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Flash-Sintering of MnCo2O4 and (La, Sr)(Co, Fe)O3 Ceramics for Potential Application in SOFC
No full textThe innovative flash-sintering technique has been considered to investigate the effect of DC electric field on sintering and electrical conductivity of two oxide ceramics MnCo2O4 and La0.6Sr0.4Co0.2 Fe0.8O3 (LSCF). These oxides are renowned for their high electrical conductivity and oxygen reduction properties, and therefore find application in solid oxide fuel cell as interconnect coating and cathode respectively. Flash-sintering of LSCF composite with 10 mol% Gd doped ceria (GDC), which is considered more promising than pure LSCF for cathodic application, is also reported. In flash-sintering-effect, when an adequately high DC electric field is applied on a green specimen, which is subjected to heating at a constant rate, the field drives rapid increase in the conductivity at a suitable furnace temperature. This event drives sintering, and the rate of shrinkage is so rapid that the material, generally, sinters in a couple of seconds without requiring elevated temperature. The aim of the present work is to better understand such electric field effect on sintering as it may affect the material properties (microstructure, conductivity etc.). Till now, the technique has been mostly reported for weakly conducting or insulating materials. The present work deals with the conducting-edge materials to point out the versatility of flash-sintering technique.
The present work demonstrates the flash-sintering of conductive oxides, MnCo2O4 and LSCF. These oxides are sintered under electric field ranging from 7.5 to 12.5 V/cm at furnace temperatures 100-200°C, which are 1000°C lower than traditional heat treatments. LSCF, being highly conductive, surprisingly sinters at 25°C under 12.5 V/cm. On the other hand, the composite phases (LSCF/GDC: 60/40, 50/50 and 40/60 weight ratios) flash sinters at higher temperatures and electric fields which is systematic with GDC additions. The role of electric field and temperature in sintering is realized from specimen temperature which helps to understand the observed outstanding event. The flash-sintering occurs at conventional sintering temperatures and therefore, enhanced sintering at a particular temperature at this stage is expected to result from increased defect concentrations. Rapid increase in the conductivity possibly provides diffusion-able sites at rapid rate and the high sintering rate can be explained to occur using these sites. At drastic conductivity increase, the thermal effect is so dominant that ions diffuse for sintering more with the support of local temperature and less by the electric field. The extent of sintering is confirmed through scanning electron microscopy. The microstructural analysis carried on flash-sintered samples suggests that the surface morphology and grain growth homogeneity resemble that of traditionally-sintered samples. With the proper choice of processing parameters (electric field and current density), dense and pore-free microstructure for MnCo2O4 coating and porous microstructure of LSCF for cathodic application are obtained in very short sintering time. From the case of composites, current is clearly pointed to be a determining parameter in controlling the density. An enhanced electric field effect is recorded on the microstructure of MnCo2O4 starting at 1100°C. No such temperature discrimination is observed for LSCF, the sintering effects being regular with the temperature. From XRD analysis, MnCo2O4 undergoes to a significant phase reduction for the specimen temperature in excess of 1100°C. The LSCF and its composite phase’ are stable and compatible with GDC10 against flash-sintering. These observations are in agreement with conventional sintering. The flash-effect is investigated by analyzing electrical conductivity property of dense specimen. Consistent changes in current-voltage characteristics with temperature suggest that the electric field controls the conductivity in the same way as temperature does. At sufficient temperature, the electric field enhances the conductivity by increasing thermal excitation of charge carrier. At low temperature, the field enhances the conductivity by direct energy transfer; these temperature and field has a fundamental role in flash-sintering. On the basis of conductivity analysis, flash-sintering is proposed to be accelerated by utilizing defect complexes formed during the “polaron-hopping” which is the usual conduction mechanism of these materials, MnCo2O4 and LSCF. On the basis of correlation between the microstructure and phase stability, a constraint about the utilization of defect complex is realized. Sintering is enhanced when there is stabilization of reduction reaction in hopping process. This condition assures the availability of defect complexes for sintering; under equal probability of hopping transitions, the reduction is more under the tendency of oxidation. It was realized in the sintering of MnCo2O4 is enhanced over conventional for temperatures higher than 1080°C which corresponds to the reduction temperature. Such implication was verified on LSCF where sintering is found to be enhanced for all the considered temperatures as it undergoes reduction as sintering starts. Therefore, sintering is proposed to occur by the movement of reduced transition metal cations during usual hopping mechanism. Sintering at unusually low temperatures, in very short times and involving quite usual ionic transitions shows its potentials for ceramics manufacturing especially in multilayer production and temperature sensitive application
L'Antiope di Euripide
No full textIl presente lavoro si propone come un commento all'Antiope di Euripide. Dopo una rapida analisi delle testimonianze letterarie ed iconografiche che ci parlano delle vicende portate sulla scena, si è proposta una ricostruzione della trama della tragedia. A questa sezione fa seguito un'analisi puntuale dei singoli frammenti. Particolare attenzione è dedicata all'agone tra Amfione e Zeto, l'episodio che pare aver goduto in antico di maggior fortuna; per questa sezione si è proposta un'analisi di temi e problemi dibattuti dai due personaggi, anche in rapporto ad analoghe riflessioni riscontrabili in testi cronologicamente prossimi
Hydrodynamics of Gravel Bed Flows (Implication on Colmation)
No full textBottom of the mountainous rivers is generally composed of natural gravels. Flow depth in such rivers is generally shallow, with the ratio of water depth to size of bed materials (known as relative submergence) rarely higher than 20. In this type of flow, gravels intrusion induces significant spatial variation of the flow characteristics near bed region, which is known as roughness layer. The simultaneous effects of natural gravels and water surface cause formation of complicated flow structure which is to some extent different from the flow with high relative submergence (flow with relative submergence higher than 40). Despite abundance of studies in shallow flows, there are only a limited number of studies concerning spatial organization of near bed flow field for such type of flow, with also contradictory results. The spatial organization of near bed turbulent flow characteristics is also important for transport of fine sediment. Transport of fine sediments is generally correlated to the asymmetry of vertical velocity. Asymmetry of vertical velocity also arises from a quasi-cyclic process of upward motion of low-velocity fluid parcels (ejection) and downward motion of high-velocity parcels (sweep), together known as bursting process. Spatial organization of bursting process and asymmetry of vertical velocity in near bed and respect to bed topography has not been inscribed properly.
In heterogeneous flows, the use of spatially averaged turbulent transport equations, known as Double Averaged Navier-Stikes equations (DANS), is common. In DANS equations viscous drag, form drag and correlation of spatial fluctuation of time averaged velocities (known as form induced stresses) are explicitly expressed. Despite prevailing usage of DANS equations in study of gravel bed flow, examination of vertical velocity has not been performed appropriately by applying double averaging method. Also, the role of form induced stresses in vertical momentum flux has not been highlighted. In present thesis, Stereoscopic Particle Image Velocimetry at near bed horizontal layer and Digital Particle Image Velocimetry in vertical planes are employed together with laser scanning of bed elevations to study flow field and turbulence structure over a coarse immobile gravel bed in submergence conditions ranges from 5 to 10. Spatial organization of flow characteristics at the near bed region is analyzed respect to bed topography. This analysis is also composed of spatial distribution of bursting process and vertical momentum flux. Moreover, vertical profiles of double averaged turbulent flow characteristics and form induced stresses with different relative submergences are compared.
Results show that near bed flow field is characterized by a strip structure induced by secondary currents. Such structure tends to be disrupted by the effect of gravel protrusions. To better analyze the interaction between the flow field and gravel bed protrusions, cross-correlations of different velocity components and bed elevations in a horizontal layer just above gravel crests are computed. These results show that upward and downward flows occur not randomly on the bed, but in correspondence to upstream and downstream side of gravels. Also, turbulent momentum flux is directed downward in the downstream side of gravel crests and it is directed upward in upstream side of gravel crests. This is due to prevalence of ejection and sweep events respectively in upstream and downstream sides of gravel crests. These results are in agreement with formation of separation and reattachment zones around gravel crests. Moreover, spatial distribution of sweep and ejection events are organized in streamwise elongated strips with high and low values which are consistent with presence of secondary currents cells. Results obtained by double averaging method show that relative submergence affects the normalwise double averaged turbulence intensity profiles all along the flow depth, while only a weak effect, limited to the near bed region, is noticed on streamwise double averaged turbulence intensity profiles. Logarithmic law parameterization of double averaged velocity profiles shows that parameters change considerably with relative submergence and, in some cases, no clear log-law region was found. These results challenge application of log-law in such type of flow. Analysis of the vertical velocity shows that far from the bed, vertical turbulence momentum flux is upward, while below gravel crests it is downward. This behavior is resulted by prevalence of ejection events far from the bed and sweep events below gravel crests. Results show that vertical momentum flux resulted by form induced component is not significant, except below gravel crests which are upward in to the water column. A limited number of qualitative observations in the real case of fine sediments presence in the matrix of rough bed is in agreement with the results of turbulent flow characteristics. Sand ribbons are clearly formed due to secondary currents. Also, fine materials are mostly deposited and eroded respectively in downstream and upstream sides of gravel crests. The results of present study show that in general some regions actively participate in transport, while the other regions do not participate in the transport. From this basis, Rouse criterion has been developed by considering spatial variation of vertical momentum flux
Static and dynamic properties of spin-orbit-coupled Bose-Einstein condensates
No full textThe recent realization of synthetic spin-orbit coupling represents an outstanding achievement in the physics of ultracold quantum gases. In this thesis we explore the properties of spin-orbit-coupled Bose-Einstein condensates with equal Rashba and Dresselhaus strengths. These systems present a rich phase diagram, which exhibits a tricritical point separating a single-minimum phase, a spin-polarized plane-wave phase, and a stripe phase. In the stripe phase translational invariance is spontaneously broken, in analogy with supersolids. Spin-orbit coupling also strongly affects the dynamics of the system. In particular, the excitation spectrum exhibits intriguing features, including the suppression of the sound velocity, the emergence of a roton minimum in the plane-wave phase, and the appearance of a double gapless band structure in the stripe phase. Finally, we discuss a combined procedure to make the stripes visible and stable, thus allowing for a direct experimental detection
Lo statuto giuridico della bioinformazione tra biobanche di ricerca e fascicolo sanitario elettronico
Get PDFLa tesi individua ed esplora in prospettiva comparata i profili privatistici che vengono in rilievo con riferimento alla gestione della bioinformazione,nel contesto tecnologico delle biobanche di ricerca e del fascicolo sanitario elettronic
'...And suddenly the memory revealed itself'. The role of IT in supporting social reminiscence
No full textEvery human being is familiar to the experience of reminiscence: recalling and revisiting our past memories. We reminisce to create our identities. We reminisce to maintain our relationships. We reminisce to review our lives. And we also reminisce together. This dissertation develops around the topic of how IT stimulates reminiscence, motivated by its proven benefits in peopleâs well-being and its prevalence across all stages of life. The focus is set on older adults, with the overall goal of fostering intergenerational social interactions (that is, interactions between older adults and younger generations). This thesis is motivated by the current interest on active ageing as an emergent way of life, with better and more opportunities for health, participation and security. As the world ageing population continues to increase and the average life expectancy of people increasing every year, there is a growing need for understanding the ageing phenomena, and particularly, for designing human centered information technologies (IT) that enhance opportunities of social participation as people age. Within this scenario, this dissertation addresses the following research questions using a participatory approach to research and design: (i) what is the role of IT in enabling a more happy and active ageing?; (ii) in doing so, how can IT stimulate intergenerational social interactions?, and (iii) can IT-supported social reminiscence facilitate these interactions and make of them an enjoyable experience?. To answer these questions, we leverage upon a participatory action research approach to gain an understanding of the topic, moving later to the participatory design of IT for social reminiscence and finally, evaluating how IT supports the practice of social reminiscence in a face-to-face intergenerational context. The contributions of this dissertation can be summarized as follows:
- Knowledge: an understanding of what role IT can play in supporting, stimulating and accompanying active ageing and social interactions through the practice of reminiscence.
- Model: a conceptual model of the different stages of IT-supported social reminiscence sessions, and an extended model of the design spaces for intergenerational engagement.
- System: an exemplary socio-technical system that fits the aforementioned roles, including a knowledge base and algorithms to support contextual stimulation of reminiscence, using multimedia resources that are publicly available on the web.
- Evaluation: quantitative and qualitative results obtained from observing the use of our system in a real intergenerational context
Getting the job doneâ¦!? (Professional) challenges on the frontline of Public Employment Services in Vienna and Milan
No full textIndividualised activation services have gained in importance in all European welfare states making lower level discretion an intrinsic feature of activation policies. Thus, the debate on activation policies and challenges to social citizenship has to go beyond formal policy and to take into account also its operational and street-level dimension which shapes what is eventually produced as policy on the ground. In this context, frontline practice plays a crucial role since it constitutes the very moment where activation policies encounter their target groups and real world solutions have to be found.
This PhD project is aimed at exploring the challenges, interpretations and reactions of frontline workers in activation services and at analysing them in the light of a combined theoretical framework which understands frontline practice as part of the policy making chain and addresses issues such as the use of discretion, power and situated agency.
The research project consists of an explorative qualitative study undertaken at the frontline of Public Employment Services in the cities of Vienna (Austria) and Milan (Italy). The findings contribute to the debate on constraints and possibilities for âactivation workâ as a practice of citizenship in a field whose challenges are often neglected both by social policy and social work research, although it has become a central arena for welfare state intervention and, eventually, for the realisation of social citizenship. Particular attention is given to the questions whether and to what extent professionalising âactivation workâ could counteract the precarious and highly individualised role of frontline workers in this ambiguous public domain
Study of Timber-frame Building Seismic behaviour by Means of numerical modelling and Full-scale shake table testing
No full textThis thesis regards the study of the seismic behaviour of timber-frame buildings. Three are the main sections. Firstly, the study of the linear and non-linear behaviour of a timber-frame wall subjected to a horizontal force is presented, suggesting some analytical expression to correlate the mechanical behaviour of the entire wall to the mechanical properties of connection devices (i.e. fasteners, angle brackets and hold-down). Particular attention was paid to the ductility of each component. Secondly, a numerical modelling for the seismic linear analysis of multi-storey walls is proposed. In this section the horizontal force distribution between the walls is investigated too. Thirdly, a full-scale shake table test on a prefabricated 3-storey timber-frame building is described
Multiple Tasks are Better than One: Multi-task Learning and Feature Selection for Head Pose Estimation, Action Recognition and Event Detection
No full textComputer vision is a field that includes methods for acquiring, processing, analyzing, and understanding images and videos and, in general, high-dimensional data from the real world in order to produce numerical or symbolic information. The classical problem in computer vision is that of determining whether or not the image or video data contains some specific object, feature, or activity. This task can normally be solved robustly and without effort by a human, but is still not satisfactorily solved in computer vision for the general case - arbitrary objects in arbitrary situations. The existing methods for dealing with this problem can at best solve it only for specific objects, such as simple geometric objects (e.g., polyhedra), human faces, printed or hand-written characters, or vehicles, and in specific situations, typically described in terms of well-defined illumination, background, and pose of the object relative to the camera.
Machine Learning (ML) and Computer Vision (CV) have been put together during the development of computer vision in the past decade. Nowadays, machine learning is considered as a powerful tool to solve many computer vision problems. Multi-task learning, as one important branch of machine learning, has developed very fast during the past decade. Multi-task learning methods aim to simultaneously learn classification or regression models for a set of related tasks. This typically leads to better models as compared to a learner that does not account for task relationships. The goal of multi-task learning is to improve the performance of learning algorithms by learning classifiers for multiple tasks jointly. This works particularly well if these tasks have some commonality and are generally slightly under-sampled
Semplified seismic Vulnerability Assessment of Masonry Arch Bridges
No full textThis study concerns seismic vulnerability assessment of masonry arch bridges with common typologies in Europe. Bridges are, in most cases, the most vulnerable elements in the transportation network during an earthquake; therefore, their seismic vulnerability assessment is necessary for a proper planning of the emergency phase and to define a priority for retrofit interventions. Masonry arch bridges were subdivided into homogeneous classes of single span and multi-span structures, according to the result of a statistical analysis made up of a large stock of 757 railway bridges located in high seismic areas.
All the different collapse mechanisms for seismic action were studied for each class of masonry arch bridges with application of limit analysis and the calibration with FEM. In particular, limit analysis methods for the seismic assessment of single and multi spans bridges were developed. A innovative limit analysis approach was proposed for the assessment of the global transverse seismic capacity of multi-span masonry bridges with slender piers. Envelope curves representing the seismic capacity expressed in terms of limit horizontal acceleration were derived by parametrical analysis by means of simplified limit analysis. These curves can be used for a simplified vulnerability assessment of masonry arch bridges and for a simple calibration of the judgment obtained by BMS through inspection visits to bridges. In the second part of the study, a new simplified approach for the fast calculation of seismic fragility curves of numerous masonry arch bridge clusters is proposed. The aim of this thesis is to propose a quickly procedure to estimate the seismic vulnerability of extended roadway and railway bridge networks in emergency conditions and to optimize the retrofit interventions