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Mechanics of dry granular flows driven by gravity
No full textDry granular flows are an important paradigm for a large number of problems, from industrial applications to geophysical events. Most of the research published has
studied inclined granular flows over bumpy and at rigid base, while only few of them have been focused on fully developed steady flows over an erodible beds. This kind of flows are important to understand the dynamics of complex phenomena such as dense snow-avalanches and landslides, whose rheology is still ambiguous and not well defined. In this thesis, we focus on the following three aspects: (1) dynamics of uniform flows over loose bed, where the condition of uniformity and steadiness has accurately checked, (2) the influence of collisional parameters on the behavior of the flow, (3) the side-wall effect. Experimental investigations were carried out in laboratory through imaging techniques and direct methods to analyze the stresses exerted by the flow. The thesis contributes with accurate measurements of the mean velocity, solid concentration, and granular temperature pro files obtained along the depth and the free surface of the flow. Considerations have been derived in comparison to the existing data, pointing out the importance of collisional parameters and the conditions for uniform and steady flows. Experimental evaluation of the stresses was carried out at the side-walls of the channelized granular flows by the means of new device developed in the laboratory and tested for different con figurations of the flow
Measuring, Understanding, and Estimating the Influence of the Environment on low-power Wireless Networks
No full textAfter a decade and a half of research in academia and industry, wireless sensor networks (WSNs) are seen as a key infrastructure able to monitor the environment in which they are immersed, thanks to their miniaturization, autonomy, and flexibility. Still, outdoor deployments of WSNs (e.g., in forests) are notoriously difficult to get right, partly due to the fact that their low-power wireless communication is greatly affected by the characteristics of the target environment (e.g., temperature, humidity, foliage). In the absence of quantitative evidence about the target application environments, the asset that drives a successful and reliable outdoor deployment is the experience gained from previous deployments, lab-like testbeds, or simulators that however often do not resemble the real-world environments. The general goal of this dissertation is to support the principled design and deployment of WSNs by improving the understanding of how the natural outdoor environment affects the network stack, and providing tools and modeling techniques to address this impact.
This constitutes the premise for WSNs to be a credible tool for domain experts (e.g., biologists) operating in this field. Our own practical need to design and deploy a reliable WSN system for wildlife monitoring in the mountains near Trento, Italy, pushed our goals towards a deployment and application oriented perspective, whose ultimate objectives are: supporting the WSN deployment; informing the selection or design of protocols, to ensure they are well-suited to the target environment; deriving models to push the envelope of what can be predicted or simulated beforehand. To achieve these goals we must start from the first step—assessing quantitatively the characteristics of the low-power wireless links in-field, i.e., in the environment where the WSN must be deployed. To this end, we contribute with Trident and Harpoon, tools for in-field connectivity and routing performance assessment that support principled, repeatable, automated, and flexible collection of measurements in the target environment without the need for a tethered infrastructure and without requiring coding from the end user. Then, using these tools we collect a large set of data traces from six campaigns across different years, environments and seasons, whose analysis quantified the impact of the environmental factors on the network stack, focusing primarily on the physical and routing layers. Finally, we exploit the data traces to create models for both estimating the link quality at run-time and reproducing realistic network conditions in simulators.
We argue that the tools we expressly designed for gathering in-field empirical traces, the understanding and quantitative characterization of data traces from real environments, and the modeling, together significantly advance the state of the art by rendering the process of designing and deploying a WSN more repeatable and predictable
Integrating artificial with natural cells
No full textPrevious attempts to control cellular behavior were mainly based on genetic engineering. While useful, such an approach suffers from several complications. Living cells grow and evolve which could lead to modifications of the engineered circuits, causing not only the loss of their functions but also an altering of the environment. However, other methods are possible. All living cells can naturally sense and respond to their environment and to each other. Thus, artificial, non- living cells can be engineered to activate already existing natural cellular pathways. In this way, the genetic engineering component moves from the natural to completely artificial, laboratory-made cells. Moreover, synthetic systems operating in living organisms also depend on elements with unknown function, leaving many gaps in the understanding of how living cells work. Building life- like systems with non-living components could help reveal unrecognized but necessary cellular mechanisms. However, the design of functional, genetically encoded cell-free systems is difficult, because biological parts have been evolved to function optimally inside of living cells. In vitro conditions are different.
First, some practical rules for the construction of functional synthetic circuits in vitro were defined. The Influences of the organization of genetic elements within a synthetic operon on protein expression levels were studied and optimal sequence compositions and lengths between genes to assemble genetic circuits were found. Then, artificial cells that can control the behavior of living systems were built. The artificial cells were able to sense a molecule that Escherichia coli cannot sense on its own and translate that molecule into a chemical message that E. coli can sense and respond to. The natural sensing of E. coli was expanded without genetically modifying the bacteria. Finally, to better integrate artificial with natural cells, a complete communication pathway was constructed. Bacteria speak to each other by quorum sensing. Such mechanisms mediate cell-cell communication among bacteria and regulate several cell density related processes, such as virulence. Various synthetic quorum sensing mechanisms were constructed in vitro within artificial cells. Artificial cells able to sense the presence of living cells were built. In addition, the artificial cells were capable to synthesize quorum sensing molecules for E. coli, Vibrio harveyi, Vibrio fischeri and Pseudomonas aeruginosa. When integrated together, artificial cells successfully mediated interspecies communication with natural cells. Such artificial systems could be useful as therapeutic tools to defeat pathogenic infections. Moreover, the achievement of such functions represents a new way to better understand the potential of the artificial cells to mimic cellular life
L'insediamento rurale in Africa Proconsularis, Tunisia (regione di Thugga) e Algeria (Parc National d'El Kala), in età romana e tardo-antica
No full textIl confronto è un procedimento fondamentale per poter meglio comprendere i dati provenienti dai progetti di ricognizione archeologica. Partendo da questo presupposto, il presente studio si pone l'obbiettivo di approfondire la conoscenza dei modelli di sfruttamento del paesaggio agrario antico attraverso il confronto tra due territori, rispettivamente in Tunisia attorno a Thugga ed in Algeria nella wilaya di El Tarf. Si procederà, attraverso l'applicazione di analisi statistiche (bi-variate e multi-variate), alla ricerca di eventuali modelli preferenziali di insediamento e di relazioni tra siti, basandosi anche sulle stime della capacità di produzione dei torchi oleari e la conseguente possibile estensione del fondo agricolo
Exploiting Online User Feedback in Requirements Engineering
No full textUser feedback is mainly defined as an information source for evaluating the customers’ satisfaction for a given goods, service or software application. Due to the wide diffusion of the Internet and to the proliferation of mobile devices, users access a myriad of software services and applications, at any time and in any place. In this context users can provide feedback upon their experience in using software, through dedicated software applications or web forms. This
online user feedback is a powerful source of information for improving the software service or application.
Specifically in software engineering, user feedback is recognized as a source of requests for change in a system, so it can contribute to the evolution of software systems. Indeed, user feedback is gaining more attention from the requirements engineering research community, and dedicated buzzwords have been introduced to refer to research studies in RE, i.e. mass RE and
crowd RE.
Arguing on this premise, the possibility of exploiting user feedback is worth to be investigated in requirements engineering, by addressing open challenges in collection as well as in the analysis of online feedback. The research work described in this Thesis starts with a stateof-the-art literature analysis that revealed that the definition of user feedback as an artifact, as
well as the characterization and understanding of its process of elaboration and communication were still unexplored, especially from the requirements engineering perspective.
We adopted a multidisciplinary approach by borrowing concepts and techniques from ontologies,
philosophy of language, natural language processing, requirements engineering and human computer interaction. The main research contributions are: an ontology of user feedback, the characterization of user feedback as speech acts for applying a semantic analysis, and the proposal of a new way of gathering and filtering user feedback by applying an argumentation framework
Influence of reward history on visual working memory representations
No full textReward is a strong determinant of human and non-human behavior, influencing the exploration of the world around us and our interactions with it. Interestingly, the impact of reward and reward-associated objects is not limited to strategic changes in approach behavior or attention deployment, but also extends to situations in which prioritizing processing of such objects is not necessarily advantageous for current goals. In spite of converging evidence for the automatic influence of reward on attentional deployment, less is known about the impact of reward on other cognitive processes.
In this thesis I describe a first attempt to investigate the influence of reward in encoding and maintenance of visual representations in working memory. Throughout this thesis I argue that once objects have been associated with a positive outcome in past encounters, they are preferentially encoded and maintained in visual working memory (VWM) even when reward is no longer provided or when there is no consistent pairing between reward feedback and target identity. In Chapters 2 and 3 I demonstrate that reward associated objects interfere with the visual representations of less valuable items maintained in VWM. This interference was already present starting 10 ms from the offset of the memory display suggesting that valuable objects directly affected the encoding of less valuable items. This robust phenomenon was observed at different delays, both when reward-associated objects were task-relevant and when they were not, and was independent of object salience. However, the interference disappeared when task requirements for target selection increased suggesting that items with a positive reward history can effectively capture attention and interfere with VWM representations only when cognitive resources are not exhausted by the main task (Chapter 3).
In the last study presented in this thesis I explored the possibility that reward could impact VWM beyond target selection and encoding, namely influencing the active maintenance process. To investigate this hypothesis I measured reward priming effects on event-related potential (ERP) indices of selective attention – the N2pc - and visual working memory maintenance – the CDA (contralateral delay activity). Results indicate that reward modulated CDA only, speaking for a discrete effect of reward on VWM maintenance. While the precise nature of such modulation is still unknown, these results suggest that reward history might influence the precision or the duration of visual representations maintained in VWM. Further studies are necessary to directly test this hypothesis, but these initial results suggest an interesting direction for future research in better characterizing the nature and extent of the influence of reward history on visual cognition
Experimental Perspectives on Intergenerational Altruism: A Study on Public Good Dilemmas
No full textHumans evolved over millennia into agents that invest heavily, both directly and indirectly, in their children. Part of the investment into children is represented by contributions to long-run public goods, including the educational system, the health-care system, major infrastructures and environmental protection. Moreover, the production of some of these public goods has wide-ranging externalities to local or global communities (think of vaccination programs, for example). This Doctoral Thesis is a collection of three essays on the topic of long-run, across-the-border public goods, from the vantage point of Experimental and Behavioral Economics. The first Chapter reviews the literature up to date, re-organizing previous works on Public Good games for the benefit of explaining why intergenerational and international public goods are different from standard ones. The second and third Chapters provide empirical evidence on matters such as heterogeneity linked to seniority and dynastic membership in the provision of public goods
Performance Optimisation of Dielectric Elastomer Generators
No full textA Dielectric Elastomer Generator (DEG) is an electromechanical transducer, basically a highly deformable parallel-plate capacitor, made up of a soft DE membrane coated with two compliant electrodes on its opposite surfaces. This device is able to convert
mechanical work, emanating from its interaction with the environment, into electrical energy. The capacitance depends on the deformation undergone by the membrane, and
its variability can be exploited to extract electric energy by (i) initially stretching, (ii)
then charging the capacitor, (iii) subsequently releasing the stretch and finally (iv) harvesting the charge at a higher electric potential.
The optimisation procedure for a load-driven soft planar DEG is presented, assuming hyperelastic and ideal dielectric behaviour. The DEG undergoes the ideal four-stroke electromechanical cycle previously described and its performance is evaluated on the basis of the energy extracted during a cycle and of the efficiency, defined as the ratio of the harvested energy on the total invested energy. The amount of extracted energy is limited due to possible failures of the device, which are, in the most general case, electric breakdown, material rupture, buckling-like instabilities due to loss of the tensile stress state and electromechanical instability. These failure mechanisms determine the allowable state region for the generator. Hence, in order to identify the best cycle that complies with these limits, a constrained optimisation problem is formulated and the generator performance is estimated. For the different loading cases examined, namely equibiaxial stress state and plane strain, numerical results show, as expected, a critical dependence of the harvested energy on the ultimate stretch ratio and, against expectations, a universal limit on the dielectric strength of the DE membrane beyond which the optimal cycle is independent of this parameter. Thus, there is an upper bound on the harvested energy, which depends only on the ultimate stretch ratio. In addition to the simple parallel-plate configuration, an annular DEG deforming out-of-plane has been analysed. In this configuration the generator is made up of an annular membrane constrained at the boundary by a rigid ring and at the centre by a rigid plate, on which an external force is applied. Due to the loading, the membrane deforms non-homogeneously out-of-plane. In order to avoid loss of the tensile stress state, electric breakdown and electromechanical instability, the applied voltage is controlled, thereby limiting the maximum voltage and keeping the maximum stretch in an admissible range.
Numerical results show that the prestretch of the membrane is crucial for an effective behaviour of the device. In fact, the unprestretched generator performs poorly with regard to both energy and efficiency. A small prestretch, of approximately 5%, ensure a sixfold improvement in the gained energy and a fivefold increment in efficiency. The performance of the generator is evaluated for different values of the applied load and of the prestretch. This analysis shows that increasing the applied force the harvested energy increases monotonically, while the efficiency increases until a peak value and then decreases. Hence, for an out-of-plane DEG, the choice of the applied force is decisive to ensure a good trade-off among energy and efficiency. Moreover, a comparison of different DEG layouts demonstrates that the annular DEG can compete with the equibiaxial planar generator, in terms not only of efficiency, but also of harvested energy. What has been so far pointed out is valid under the hypothesis of ideal, lossless material. Since polymers are affected by time-dependent effects, this hypothesis appears to be not completely realistic. Indeed, a predicting model for soft dielectric elastomer generators must include a realistic model of the electro-mechanical behaviour of the elastomer filling, the variable capacitor and of the electrical circuit connecting all the device components. To this end, the ideality assumption of the material and of the cycle
has to be removed. Hence, a complete framework for a reliable simulation of soft energy harvesters is proposed for a soft viscous dielectric elastomer generator, operating in an electrical circuit for energy harvesting and subjected to a periodic mechanical stretch. The electrical model of the generator takes into account the effects of the electrodes and of the conductivity current through the dielectric material. A phenomenological electro-viscoelastic model at large strain is proposed and calibrated on the basis of experimental data available in literature for a polyacrylate elastomer (VHB-4910). The effects of
viscoelasticity and of possible changes of the permittivity with strains on the generator performance are hence investigated. Numerical results underline the importance of time-dependent effects on the evaluation of the generator performance. The main outcome of this analysis is that, compared with a hyperelastic model, the efficiency is reduced by viscoelasticity for high values of the mean stretch and of the amplitude of stretch oscillation. The reduction is almost insensitive of the mechanical frequency while the efficiency is further reduced by the variation of the permittivity with strain. Moreover, viscoelastic effects modify the allowable state region of the generator. At regime condition, the failure curves relative to electromechanical instability and to loss of the tensile stress state are strongly modified by the viscous effects. This fact results in the alteration of the allowable state region of the generator. Furthermore, due to the change in shape and size of the admissible region under this condition, a more surprising result is the fact that the natural configuration is a not-allowed state. As a consequence, there is an upper bound on the maximal stretch oscillation amplitude. Focusing on the main features of the electrical circuit, an important outcome of the analysis is the identification of a value range of the external electric load for which the efficiency is maximal. Furthermore, the viscous dissipation of the material dominates the energy
loss arising from the leakage current across the dielectric membrane
Semantic Enrichment of Mobile Phone Data Records Exploiting Background Knowledge
No full textEvery day, billions of mobile network log data (commonly defined as Call Detailed Records, or CDRs) are generated by cell phones operators. These data provide inspiring insights about human actions and behaviors, which are essentials in the development of context aware appli- cations and services. This potential demand has fostered major research activities in a variety of domains such as social and economic development, urban planning, and health prevention. The major challenge of this thesis is to interpret CDR for human activity recognition, in the light of background knowledge of the CDR data context. Indeed each entry of the CDR is as- sociated with a context, which describes the temporal and spatial location of the user when a particular network data has been generated by his/her mobile devices. Knowing, by leveraging available Web 2.0 data sources, (e.g., Openstreetmap) this research thesis proposes to develop a novel model from combination of logical and statistical reasoning standpoints for enabling human activity inference in qualitative terms. The results aimed at compiling human behavior predictions into sets of classification tasks in the CDRs. Our research results show that Point of Interest (POI)s are a good proxy for predicting the content of human activities in an area. So the model is proven to be effective for predicting the context of human activity, when its total level could be efficiently observed from cell phone data records
Question of status in the European Union. The space between immigration and citizenship.
No full textPlurality in Unity is a simple but effective formula to summarise the current situation of individual status in Europe. Multiple and variable over time are the status
possessed, or that could be acquired, by persons, although, in this composite panorama, it is still nationality that appears to be the most valuable, privileged and secure status: the one capable to reduce to unity all the others. However, if this remains true in general terms, the continuous appearance of new status and the transformation of the European Union itself into a rights provider, has challenged not only the hegemony of nationality, as the sole meaningful status for mobile persons, but, inevitably, has also shaped and modified its content and symbolic meaning in
accordance with the evolved context. This thesis concentrates upon the relation between immigration and citizenship legislations at the supranational, national and sub-national level, since they are the basis and the determinants of individual status in relation to a certain territory. Firstly, it focuses on the relation between individual status in the EU legal order, i.e. on the status attributed by EU laws to third-country nationals labour migrants, and on the Union citizenship. In the second part, it investigates the range of status available to non-nationals within Belgium, paying particular attention to the sub-national level; Sweden, considering the influence of the Nordic cooperation; and, finally, Switzerland as regards, specifically, the role of sub-national units in citizenship
acquisition procedures and influence on the government of immigration of the Swiss-EU relations as regards persons' freedom of movement. This thesis concludes affirming that an increasing level of interaction, reciprocal influence and convergence are observable in the government of immigration and citizenship acquisition. The latter is increasingly used as a tool to better govern the former, by relying on the everlasting distinction between the citizens and the others,
and regardless of the level of government considered