is quite general, independent both from the specific problem being tackled and from other components of the evolutionary algorithm, such as genotype-phenotype mapping, selection criteria, and genetic operators. We experimentally demonstrate its efficacy in a wide range of conditions and from different points of view. The results also confirm the preponderant importance of the phenotype-level analyses in diversity promotion
Engineering of Microbial Fuel Cells technology: Materials, Modelling and Architecture
No full textA Microbial fuel cell (MFC) is a bio-electrochemical reactor, able to convert chemical energy, contained in organic substrate, in electrical energy, thanks to the metabolic activity of microorganisms. Firstly, a fluid-dynamic modelling of different Microbial Fuel Cell configurations to study trajectories and concentration profile of the liquid containing the organic substrate during operation of the device was developed. The study of the device was joined with the study and the synthesis of carbon based aerogels to be used as new electrode materials, both for the anode and the cathode. The aim of the modelling was to understand what happen, from a fluid-dynamic point of view, inside the cell during operation. It was based on the application of equations from fluid-dynamics in order to study both the particle trajectories (using Navier-Stokes equations) and diffusion of substrate inside the reactor (using Fick's laws). Three different MFC architecture were investigated, starting from a circular shape. To increase the area of the reactor interested by flux exchange with respect to the one in the circular configuration, a new a squared MFC, with a non-alignment of the inlet and the outlet was proposed. Starting from results obtained during the simulation for the squared reactor, to accommodate the flux distribution, a further improvement in architecture was introduced: a drop-shape MFC, with a percentage of fluid area exchanged, higher than 96%. Another possibility to improve MFC performances, is the optimization of materials used as electrodes. To be an efficient electrode, a material must satisfy some important condition: biocompatibility, good electrically conductivity, resistance to electrolytic solutions and high surface area together with high porosity to allow the formation of the biofilm. Carbon based aerogels can satisfy all these properties. Organic aerogels were synthetized following a green approach, starting from marine polysaccharides, like agar and starch and then transformed in carbon based, thanks to a thermal process. The synthesis procedure is the sol-gel technique, followed by a drying process that can extract the liquid part of the gel, leaving the solid structure, without collapse the material. Synthetized materials were analyzed both structurally and morphologically in order to understand if porosity, surface area and chemical composition were appropriate. To enhance some of these properties, a post synthesis treatment was performed: the surface of the aerogel was treated with a KOH solution in order to enlarge pores and increase the porosity of the overall material. The optimized aerogel was tested, as anode, into the square shape MFC and compared with commercial carbon material having the same function. Due to their high surface area, high porosity and good interaction with microorganisms, aerogels presented better performances of commercial materials if used as anode in MFC. Considering, instead, the addition of amino acids as nitrogen source to the previous material, it allowed the used of polysaccharide aerogel, as cathode electrode able to catalyze the oxygen reduction reaction (ORR). They were tested in MFC, compared with the most used catalyst material in literature, that is platinum. Another alternative to platinum in the catalysis of the ORR, is represented by the metal oxide aerogels. In this work, aerogels based on MnxOy were tested. The synthesis of this material is similar to the previous one, with the difference of the addition of the manganese oxide directly between initial precursors. Through the thermal process, the organic part of the material is burned, leaving an oxide structure that is active from a catalytic point of view. After the morphological, structural and chemical analysis of the sample, the catalytic activity of the material was tested, as in the previous case, using the Rotating Ring Disk Electrode (RRDE) technique, in order to investigate its catalytic properties