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Visual stability: perception of stable objects across saccadic eye movements
No full textThe ability of moving freely in the environment gives us the great advantage to directly interact with it, improving our discriminative abilities. For example, if we were to inspect an object without the chance to actively moving around it, then we could only rely on the information that we can extract from a single point of view with respect of the object. We would have restricted access to the object properties and we would then establish our decisions within those limits. Moving actively allow us to overcome these limitations and gain access to a more complete set of informations regarding the object. This would help us decide what to do next, whether or not to interact with an external object and, in case, providing hints on how to interact. To this extent moving and exploring the environment augment our discrimination abilities. Moreover, active movements help us to form a complete sense of space
Analisi sperimentali e numeriche del comportamento di interfaccia tra FRP e calcestruzzo
No full textLo scopo di questo lavoro è stato di sviluppare un programma ad elementi finiti tridimensionale, scritto in Fortran 90, in grado di rappresentare il comportamento di interfaccia di travi in calcestruzzo rinforzate da fogli di FRP, sia in fase elastica, che durante il fenomeno di delaminazione utilizzando la teoria del danno.
Si è inoltre indagato sul comportamento del collegamento FRP-cls a causa di carichi a lunga durata, mediante una sperimentazione e attraverso simulazioni numeriche.
Il modello FEM si basa sulla teoria del contatto [1] legata al danneggiamento per poter simulare tutto il processo di delaminazione partendo dall’innesco dovuto al superamento del limite di resistenza del collegamento, fino al distacco completo del rinforzo.
La modellazione tridimensionale ha consentito ancora, di poter ottenere lo stato tensionale su tutta l’interfaccia, riuscendo quindi a rappresentare il comportamento “di bordo” bidimensionale delle tensioni di taglio riscontrato da numerosi autori in fase di sperimentazione[2],[3], nonché gli effetti di peeling.
I test a lungo termine atti a caratterizzare i parametri viscosi dei materiali, sono stati effettuati attraverso prove a trazioni dei materiali costituenti le matrici polimeriche dell’FRP (resine epossidiche), e attraverso prove su travetti rinforzati da fogli di fibre in carbonio monodirezionali, soggetti a carichi concentrati.
Numericamente i fenomeni differiti sono stati studiati implementando materiali di tipo elastoviscosi sia per il calcestruzzo, utilizzando il modello B3 proposto da Z. Bazant [4], che per l’FRP impiegando un modello micromeccanico proposto in [5].
BIBLIOGRAFIA
[1] P. Wrigger, (2002), “Computational Contact Mechanics”, Springer.
[2] C. Pellegrino, D. Tinazzi, C. Modena, (2008), “Experimental study on Bond Behavior between Concrete and FRP reinforcement”, J. Compos. for Constr.,vol 12(2), 180-189.
[3] K. V. Subramaiam, C. Carloni, L. Nobile, (2007), “Width effect in the interface fracture during shear debonding of FRP sheets from concrete”, Eng. Frac. Mech., vol. 74, 578-594.
[4] Z. Bazant and S. Baweja, Creep and shrinkage prediction model for analysis and design of concrete structures: Model B3, in Adam Neville Symposium: Creep and Shrinkage – Structural Design Effects, ACI SP-194, A. Al-Manaseer Ed., Am. Concrete Institute, Farmington Hills, Michigan, 1–83, 2000.
[5] L. Ascione, V.P. Berardi, G. Mancusi, (2003), “Il Comportamento a lungo termine sotto carichi statici di travi in c.a. placcate con lamine di FRP”, XXXII Congresso AIAS, Salerno.
[6] S. T. Smith, J. G. Teng, (2001), “Interfacial stress in plated beams”, Eng. Struc., vol. 23, 857-871
Simulation and Modeling of the Powder Diffraction Pattern from Nanoparticles: Studying the Effects of Faulting in Small Crystallites
No full textAccurate statistical characterization of nanomaterials is crucial for their use in emerging technologies. This work investigates how different structural characteristics of metal nanoparticles influence the line profiles of the corresponding powder diffraction pattern. The effects of crystallite size, shape, lattice dynamics, and faulting are all systematically studied in terms of their impact on the line profiles.
The studied patterns are simulated from atomistic models of nanoparticles via the Debye function. This approach allows for the existing theories of diffraction to be tested, and extended, in an effort to improve the characterization of small crystallites. It also begins to allow for the incorporation of atomistic simulations into the field of diffraction. Molecular dynamics simulations are shown to be effective in generating realistic structural models and dynamics of an atomic system, and are then used to study the observed features in the powder diffraction pattern.
Furthermore, the characterization of a sample of shape controlled Pt nanoparticles is carried out through the use of a developed Debye function analysis routine in an effort to determine the predominant particle shape. The results of this modeling are shown to be in good agreement with complementary characterization methods, like transmission electron microscopy and cyclic voltammetry
Semi-classical aspect of black hole physics
No full textSemi-classical aspects of black hole physics are studied with particular emphasis on Hawking radiation and its derivation from tunnelling method techniques
Effect of surface treatments on mechanical properties of low alloy sintered steels
No full textPowder Metallurgy (PM) is a net- shape and cost effective technology used for the production of steel parts having good mechanical properties and geometrical precision. In the conventional press and sinter process, the voids among the powder particles cannot be completely eliminated, and the as sintered microstructure contains a certain amount of residual porosity. Mechanical properties are consequently lower than those of the corresponding wrought steels [1]. In particular, the fatigue resistance is significantly affected by porosity; crack tends to nucleate in correspondence of clusters of pores, and to propagate along
the network of interconnected pores [2, 3]. Fatigue resistance can be improved on increasing the density, reducing pore size and pore clustering and enlarging the sintered ligaments between pore, or, similarly to wrought steels, by thermochemical (carburizing and nitriding) or
mechanical treatments (shot peening).
Carburizing consists in a surface carbon enrichment, which gradually decreases towards the core. After quenching high carbon martensite is formed at the surface, characterized by high hardness and a compressive residual stresses suitable for wear and fatigue resistance. Low pressure carburizing is a variant of the conventional gas carburizing performed under sub-atmospheric pressure with
pressurized gas quenching. It is quite attractive for carburized PM sintered steels, for two main reasons.
1. Porosity increases the surface exchange area, enhancing the risk of oxidation mainly in Cr and Cr-Mn steels. Low pressure carburizing uses propane or acetylene, as carburizing gas, which does not contain oxidizing agents.
2. Quenching oil remains entrapped in the open porosity, and has to be eliminated. The possibility to combine low pressure carburizing with gas quenching results in clean parts as well as lower distortion.
However, the combination between the very high carburizing potential of LPC and the large surface area of porous steels results in overcarburizing, with the precipitation of grain boundary carbides in Cr steels, and the formation of retained austenite in the case in Cr free ones [4, 5]. This problem can be solved by either increasing density, to close the residual porosity, or rolling and shot peening, to
eliminate the surface porosity.
Nitriding is based on the nitrogen enrichment of the surface layers of steel. On the base of nitrogen content the surface microstructure can be divided in two zones:
the compound and the diffusion layer. The former is in principle a ceramic layer, whilst the latter consists in the base matrix hardened by solid solution and by the
precipitation of nitrides. The nitride precipitation induces a compressive residual stress field which offers a resistance to the nucleation and propagation of the fatigue crack, improving the fatigue resistance. In order to obtain a hardened and deep diffusion layer the steel has to contain alloying elements with a high affinity for nitrogen, as chromium and molybdenum. Nickel and manganese have a negligible interaction with nitrogen. Among the different nitriding processes, plasma nitriding is recommended for sintered steel. Plasma nitriding is less sensitive to porosity than gas nitriding due to the particular mechanism of nitrogen diffusion (volume diffusion) which allows a uniform diffusion front on the steel surface and a homogeneous nitrogen distribution [6, 7]. Therefore, a preliminary surface densification is not necessary.
Shot peening is a flexible and cost effective solution to improve the fatigue performances of mechanical parts, as gears and springs, thanks to the compressive residual stress generated below the surface and the surface work
hardening. The improvement in fatigue resistance is more effective if shot peening is applied on case hardened steels, because of the more stability of the compressive residual stresses. Since the fatigue strength of sintered steels strongly depends on the material density, shot peening is a useful technique to improve such property, owing to the densification of the surface layer [8, 9]. The
fatigue cracks nucleates beneath this layer and since it cannot propagate in a compression field, it moves towards the core.
This PhD thesis is part of the an international research project, “Höganäs Chair project- fourth round”, financed by Höganäs AB, world leader in the production of ferrous powders, involving four research institutions: Trento University, Technique University of Wien, Carlos III University of Madrid and Slovak Academy of Science,
Institute for Materials Research, Kosice. The aim of the project is to carry out a cooperative study to design highly performing structural steels by the conventional
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Le architetture ecclesiali nei siti d'altura alpini
No full textLa ricerca punta a definire una metodologia operativa ad ampia scala territoriale che possa catalogare, studiare e valutare lo stato di conservazione dei manufatti architettonici emergenti caratterizzanti il territorio trentino d’altura. La conoscenza e lo studio dell’ingente patrimonio architettonico del passato, soprattutto quello ecclesiastico, è finalizzato alla concreta definizione di modus operandi specifici per il recupero di materiali e tecnologie costruttive in architetture che presentano una notevole stratificazione storica artistica – materica – statica, onde evitare le omogeneizzazioni e le semplificazioni negli interventi di recupero che si sono verificati negli ultimi decenni, per la mancanza di conoscenze approfondite soprattutto in particolari ambiti montani.
Lo studio è strettamente connesso ad uno dei grandi progetti 2006 della Provincia Autonoma di Trento, il progetto APSAT (Ambiente e Paesaggio dei Siti Altura Trentini), finalizzato alla rivalutazione dei siti d’altura alpini mediante l’analisi e la comprensione dei complessi sistemi antropici che si sono sviluppati e stratificati nel tempo fino ad arrivare all’attuale assetto socio - economico e culturale - territoriale.
E' stato necessario assumere un’area campione, la Val di Gresta (Vallagarina), che per le sue contenute dimensioni geografiche ben si presta ad una lettura approfondita e multiscala.
Lo studio, articolato su più livelli e su più ambiti di ricerca, ha individuato le relazioni tra manufatti e ambiente naturale, tra diversi tipi edilizi nel loro rapporto con le infrastrutture e il paesaggio, determinando input di trasformazione comuni a tutti i sistemi antropici
Da ribelli a resilienti: processi generativi di successo scolastico nel biennio della scuola secondaria in Italia
No full textL’istruzione e la formazione hanno acquisito un peso progressivamente crescente nell’agenda politica dell’Unione Europea.
Chi possiede competenze di basso livello rischia l’esclusione economica e sociale (Consiglio dell’Unione europea, 2008, p.2).
In una ricerca su alcune dimensioni della disuguaglianza in Italia (povertà, salute, condizioni abitative) condotta nell’ambito dell’Osservatorio sulle disuguaglianze sociali della Fondazione Ermanno Gorrieri, si rileva come, nell’anno 2006, la maggiore quota percentuale tra le persone a basso reddito fosse costituita in Italia dagli operai (37,6%), seguiti dai pensionati (29,6%) (Brandolini, Saraceno, Schizzerotto, 2009, p.52).
In Italia, il tasso medio di abbandono scolastico misurato con l’ultimo test Pisa nel 2009 è del 23,5%, percentuale che esclude gli studenti dei Centri di formazione professionale, essendo questi ultimi disciplinati dalla normativa regionale e pertanto fonte di dati difficilmente comparabili. Questo significa che, mediamente, almeno uno/a studente/ssa italiano/a su quattro è “a rischio di esclusione economica e sociale”. Aggiungendo a questo dato i tassi di dispersione scolastica e di evasione e i risultati circa le competenze di base in uscita al termine del ciclo d’istruzione secondaria (Ministero dell’Istruzione, Università e Ricerca, 2008b), è legittimo pensare che questo problema interessi una fetta ben maggiore di studenti italiani.
Questo studio si propone di indagare cosa accade prima dell’abbandono, quando gli studenti sono ancora all’interno del circuito formativo obbligatorio: quali processi interni alla scuola secondaria conducono verso il successo o l’insuccesso scolastico? Quali fattori entrano in gioco, ai diversi livelli?
Per fare questo, è stato necessario in primo luogo decostruire e problematizzare la definizione di “insuccesso scolastico”, facendo una comparazione tra le mutevoli descrizioni concettuali che ne sono state date e compiendo una disanima critica delle modalità utilizzate per quantificare il fenomeno, prendendo in esame alcune indagini italiane ed internazionali.
Attraverso un breve excursus storico sull’evoluzione del sistema scolastico in Italia e sui riferimenti normativi che lo disciplinano, sia a livello nazionale, sia a livello europeo, si è in seguito fornita una descrizione quantitativa del fenomeno “insuccesso scolastico” in Italia, seguita da una lettura critica dei diversi approcci disciplinari che hanno fatto dell’insuccesso scolastico il loro oggetto d’indagine, in Italia e all’estero.
Tra i vari approcci presentati, ci si è focalizzati in particolar modo su quello della sociologia dell’educazione e della critical pedagogy nella sua accezione statunitense: quest’ultimo viene proposto con l’approccio più fecondo nello studio del fenomeno, proponendone un confronto con l’approccio della pedagogia critica italiana.
Questo studio si colloca tra le ricerche empiriche che si rifanno all’approccio della critical pedagogy.
La metodologia utilizzata è una grounded theory orientata alla social justice, combinata con un approccio etnografico.
Lo studio si conclude con la presentazione di un modello teorico che si propone di spiegare il fenomeno “insuccesso scolastico” nelle sue origini, e di fornire utili indicazioni agli operatori sul campo che quotidianamente si misurano con il fenomeno stesso
Intrinsic Lipschitz graphs in Heisenberg groups and non linear sub-elliptic PDEs
No full textIn this thesis we study intrinsic Lipschitz functions. In particular we provide a regular approximation result and a Poincarè type inequality for this class of functions. Moreover we study the obstacle problem in the Heisenberg group and we prove a geometric Poincarè inequality for a class of semilinear equations in the Engel group
Collecting Common Sense from text and People
No full textIn order to display human-like intelligence, advanced computational systems should have access to the vast network of generic facts about the world that humans possess and that is known as commonsense knowledge (books have pages, grocery has a price, ...). Developers of AI applications have long been aware of this, and, for decades, they have invested in the laborious and expensive manual creation of commonsense knowledge repositories. An automated, high-throughput and low-noise method for commonsense collection still remains as the holy grail of AI.
Two relatively recent developments in computer science and computational linguistics that may provide an answer to the commonsense collection problem are text mining from large amounts of data, something that has become possible with the massive availability of text on the Web, and human computation, which is a workaround technique implemented by outsourcing the 'hard' sub-steps of a problem to people. Text mining has been very successful in extracting huge amounts of commonsense knowledge from data, but the extracted knowledge tends to be extremely noisy. Human computation is also a challenging problem because people can provide unreliable data and may lack motivation to solve problems on behalf of researchers and engineers. A clever, and recently popularized, technique to motivate people to contribute to such projects it to pose the problems as entertaining games and let people solve those problems while they play a game. This technique, commonly known as games-with-a-purpose approach, has proved a very powerful way of recruiting laypeople on the Web.
The focus of this thesis is to study methods to collect common sense from people via human computation and from text via text mining, and explore the opportunities in bringing these two types of methods together. The first contribution of my study is the introduction of a novel text miner trained on a set of known commonsense facts. The text miner is called BagPack and it is based on a vector-space representation of concept pairs, that also captures the relation between the pairs. BagPack harvests a large number of facts from Web-based corpora and these facts constitute a -- possibly noisy -- set of candidate facts.
The second contribution of the thesis is Concept Game, a game with a purpose which is a simple slot-machine game that presents the candidate facts -- that are mined by BagPack -- to the players. Players are asked to recognize the meaningful facts and discard the meaningless facts in order to score points. Thus, as a result, laypeople verify the candidate set and we obtain a refined, high-quality dataset of commonsense facts.
The evaluation of both systems suggests that text mining and human computation can work very efficiently in tandem. BagPack acts as an almost-endless source of candidate facts which are likely to be true, and Concept Game taps laypeople to verify these candidates. Using Web-based text as a source of commonsense knowledge has several advantages with respect to a purely human-computation system which relies on people as the source of information. Most importantly, we can tap domains that people do not talk about when they are directly asked. Also, relying on people just as a source of verification makes it possible to design fast-paced games with a low cognitive burden.
The third issue that I addressed in this thesis is the subjective and stereotypical knowledge which constitutes an important part of our commonsense repository. Regardless of whether one would like to keep such knowledge in an AI system, being able to identify the subjectivity and detect the stereotypical knowledge is an important problem. As a case study, I focused on stereotypical gender expectations about actions. For this purpose, I created a gold standard of actions (e.g., pay bill, become nurse) rated by human judges on whether they are masculine or feminine actions. After that, I extracted, combined, and evaluated two different types of data to predict the gold standard. The first type of data depends on the metadata provided by social media (in particular, the genders of users in a microblogging site like Twitter) and the second one depends on Web-corpus-based pronoun/name gender heuristics. The metadata about the Twitter users helps us to identify which actions are mentioned more frequently by which gender. The Web-corpus-based score helps us to identify which gender is more frequently reported to be carrying out a given action. The evaluation of both methods suggests that 1) it is possible to predict the human gold standard with considerable success, 2) the two methods capture different aspects of stereotypical knowledge, and 3) they work best when combined together
