1731 research outputs found
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Graded Lie algebras of maximal class in characteristic p, generated by two elements of degree 1 and p
No full textLie algebras of maximal class (or filiform Lie algebras) are the Lie-theoretic analogue of pro-p-groups of maximal class. In particular, they are 2-generated. If one further assumes that the algebras are graded over the positive integers, then over a field of characteristic p it has been shown that a classification is possible provided one generator has
degree 1 and the other has either degree 1 or 2. In this thesis I give a classification of graded Lie algebras of maximal class with generators of degree 1 and p, respectively
Modeling and Querying Data Series and Data Streams with Uncertainty
No full textMany real applications consume data that is intrinsically uncertain and error-prone. An uncertain data series is a series whose point values are uncertain. An uncertain data stream is a data stream whose tuples are existentially uncertain and/or have an uncertain value. Typical sources of uncertainty in data series and data streams include sensor data, data synopses, privacy-preserving transformations and forecasting models.
In this thesis, we focus on the following three problems: (1) the formulation and the evaluation of similarity search queries in uncertain data series; (2) the evaluation of nearest neighbor search queries in uncertain data series; (3) the adaptation of sliding windows in uncertain data stream processing to accommodate existential and value uncertainty.
We demonstrate experimentally that the correlation among neighboring time-stamps in data series can be leveraged to increase the accuracy of the results. We further show that the "possible world" semantics can be used as underlying uncertainty model to formulate nearest neighbor queries that can be evaluated efficiently. Finally, we discuss the relation between existential and value uncertainty in data stream applications,
and verify experimentally our proposal of uncertain sliding windows
Involving Domain Experts in the construction of OWL ontologies: experience oriented and tool base support for template-based modelling and knowledge reuse
No full textCurrent ontology engineering methodologies and tools follow an iterative ontology authoring approach where Knowledge Engineers gather the requirements for the ontology from the Domain Experts interpret them and add them to the ontology. Domain Experts can verify, validate or suggest revisions in the ontology. The recent increase in popularity of lightweight OWL (Web Ontology Language) ontologies has created the need for faster, more agile and effective methods to support the task of ontology creation. This need is testified by efforts that focus on enabling Domain Experts to better participate in the process of ontology construction, making them able not only to provide domain knowledge to Knowledge Engineer but also to directly contribute to the editing of certain parts of the ontology.
The contribution of this dissertation is threefold. In the first part of this dissertation, we investigate how to reuse already formalised knowledge, such as foundational, core, and domain specific ontologies, to support the construction of templates for the enterprise modelling domain. Templates are a popular strategy for involving Domain Experts in ontology authoring but a typical problem with this approach is that Knowledge Engineers have to create them from scratch every time they face a new modelling scenario. Libraries of reusable templates can help the work of Knowledge Engineers and support Domain Experts in providing their domain knowledge. We report our findings and lesson learned both from the concrete experience of building the templates and from a survey carried out for their evaluation. The second contribution of this dissertation is the reuse of already formalised knowledge to enrich domain specific taxonomies with knowledge involving relations by means of restriction axioms. In this contribution, at first we have presented a skeleton of a very general method called GENERATOR (Guided entity reuse and class expression generator). Second, a specific instantiation of GENERATOR, called FORZA (Foundational Ontology and Reasoner-enhanced axiomatiZAtion), for the reuse of knowledge contained DOLCE-lite and mereoTopoD is defined. As a final contribution of this dissertation, we present an approach based on Decision Diagrams or a Question-Answering (QA) system to choose the most appropriate category from a reference model (ontology or reference schema) without being exposed to the model itself. This contribution is instantiated in two different Decision Diagrams. The first one for the selection of the most appropriate template among the ones developed for the enterprise modelling scenario, and the second one for choosing the most appropriate DOLCE-lite category to support the FORZA method. As a proof-of-concept, implementation of FORZA and templates has been integrated with the MoKi ontology development environment
Empirical Methods for Evaluating Vulnerability Models
No full textThis dissertation focuses on the following research question: “how to independently and systematically validate empirical vulnerability models?”. Based on the survey of past studies about the vulnerability discovery process, the dissertation has pointed out several critical issues in the traditional methodology for evaluating the performance of vulnerability discovery models (VDMs). Such issues did impact the conclusions of several studies in the literature. To address such pitfalls, a novel empirical methodology and a data collection infrastructure are proposed to conduct experiments that evaluate the empirical performance of VDMs. The methodology consists of two quantitative analyses, namely quality and predictability analyses, which enable analysts to study the performance of VDMs, and to compare them effectively.The proposed methodology and the data collection infrastructure have been used to assess several existing VDMs on many major versions of the major browsers (i.e., Chrome, Firefox, Internet Explorer, and Safari). The extensive experimental analysis reveals an interesting finding about the VDM performance in terms of quality and predictability: the simplest linear model is the most appropriate one for predicting vulnerability discovery trend within the first twelve months since the release date of browser versions; later than that, logistic models are more appropriate.
The analyzed vulnerability data exhibits the phenomenon of after-life vulnerabilities, which have been discovered for the current version, but also attributed to browser versions out of support – dead versions. These vulnerabilities, however, may not actually exist, and may have an impact on past scientific studies, or on compliance assessment. Therefore, this dissertation has proposed a method to identify code evidence for vulnerabilities. The results of the experiments show that a significant amount of vulnerabilities has been systematically over-reported for old versions of browsers. Consequently, old versions of software seem to have less vulnerabilities than reporte
Discrezionalità e condizionamento organizzativo nella pratica professionale di servizio sociale
No full textIl lavoro affronta il tema delle tensioni fra organizzazione e professione nel servizio sociale; il frame teorico di riferimento utilizzato é quello delle "street level bureaucracies" elaborato da Michael Lipsky (1980).
Nella tesi viene evidenziato come la discrezionalità degli assistenti sociali possa essere fortemente condizionata dalle pressioni e dalle priorità organizzative grazie ad una strategia dissimulatamente managerialistica ("Power. A radical view" Lukes, 1973).
In particolare, in uno studio di caso realizzato all'interno di un servizio sociale territoriale genovese, si delinea come gli operatori possano essere indotti a mettere in atto pratiche di razionamento degli interventi a causa della carenza di risorse umane e finanziarie. Tutto ciò coerentemente con l'impostazione teorica di Lipsky.
In termini di politiche d welfare emerge come un servizio, a prescindere dalla sua impostazione universalistica, possa lentamente ridimensionarsi - in riferimento al lavoro con i minori - in una child protection agency, rinunciando tendenzialmente ad interventi secondo una logica preventiva e promozionale
Standardizing ICT for Development: Towards the Definition of a Standard Process and Maturity Model for ICTD Projects
No full textThe use of ICTs to stimulate socio-economic development has significantly grown in popularity in the recent years and has been boosted by the “mobile revolution” of the last decade. Despite the multi-year experience of academics, donor agencies and businesses, the failure rate of ICT for Development projects is still very high, resulting in a significant waste of resources. The multiple challenges that must be faced simultaneously in these projects make them more difficult than “traditional” ICT projects and recommendations such as best practices to face them have been suggested over the years. Nonetheless, the systematic replicability of these practices has never been addressed and project management and formalized development processes that address the particular challenges of the domain are extremely rare. This thesis presents a Maturity Model derived from the experience of researchers and practitioners, collected through an extensive literature review and interviews, that aims at providing a set of guidelines to be used throughout an ICT for Development intervention to increase the probability of success
Cu2ZnSnS4 thin films solar cells: material and device characterization
No full textCu2ZnSnS4 (CZTS) quaternary compound has attracted much attention in the last years as new abundant, low cost and non-toxic material, with desirable properties for thin film photovoltaic (PV) applications. In this work, CZTS thin films were grown using two different processes, based on vacuum deposition of precursors, followed by a heat treatment in sulphur atmosphere. The precursors were deposited using two different approaches: (i) electron-beam evaporation of multiple stacks made of ZnS, Sn and Cu and (ii) co-sputtering deposition of the three binary sulphides CuS, SnS and ZnS. All the materials were characterized both as isolated films and as absorber layer in solar cells, produced using the typical structure Mo/CZTS/CdS/i:Zno/AZO.
Both growth processes were found to give good quality kesterite films, showing CZTS as the main phase, large grains and suitable properties for PV application, but higher homogeneity and stoichiometry control were achieved using the co-sputtering route. A detailed investigation on CZTS optical properties, microstructure, intrinsic defect density and their correlation with the material composition is presented. A strong effect of the tin content on the bandgap energy, sub-gap absorption coefficient, crystalline domain and grain size is shown and a model based on the increase of the intrinsic defect density induced by a reduced tin content is proposed. These studies suggested a correlation between the increase of the bandgap energy and the improvement of the material quality, which was also confirmed by the performances of the final devices.
CZTS thin films were then assembled into the solar cells and their properties as absorber layer were optimized by varying both composition and thickness. CZTS samples produced from stacked evaporated precursors allowed achieving a maximum efficiency of 3.2%, but reproducibility limits of the evaporation process made difficult to obtain further and rapid efficiency improvements.
The co-sputtering route was demonstrated to be a more successful strategy, assuring a fine-control of the film composition with good process reproducibility. A fast improvement of solar cell efficiency was obtained using this approach and a maximum efficiency of 5.7% was achieved. The relationship between the absorber layer stoichiometry and the device performances was investigated: the effect of the Zn enrichment and a possible influence of the Cu/Sn ratio on the device performances are discussed. Investigation on CZTS/CdS and CZTS/MoS2 interfaces revealed that the optimization of both buffer-layer and back-contact technology is a primary need for further improvement of CZTS solar cells
Input identification, footbridge control and non-linear identification of a MR damper
No full textThe thesis aims to investigate the dynamical criticality of a pedestrian footbridge and the use of a semi-active tuned mass damper. In this respect, the work appears
threefold since the first and third part regard identification of a realistic model for the
damping device and semi-active control of the magneto-rheological damper. In this
respect, input identification techniques are a useful tool and an aid for the control
law design. As a consequence, the second part involves both input identification
strategies for a dynamic system and analysis of issues related to the inherent delay.
In this respect, the so called “collocation” of measurement devices with respect to
the application points of the input is critical, together with the concept of kernel
Shape-to-color associations in non-synesthetes: perceptual, emotional, and cognitive aspects
No full textThe study of cross-modal and cross-dimensional associations in non-synesthetes has become an increasingly hot topic in recent times (see Spence, 2011, for a review). Despite the many examples of associations between shape/color-stimuli on one hand and stimuli of different sensory nature on the other hand, little is known about the way shape and color are interrelated with each other. The purpose of our research was to test whether non-synesthetes also exhibit systematic associations between these two different dimensions of the visual domain, that is, shape and color. Furthermore, our study also relates to art, and in particular to Kandinsky’s theory on shape-color correspondences (1912, 1926), which could be tested indirectly. The project consisted of six experiments, some of them (Experiments 1-3 and 6) carried out in the Experimental Psychology Labs at the University of Trento under the supervision of Prof. Liliana Albertazzi, and the others (Experiments 4-5) carried out in the Visual Perception and Aesthetics Lab at the University of California Berkeley, under the supervision of Prof. Stephen E. Palmer. Experiment 1 provided the first evidence that people tend to match certain hues to certain simple geometric shapes. The strongest relations were found between the triangle and yellows, and the circle and square with reds, confirming only in part Kandinsky’s artistic findings. Experiment 2 replicated the results of Experiment 1 with a different group of participants and showed that the pattern of shape-color associations that previously emerged was independent of a shape’s size, area/perimeter, and stability. Experiment 3 examined the relation between parts of shapes (angles) and hues, also in order to assess if the choice of a hue to be matched with a given shape could be partly driven by its angles. In the remaining experiments (4-5), we extended the previous studies to color dimensions other than the hue, and to an even wider variety of shapes and shape-features. The shape-features studied included pointedness, intersections, symmetry-axes, concavities, and the number of generating-points. We found that specific shape-features of line-shapes (Experiment 4) or closed geometric shapes (Experiment 5) influence specific color attributes (saturation, lightness, redness/greenness, and yellowness/blueness) of the associated colors. Our results also suggested that shape-color associations may be mediated, in part, by emotions; indeed people tend to match colors and shapes that have similar emotional associations (e.g., angry colors are matched to angry shapes). Finally, Experiment 6 assessed in an exploratory way the association between words related to abstract concepts and hues. Altogether, additional examples of associations in the non-synesthetic population were reported. We suggest that this new trend of research, at large, could improve the study of human perception and cognition, guide the search for neural correlates, as well as find possible applications in a variety of disciplines, including ergonomics, art, and design
Waterborne Paint System Based on CeO2 and Polyaniline Nanoparticles for Anticorrosion Protection of Steel
No full textThis thesis reports the research activity carried out over the last 3 years in the Laboratory of Industrial Corrosion Control at the University of Trento. The subject is related to corrosion control through an organic coating paint system for steel substrates. In other words, it coveres the investigation of anticorrosive pigments as viable alternatives to replace the use of hazardous and toxic substances commonly present into an organic coating paint system and in addition to this, to reduce emissions of volatile organic compounds (VOC), the organic coating paint system itself has been designed to be solvent-free.
Much of the work over the development of a water based full paint system containing the environmentally friendly nanoparticles was based on electrochemical techniques. Therefore, the contents within the next pages are divided into three main parts: i) a background about the use of electrochemical techniques for corrosion and corrosion control through organic coatings; ii) the electrochemical investigations of the environmentally friendly anticorrosive pigments; iii) the incorporation into one water based organic coating system.
Also, great effort has been spent to understand the mechanisms of the coatings degradation as well as the mechanisms of anticorrosion protection given by the pigments. In this way, the results of interest have been delivered to scientific community via a number of publications in different journals as well as congresses participations.
Lastly, the activities in this thesis were supported by the SteelCoat project. SteelCoat was a consortium cooperation project within the EU Seventh Frame Programme (FP7), involving several companies and universities