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Computational problems in algebra: units in group rings and subalgebras of real simple Lie algebras
No full textIn the first part of the thesis I produce and implement an algorithm for obtaining generators of the unit group of the integral group ring ZG of finite abelian group G. We use our implementation in MAGMA of this algorithm to compute the unit group of ZG for G of order up to 110. In the second part of the thesis I show how to construct multiplication tables of the semisimple real Lie algebras. Next I give an algorithm, based on the work of Sugiura, to find all Cartan subalgebra of such a Lie algebra. Finally I show algorithms for finding semisimple subalgebras of a given semisimple real Lie algebra
Data fusion of images and 3D range data
No full textA robot is a machine that embodies decades of research and development. Born as a simple mechanical devices, these machines evolved together with our technology and knowledge, reaching levels of automation never imagined before. The modern dream is represented by the cooperative robotics, where the robots do not just work for the people, but together with the people. Such result can be achieved only if these machines are able to acquire knowledge through perception, in other words they need to collect sensor measurements from which they extract meaningful information of the environment in order to adapt their behavior. This thesis speaks about the topic of the autonomous object recognition and picking for Automated Guided Vehicles, AGVs, robots employed nowadays in the automatic logistic plants. The development of a technology capable of achieving such task would be a significant technological improvement compared to the structure currently used in this field: rigid, strongly constrained and with a very limited human machine interaction. Automating the process of picking by making such vehicles more smart would open to many possibilities, both in terms of organization of the plants, both for the remarkable economic implications deriving from the abatement of many of the associated fixed costs. The logistics field is indeed a niche, in which the costs of the technology represent the true limit to its spread, costs due mainly to the limitations of the current technology. The work is therefore aimed at creating a stand-alone technology, usable directly on board of the modern AGVs, with minimal modifications in terms of hardware and software.
The elements that made possible such development are the multi-sensor approach and data-fusion. The thesis starts with the analysis of the state of the art related of the field of the automated logistic, focusing mostly on the most innovative applications and researches on the automatization of the load/unload of the goods in the modern logistic plants. What emerges form the analysis it is that there is a technological gap between the world of the research and the industrial reality: the results and solutions proposed by the first seem not match the requirements and specification of the second.
The second part of the thesis is dedicated to the sensors used: industrial cameras, planar 2D safety laser scanners and 3D time of flight cameras (TOF). For every device a specific (and independent) process is developed in order to recognize and localize Euro pallets: the information that AGVs require in order to perform the picking of an object are the three coordinates that define its pose in the 2D space, , position and attitude. The focus is addressed both on the maximization of the reliability of the algorithms and both on the capability in providing a correct estimation of uncertainty of the results. The information content that comes from the uncertainty represents a key aspect for this work, in which the probabilistic characterization of the results and the adoption of the guidelines of the measurement field are the basis for a new approach to the problem. That allowed both the modification of state of the art algorithms both the development of new ones, developing a system that in the final implementation and tests has shown a reliability in the identification process sufficiently high to fulfill the industrial standards, 99\% of positive identifications.
The third part is devoted to the calibration of system. In order to ensure a reliable process of identification and picking it is indeed fundamental to evaluate the relations between the sensing devices, sensor-sensor calibration, but also to relate the results obtained with the machine, sensor-robot calibration. These calibrations are critical steps that characterize the measurement chain between the target object and the robot controller. From that chain depends the overall accuracy in performing the forking procedure and, more important, the safety of such operation.
The fourth part represents the core element of the thesis, the fusion of the identifications obtained from the different sensors. The multi-sensor approach is a strategy that allows the overcome of possible operational limits due to the measurement capabilities of the individual sensors, taking the best from the different devices and thus improving the performance of the entire system. This is particularly true in the case in which there are independent information sources, these, once fused, provide results way more reliable than the simple comparison of the data. Because of the different typology of the sensors involved, Cartesian ones like the laser and the TOF, and perspective ones like the camera, a specific fusion strategy is developed. The main benefit that the fusion provides is a reliable rejection of the possible false positives, which could cause very dangerous situations like the impact with objects or worst. A further contribution of this thesis is the risk prediction for the maneuver of picking. Knowing the uncertainty in the identification process, in calibration and in the motion of the vehicle it is possible to evaluate the confidence interval associated to a safe forking, the one that occurs without impact between the tines and the pallet. That is critical for the decision making logic of the AGV in order to ensure a safe functionality of the machine during all daily operations.
Last part of the thesis presents the experimental results. The aforementioned topics have been implemented on a real robot, testing the behavior of the developed algorithms in various operative conditions
Engineered Alumina / Silicon Carbide Laminated Composites
No full textHigh-melting temperature oxides, carbides and nitrides are superior in hardness and strength to metals, especially in severe conditions. However, the extensive use of such ceramics in structural engineering applications often encountered critical problems due to their lack of damage tolerance and to the limited mechanical reliability. Several ceramic composites and, in particular, laminated structures have been developed in recent years to enhance strength, toughness and to improve flaw tolerance. Significant strength increase and improved mechanical reliability, in terms of Weibull modulus or minimum threshold failure stress, can be achieved by the engineering of the critical surface region in the ceramic component. Such effect can be realized by using a laminated composite structure with tailored sub-surface insertion of layers with different composition. Such laminate is able to develop, upon co-sintering, a spatial variation of residual stress with maximum compression at specific depth from the surface due to the differences in thermal expansion coefficient of the constituting layers.
In the present work silicon carbide has been selected as second phase to graduate the thermal expansion coefficient of alumina due to its relatively low specific density that could allow the production of lighter components with improved mechanical performance, also for high temperature applications. Ceramic laminates with strong interfaces composed of Al2O3/SiC composite layers were produced by pressureless sintering or Spark Plasma Sintering (SPS) of green layers stacks prepared by tape casting water-based suspensions. Monolithic composites containing up to 30 vol% silicon carbide were fabricated and thoroughly characterized. Five engineered ceramic laminates with peculiar layers combination that is able to promote the stable growth of surface defects before final failure were also designed and produced. By changing the composition of the stacked laminae and the architecture of the laminate, tailored residual stress profile and T-curve were generated after co-sintering and successive cooling in each multilayer.
The results of the mechanical characterization show that the engineered laminates are sensibly stronger than parent monolithic composite ceramic and exhibit surface damage insensitivity, according to the design. Such shielding effect is especially observed when macroscopic cracks are introduced by high load Vickers indentations. Some designed multilayers exhibit reduced strength scatter and higher Weibull modulus, which implies superior mechanical reliability. Fractographic observations on fracture surfaces of the engineered laminates show a graceful crack propagation within the surface layers in residual compressive stress which can be attributed to the stable growth of superficial cracks before final failure as it is predicted by the apparent fracture toughness curve. Such fracture behaviour is considered to be responsible for the peculiar surface damage insensitivity and the improved mechanical performance
Innovation, Management and Public Policies: Three Essays on Firm Productivity and Efficiency Analysis
No full textProductivity, i.e., the efficiency with which nations, industries and firms use resources to achieve economically valuable results, is perhaps the most important measure available to policy-makers to gauge the health of an economic system. Early empirical explorations based on country- or industry-level data relied on representative firm paradigms. However, the increasing availability of firm-level data has provided robust evidence for the existence and persistence of wide productivity differentials among firms. In particular, questions regarding what supports such wide heterogeneity, which factors matter most, whether factors influencing productivity can be controlled by firms or are purely external products of the operating environment and which policies can be used to boost productivity growth are all of primary importance. This thesis contributes to the empirical literature on firm productivity with three core papers. The first re-examines the slowdown in productivity in Italian manufacturing by studying the link between innovation, imitation and human capital, which sustained wide heterogeneity of firm productivity behind the aggregate flat productivity trend. The second paper extends analysis to the services sector, in particular to tourism. At a very disaggregated level, it identifies the various sources of differences in productive efficiency of hotels stemming from entrepreneurial and managerial factors, and external to firm factors. The third paper examines the effect of public policy in tourism. A methodological advance is proposed by defining an econometric framework, which allows us to identify and estimate not only the direct but also the indirect effects which public policies may have on hotel performance, in a dynamic treatment setting
Sintering of Ceramic Materials Under Electric Field
No full textThe remarkable discovery of flash sintering came across during the early work of Cologna et al. and emerged as an attractive technique in the field of ceramic processing. In this technique the applied electric field initiates the “flash” event, while the densification is controlled by the current density set. Sintering occurs in less than 5 s at a threshold temperature for a given applied field.
The objective of this thesis is to analyse the phenomena of flash sintering with different ceramic oxides; such as alumina-zirconia composite, hydroxyapatite and doped-alumina. The technique involved the application of constant electric field to a dog bone shaped specimen by means of two platinum electrodes while heating. Experiments were performed either in constant heating rate or in Isothermal condition. For the two-phase 3YSZ-alumina ceramic flash sintering was studied by constant heating rate (CHR) and isothermal sintering experiments. In CHR experiment the 50 vol% 3YSZ-alumina composite was shown to flash sinter at a furnace temperature of 1060°C under an electrical field of 150 V cm−1. Conversely, undoped single-phase alumina remains immune to sintering under fields up to 1000 V cm−1, although single-phase 3YSZ flash sinters at 750°C (furnace temperature). The mechanisms of field assisted sintering are divided into two regimes. At low fields the sintering rate increases gradually (FAST), while at high fields sintering occurs abruptly (FLASH). Interestingly, alumina/zirconia composites show a hybrid behaviour such that early sintering occurs in FAST mode, which is then followed by flash-sintering. The specimens held in the flashed state, after they had sintered to nearly full density, show much higher rate of grain growth than in conventional experiments. These results are in contrast to earlier work where the rate of grain growth had been shown to be slower under weak electrical fields.
In the case of isothermal field-assisted sintering of two-phase, 50 vol% 3YSZ-alumina, the composites exhibit an incubation time for the onset of the flash event. Weaker applied fields and lower temperatures lengthen the incubation period. The effect is highly non-linear. For example at 1300°C and 150 V cm–1 the flash occurs nearly instanteously (in 10 s), but extends to two hours at 1275°C and 65 V cm–1. This behaviour is reminiscent of nucleation and growth phenomena in chemically driven experiments involving phase transformations in the solid state. Here, a model for nucleation under electrical driving forces, based upon the growth of embryos of colossal permittivity is presented. The flash sintering was also studied for composites with in-creasing volume faction of alumina in zirconia (10-50 vol%). The flash onset temperature or the incubation time for the 3YSZ-alumina composites increases with increasing the alumina volume fraction.
In case of CHR experiments of hydroxyapatite, flash effect was shown at 840°C for an applied field of 2000 V cm-1. All the flash sintered samples show stable hydroxyapatite phase. However the sample sintered at 500 V cm-1 requires higher sintering temperature and shows enhanced preferred orientation due to higher diffusivity along c-axis.
In case of alumina, field in excess to 1000 V cm-1 are re-quired to induce flash effect, whereas doped alumina shows flash sintering at 1000 V cm-1
Towards Energy Efficient Cooperative Spectrum Sensing in Cognitive Radio Networks
No full textCognitive radio has been proposed as a promising technology to resolve the spectrum scarcity problem by dynamically exploiting underutilized spectrum bands. Cognitive radio technology allows unlicensed users, also called cognitive users (CUs), to exploit the spectrum vacancies at any time with no or limited extra interference at the licensed users. Usually, cognitive radios create networks in order to better identify spectrum vacancies, avoid resultant interference, and consequently, magnify their revenues. One of the main challenges in cognitive radio networks is the high energy consumption, which may limit their implementation especially in battery-powered terminals.
The initial step in cognitive transmission is called spectrum sensing. In spectrum sensing, a CU senses the spectrum in order to detect the activity of the licensed
users. Spectrum sensing is usually accomplished cooperatively in order to improve the reliability of its results. In cooperative spectrum sensing (CSS), individual sensing results should be exchanged in order to make a global decision regarding spectrum occupancy. Thus, CSS consumes a significant a mount of energy, representing a challenge for CUs. Moreover, the periodicity of CSS and increasing the number of channels to be sensed complicates the problem. To this end, energy efficiency in CSS has gained an increasing attention recently.
In this dissertation, a number of energy-efficient algorithms/schemes for CSS is proposed. The proposed works include energy efficient solutions for low energy consumption in local sensing stage, results’ reporting stage and decision-making stage. The proposed works are evaluated in terms of the achievable energy efficiency and detection accuracy, where they show a significant improvement compared to the state-of-the-art proposals. Moreover, a comprehensive energy-efficient approaches are proposed by combining different algorithms presented in this dissertation. These comprehensive approaches aim at proving the consistency of the proposed algorithms to each other and maximizing the achievable energy efficiency in the whole CSS process. Moreover, high energy consumption is not the only challenge of CSS. Another important problem in CSS is the vulnerability of the security risks which can effectively degrade the energy efficiency of cognitive radio networks. In this dissertation, we propose three different strategies against security attackers. Specifically, authentication protocol for outsider attackers, elimination algorithm for insider attackers, and a punishment policy are presented in this dissertation. While designing these strategies, an eye is kept on energy efficiency such that increasing immunity against attacker does not affect energy efficiency. Therefore, the tradeoff between energy efficiency and security in CSS has been achieved
«Sens e Razos d'una Escriptura»: edizione e studio della traduzione Occitana dell'Evangelium Nicodemi = «Sens e Razos d'una Escriptura»: édition et étude de la traduction Occitane de l'Evangelium Nicodemi
No full textLa tesi fornisce la prima edizione critica commentata del poema occitano 'Sens e razos d'una escriptura', il cosiddetto Vangelo occitano di Nicodemo. Si tratta di un testo in couplets d'octosyllabes, di origine linguadociana orientale e attribuibile, verosimilmente, agli anni '80/'90 del XIII secolo. Un'ampia introduzione di carattere storico-letterario, filologico e codicologico anticipa l'edizione stessa (corredata da traduzione in italiano) e fornisce un primo tentativo di contestualizzazione del testo
Il ruolo della deontologia medica nel sistema delle fonti del diritto: un'analisi comparata. Le rôle de la déontologie médicale dans les sources du droit :analyse comparée.
No full textL’obiettivo della presente tesi è un’analisi comparata del ruolo della deontologia medica nel sistema delle fonti del diritto in Italia, Francia e Germania. Nella prima Parte alcune considerazioni preliminari e l’analisi linguistica hanno permesso di definire l’ambito di indagine e i profili di maggiore complessità del rapporto tra dimensione deontologica e dimensione giuridica sui quali nelle Parti successive si è concentrata l’indagine. La seconda Parte, dedicata alla codificazione dell’etica medica, ha messo in luce la varietà di soluzioni e di modalità di ingresso della norma deontologica nell’ordinamento giuridico. Dal punto di vista comparato, possono distinguersi almeno due modelli principali. In alcuni ordinamenti, infatti, il codice deontologico assume la forma di una fonte del diritto e viene collocato così in maniera “non mediata” nel sistema delle fonti dell’ordinamento statale. Nel modello di ingresso “mediato”, invece, la norma deontologica acquisisce rilevanza sul piano giuridico attraverso il rinvio che ad essa fanno altri principi, norme e clausole generali dell’ordinamento. Il codice di deontologia medica italiano rientra in questo secondo modello, poiché, nonostante assuma significativa rilevanza sul piano giuridico, dal punto di vista strettamente formale rimane ancora un regolamento interno alla categoria professionale. Del modello “non mediato” fanno invece parte il codice deontologico francese (e, più in generale, la categoria di déontologies étatiques, a cui esso appartiene) e le Berufsordnungen del Länder tedeschi. Ciò nonostante, le due esperienze presentano diversità sostanziali nella struttura dei rapporti tra diritto e deontologia. Nell’ordinamento francese il codice di deontologia medica diventa infatti una fonte dello Stato poiché viene pubblicato sul Journal Officiel come decreto del Primo Ministro, nello specifico come décret en Conseil d’Etat, ossia un decreto per il quale è obbligatorio il parere del Consiglio di Stato francese ed è stato infine integrato in un codice statale, il Code de la santé publique. In Germania, invece, i codici deontologici vengono emanati dagli ordini professionali con la forma di Satzungen, fonti sublegislative (untergesetzlich) che rimangono però espressione dell’autonomia amministrativa riconosciuta agli ordini professionali in qualità di Körperschaft des öffentlichen Rechts. Rispetto a questi due modelli, in Italia la collocazione del codice deontologico tra le fonti del diritto risulta quindi più complesso e la definizione della sua natura giuridica rimane ancora controversa.
Nella terza Parte è stato analizzato il ruolo della deontologia medica nell’ambito del biodiritto, sottolineando innanzitutto l’esistenza di un nucleo di principi comuni ai codici deontologici, i quali si sono progressivamente aperti ad una sostanziale tutela dei diritti fondamentali della persona assistita, in sintonia con i principi elaborati a livello costituzionale, nazionale e internazionale. L’analisi comparata dei rapporti tra deontologia e diritto in alcuni ambiti specifici ha però evidenziato come, al di là di tale nucleo comune, l’evoluzione di contenuti concreti dei codici e l’ampiezza di determinate discipline dipenda da quattro fattori principali: le caratteristiche dell’oggetto da disciplinare; le scelte di intervento dell’ordinamento giuridico nell’ambito del biodiritto; il modello dei rapporti tra diritto e deontologia medica e la capacità della categoria professionale di farsi carico delle nuove esigenze di tutela dei diritti fondamentali. La combinazione tra questi fattori può variare in maniera significativa nei singoli ordinamenti, dando vita ad esiti anche molto diversi sul piano normativo. Lo studio di alcuni specifici ambiti del biodiritto ha messo inoltre in luce le peculiarità del ruolo della deontologia medica, la quale svolge una funzione essenziale nella definizione del caso concreto, ma può anche costituire fonte di disciplina specifica del biodiritto, in ragione di un’inerzia o di una specifica delega del legislatore. La quarta Parte è dedicata alla violazione della deontologia e ai procedimenti disciplinari, che sono stati valutati in relazione alla loro idoneità ad emancipare l’accertamento della responsabilità deontologica dalla dimensione meramente corporativistica. Infine nella Parte conclusiva sono stati analizzati alcuni profili legati alla dimensione europea della deontologia e, alla luce di quanto emerso dall’analisi comparata, sono state proposte alcune ipotesi di riforma per un modello italiano più coerente, flessibile ed efficace dei rapporti tra diritto e deontologia
Uno studio comparato sulle disuguaglianze di salute: Italia e Francia
No full textThe foundations of this work of research derived by the demonstration that the health is conditioning of a multiplicity by factors, the control of which is not exercised by the only health care system. Health inequalities, representing one of the most unjust and severe inequitable forms because health is one of the pre-conditions in order to live out fully individual life. Health inequality constitutes one of the worst scandals of our time, especially in developed and democratic countries.
The theme of health inequalities is a subject beloved to the sociology, because their analysis allows, either to observe the social dynamics, either to understand as the social differences are distributed between the individuals within the society, especially with the current global economic crisis. The main objective of this study is, using comparative analysis, identify and distinguish the inequalities in health in the relationship between social conditions, risk factors, territorial context and state of health of the population, in two European countries (France and Italy), in order to understand their dynamics and as the territorial context affects the inequalities of health of individuals. Through a transnational approach this research project identifies differences and similarities between the two case studies. The results from our analysis, demonstrate the existence of "unexpected" similarities between groups of French and Italian people, despite different characteristics of social welfare and health systems
Ground state and dynamical properties of many-body systems by non conventional Quantum Monte Carlo algorithms
No full textIn this work we develop Quantum Monte Carlo techniques suitable for exploring both ground state and dynamical properties of interacting many-body systems. We then apply these techniques to the study of excitations in superfluid He4 and to explore the structure of nuclear systems using chiral effective field theory interactions