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Electrochemical performance of solid oxide fuel cell: Experimental study and calibrated model
No full textCampi di cemento. Verso un'economia circolare: agricoltura locale per la tutela e la valorizzazione del territorio
No full textThe climate change effects on the environment are particularly perceived in the urban habitat due to excessive soil cementation; moreover, there are negative consequences that affect those lands allocated to agriculture. Despite the crisis of the Italian construction industry, cities and suburbs continue to steal useful land for agricultural purpose, destroying a valuable resource. Fertile soil is, in fact, an exhaustible common good, a fundamental asset to achieve a more sustainable balance between the city and the country. Investing in the recovery of rural areas would induce a virtuous process of circular economy, based on local agricultural production, small-scale community relationship, valorization and reclamation of the territory, and the enhancement of rural property heritage. Such economy would be a possible solution for a more resilient, durable and sustainable territory
Quench propagation in a TF coil of the EU DEMO
No full textThe design of a suitable quench protection system is fundamental for the safe operation of superconducting magnets and in turn requires the accurate simulation of the quench transient. The quench propagation in a toroidal field (TF) coil for the future European fusion reactor (EU DEMO) is analyzed here considering the latest, layer-wound winding pack (WP) design proposed by ENEA. The thermal-hydraulic model of a TF coil implemented in the 4C code is updated by including the external cryogenic circuits of the WP and of the casing cooling channels and proposing a preliminary layout of the quench lines. Three different locations are considered for the quench initiation: maximum temperature margin in the WP, and minimum and maximum temperature margin on the same turn of the innermost layer. The evolution of the main electrical and thermal-hydraulic parameters is simulated, such as voltage along each layer, quench front propagation both along and across the layers, hot spot temperature, pressurization of the coil and coolant mass flow rate at the coil boundaries, so that the 4C code provides a reliable (in view of its validation) and detailed virtual monitor of what happens inside the coil during the quench transient. In all cases considered, the ENEA design is predicted to satisfy the present (i.e., ITER) design criteria concerning the maximum allowed hot spot temperature
BEM coupling with the FEM fictitious domain approach for the solution of the exterior Poisson problem and of wave scattering by rotating rigid bodies
No full textThermally conductive polymer/graphene-related materials nanocomposites prepared by melt reactive processing
No full textPolymer nanocomposites containing graphene-related materials attracted a wide research interest thanks to the combination of the processability, lightweight and corrosion resistance typical of polymers, with the outstanding properties of graphene-related materials, including mechanical properties, thermal conductivity and electrical conductivity. Nanocomposites exploiting graphene-related materials are indeed showing interesting properties and several industrial applications for such nanomaterials are currently being developed, including structural materials, as well as functional materials, electrodes and conductors in flexible electronics, waste heat management, gas-barrier materials, etc., also taking into advantage of the large European initiative for graphene research, development and application called Graphene Flagship (http://graphene-flagship.eu/). This thesis aims to the preparation of polymer nanocomposites, exploiting graphene-related materials, by the development of industrially viable preparation methods, for the application as heat management materials. These are currently of interest in several application fields, including low temperature heat recovery, heat exchange in highly corrosive environments as well as heat dissipation in electronics and flexible electronics. Beside the thermal conductivity property, this PhD thesis was aimed at the fundamental understanding of phenomena controlling nanoparticle dispersion into the polymer matrix as well as the correlations between structure and properties of the prepared materials, including electrical conductivity, rheological properties and polymer crystallization phenomena. As the availability of graphene (i.e. a single layer of sp2 carbons) nanoflakes remains extremely limited and insufficient for the exploitation in large scale applications embedding graphene in the polymer bulk, different types of graphene-related materials were selected for exploitation in this PhD thesis, namely graphite nanoplatelets (GNP) and reduced graphene oxide (rGO). In particular, different grades of GNP and rGO were selected aiming at the correlation between their quality, mainly in terms of defectiveness and aspect ratio, and the properties of their corresponding polymer nanocomposite. For these reasons, the initial part of this thesis is focused on thorough characterization of nanoflake quality, i.e. defectiveness and aspect ratio, through electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. On the other hand, the second part is focused on the preparation and detailed characterization of nanocomposites prepared by ring opening polymerization of polyester oligomers (CBT) during melt mixing in presence of graphene-related materials. In particular, the effects of the exploitation of different graphene-related materials, of the polymerization during reactive mixing and of the processing parameters (processing temperature, time and shear rate) on the electrical and thermal properties of polymer nanocomposites is addressed. Thorough characterization of the effect of the exploitation of pristine and high temperature-annealed reduced graphene oxide on the nanocomposite properties is also reported, in terms of both of conductivities and modification in the crystallization of the polymer matrix. The results reported in this thesis demonstrate the viability of CBT polymerization during melt mixing with graphene-related materials to produce thermally and electrically conductive polymer nanocomposites aiming at possible industrial applications
De-anonymizing clustered social networks by percolation graph matching
No full textOn-line social networks offer the opportunity to collect a huge amount of valuable information about billions of users. The analysis of this data by service providers and unintended third parties are posing serious treats to user privacy. In particular, recent work has shown that users participating in more than one on-line social network can be identified based only on the structure of their links to other users. An effective tool to de-anonymize social network users is represented by graph matching algorithms. Indeed, by exploiting a sufficiently large set of seed nodes, a percolation process can correctly match almost all nodes across the different social networks. In this paper, we show the crucial role of clustering, which is a relevant feature of social network graphs (and many other systems). Clustering has both the effect of making matching algorithms more prone to errors, and the potential to greatly reduce the number of seeds needed to trigger percolation. We show these facts by considering a fairly general class of random geometric graphs with variable clustering level. We assume that seeds can be identified in particular sub-regions of the network graph, while no a-priori knowledge about the location of the other nodes is required. Under these conditions, we show how clever algorithms can achieve surprisingly good performance while limiting the number of matching errors
Reverberation time measurements in non-diffuse acoustic field by the modal reverberation time
No full textThe increasing presence of low frequency sources and the lack of acoustic standard measurement procedures make the extension of reverberation time measurements to frequencies below 100 Hz necessary. In typical ordinary rooms with volumes between 30 m^3 and 200 m^3 the sound field is non-diffuse at such low frequencies, entailing inhomogeneities in space and frequency domains. Presence of standing waves is also the main cause of bad quality of listening in terms of clarity and rumble effects. Since standard measurements according to ISO 3382 fail to achieve accurate and precise values in third octave bands due to non-linear decays caused by room modes, a new approach based on reverberation time measurements of single resonant frequencies (the modal reverberation time) has been introduced. From background theory, due to the intrinsic relation between modal decays and half bandwidth of resonant frequencies, two measurement methods have been proposed together with proper measurement procedures: a direct method based on interrupted source signal method, and an indirect method based on half bandwidth measurements. With microphones placed at corners of rectangular rooms in order to detect all modes and maximize SNRs, different source signals were tested. Anti-resonant sine waves and sweep signal turned out to be the most suitable for direct and indirect measurement methods respectively. From spatial measurements in an empty rectangular test room, comparison between direct and indirect methods showed good and significant agreements. This is the first experimental validation of the relation between resonant half bandwidth and modal reverberation time. Furthermore, comparisons between means and standard deviations of modal reverberation times and standard reverberation times in third octave bands confirm the inadequacy of standard procedure to get accurate and precise values at low frequencies with respect to the modal approach. Modal reverberation time measurements applied to furnished ordinary rooms confirm previous results in the limit of modal sound field: for highly damped modes due to furniture or acoustic treatment, the indirect method is not applicable due to strong suppression of modes and the consequent deviation of the acoustic field from a non-diffuse condition to a damped modal condition, while standard reverberation times align with direct method values. In the future, further investigations will be necessary in different rooms to improve uncertainty evaluation
Cardiovascular morphometry with high-resolution 3D magnetic resonance: first application to left ventricle diastolic dysfunction
No full textDiscovering High-Utility Itemsets at Multiple Abstraction Levels
No full textHigh-Utility Itemset Mining (HUIM) is a relevant data mining task. The goal is to discover recurrent combinations of items characterized by high prot from transactional datasets. HUIM has a wide range of applications among which market basket analysis and service proling. Based on the observation that items can be clustered into domain-specic categories, a parallel research issue is generalized itemset mining. It entails generating correlations among data items at multiple abstraction levels. The extraction of multiple-level patterns affords new insights into the analyzed data from dierent viewpoints. This paper aims at discovering a novel pattern that combines the expressiveness of generalized and High-Utility itemsets. According to a user-defined taxonomy items are rst aggregated into semantically related categories. Then, a new type of pattern,namely the Generalized High-utility Itemset (GHUI), is extracted. It represents a combinations of items at different granularity levels characterized by high prot (utility). While protable combinations of item categories provide interesting high-level information, GHUIs at lower abstraction levels represent more specic correlationsamong protable items. A single-phase algorithm is proposed to efficiently discover utility itemsets at multiple abstraction levels. The experiments, which were performed on both real and synthetic data, demonstrate the effectiveness and usefulness of the proposed approach