1731 research outputs found
Sort by
Il passato nel presente. Identità e orientamenti politici nei ragionamenti degli elettori di un comune italiano alla vigilia delle Elezioni Europee del 2014
No full textLa ricerca mira a ricostruire la definizione della situazione politica che alcuni elettori italiani hanno prodotto per maturare la propria scelta di voto in occasione delle Elezioni Europee del 2014. Per poter agire infatti, gli individui hanno prima bisogno di comprendere la situazione nella quale agiscono. I risultati mostrano che, a seguito dei cambiamenti avvenuti nel panorama politico italiano l'anno precedente, elettori, partiti e leader si sono mossi a velocità diverse, faticando nel condividere una medesima definizione. Rilevare questa situazione di disallineamento aiuta a comprendere, in generale, gli effetti della valence politics sul voto e, nello specifico, il percorso politico dei partiti italiani
On some optimal control problems on networks, stratied domains, and controllability of motion in fluids.
No full textThe thesis deals with various problems arising in deterministic control, jumping processes and control for locomotion in fluids. It is divided in three parts.
The first part is focused on some optimal control problems on network and stratified domains with junctions, where each edge/hyper-plane has its own controlled dynamics and cost. We consider some possible approximations for such a problems given by the use of a switching rule of delayed-relay type and study the passage to the limit when the parameter of the approximation goes to zero. First, we take into account some problems on network: a twofold junction problem, a threefold junction one and an extension of the last one. For each of these problems we characterize the limit functions as viscosity solution and maximal subsolution of a suitable Hamilton-Jacobi problem. Secondly, we consider a bi-dimensional multi-domain problem and as done for the problems on network we characterize the limit function as viscosity solution of a suitable Hamilton-Jacobi problem.
The second part studies a decentralized routing problem over a network, using the paradigm of mean-field games with large number of players. Building on a state-space extension technique, we turn the problem into an optimal control one for each single player. The main contribution is an explicit expression of the optimal decentralized control which guarantees the convergence both to local and to global equilibrium points. Furthermore, we study the stability of the system also in the presence of a delay which we model using an hysteresis operator. As a result of the hysteresis, we prove existence of multiple equilibrium points and analyze convergence conditions.
In the last part of the thesis we investigate different
strategies to overcome the so-called scallop paradox concerning periodic locomotion in fluid. We show how to obtain a net motion exploiting the fluid's type change during a periodic deformation. We consider two different models: in the first one that change is linked to the magnitude of the opening and closing velocity of the scallop's valves. Instead, in the second one it is related to the sign of the above velocity. In both cases we prove that the mechanical system is controllable, i.e. the scallop is able to move both forward and backward using cyclical deformations
Aspetti dell'interazione culturale tra Greci e Persiani. Intrecci di culture in contesto conflittuale (546-350 a.C. ca.)
No full textIl lavoro di tesi si propone lo scopo di studiare alcuni aspetti dell’interazione culturale tra Greci e Persiani inscritti in contesti di conflittualità a carattere prevalentemente bellica. Per raggiungere questo obiettivo, si è tentato di rispondere a una serie di domande, interpellando l’evidenza documentaria nella sua molteplicità. In primo luogo, (i) se si potessero rintracciare occasioni effettive di contatto e di scambio culturale tra Greci e Persiani, in seno alla loro secolare situazione conflittuale; in secondo luogo (ii) chi fossero i protagonisti e i vettori degli eventuali fenomeni di trasferimento culturale; (iii) attraverso quali canali e in che contesti essi si verificarono; (iv) in che modo i pattern del contatto culturale cambiarono sulla lunga durata; e infine (v) fino a che punto fosse possibile pensare a Greci e Persiani come a due gruppi appartenenti a sfere culturali sempre e dovunque nettamente distinte.
La tesi si dissocia dalla tradizionale narrativa a sfondo politico-militare, prettamente evenemenziale concepita sostanzialmente come histoire-bataille. Prende inoltre le distanze da quel filone storiografico moderno che ha spesso fedelmente seguito le rappresentazioni dei testi ‘classici’, raccontando solo eventi decisivi, inseriti in un quadro di generale ostilità e contrapposizione tra due blocchi: un “mondo greco” e un “mondo persiano” non comunicanti e monolitici. Essa si propone invece di indagare il conflitto come momento e contesto produttivo di cambiamenti culturali.
Alla luce delle prospettive innovative offerte dagli Achaemenid Studies, degli apporti metodologici della ricerca storico-antropologica sulle interazioni culturali e della sociologia del conflitto, la prospettiva dei culture contacts adottata nel lavoro intende affiancarsi in maniera innovativa ma complementare ai paradigmi interpretativi correnti. Tale approccio multidisciplinare è richiesto dall’argomento stesso della ricerca, che si caratterizza per una netta sproporzione documentaria, che vede i materiali classificabili come achemenidi in chiara minoranza rispetto al resto dell’evidenza. D’altronde, il lavoro di ricerca si interessa al contatto e allo scambio culturale in modo da dare a entrambe le parti un ruolo attivo e decentralizzare così il focus da un modello monolitico di cultura, orientandolo verso l’agency individuale: da qui, anche la scelta della nozione di interazione culturale presente nel titolo.
L’indagine spazia tra due secoli di contatti in Asia Minore, contesto privilegiato per lo studio di fenomeni di interscambio culturale tra Greci e Persiani. Non ambisce alla copertura sistematica dell’evidenza disponibile, ponendosi invece l’obiettivo di selezionare alcuni casi rilevanti e avviare una prima disamina delle situazioni che si prestano maggiormente a un’interpretazione in chiave culturale, lasciando aperta per il futuro la possibilità ad altri studi di migliorare e approfondire quanto rimasto in sospeso
DCT Enabled smart consumer Grid Model
Get PDFSustainable energy and energy harvesting has become a hot research area due to the shortage of fossil energy resources and burning fossil fuels release greenhouse gases in our environment, which is partaking in gradually increasing of surrounding temperature of our environment. Therefore, the penetration of various types of renewable/ distributed sources, onsite storage devices and DC powered appliances has recently focused attention towards DC power distribution in consumer grids to achieve the target of zero/positive energy buildings and communities. As compared to AC micro grid, many recent studies revealed that DC distribution has many advantages over the convectional AC distribution in term of high efficiency, integration of renewable/ distributed sources and storage locally. The objective of this dissertation is to propose reliable, cost-effective, sustainable, scalable DC consumer grid architecture which can integrate not only renewable/ distributed sources and storage, but also fully compatible with the convectional AC distribution network without any significant change or upgrade. In order to achieve this goal, we proposed the DC Transformer (DCT) enabled consumer grid model. The DC Transformer has been regarded as one of the most emerging technologies and it has many advantages over the convectional low frequency AC transformers such as high power density in small area, voltage regulation, reactive power compensation, fault detection and isolation etc. Apart from advantages, DCT required intelligent control algorithm and additional supervisory circuit makes it complicated and expensive. Therefore, in our proposed model we discussed the pros and cons of typical Solid-State transformer topologies already proposed and explained the topology used in the DCT transformer. Furthermore, in state of the art models, authors used three stages of grid operational modes, which is usually based on different factors such as the status of grid connections, State of charge of Battery storage and output power from locally available sources. However, we introduced four stages excluding buffering stage. All stages are depended upon the practical situations consumer grid may face during normal grid operations such as, DCT Isolation mode, if main grid and local generators are not available then how our proposed model would manage the locally available storage. Main grid interactive mode, we discussed the existing or convectional grid operational condition. In case of no local generator available and the AC main is the only source of power. Self-reliance grid operation, when the renewable energy sources are generating enough energy to fulfil demand side power requirements. Moreover, we explain the safest transition technique from grid connected mode to self-reliance mode without effecting overall grid stability and reliability, called buffer state. Power sharing mode, in this mode we discussed how the locally consumer grid would share surplus energy with adjacent consumer grids without effecting or compromising its own stability. The purpose of proposing critical operational modes and defining the rigid criteria between transitions of each mode is to operate whole grid flawlessly in any real time condition. Moreover, we introduced “Buffer stage” in between the grid connected and self-reliance mode to take into account that renewable sources are stochastic in nature and to avoid any grid stability issue. The operational modes are among key techniques of our proposed architecture and the detail contribution of our proposed model is mentioned in section . Some practical issues related to the DC micro grid are also examined in detail, such as overall grid control algorithm, power management strategy, demand side management, fault isolation and rectification are highlighted and the solution of these issues also presented with detail simulation results. Furthermore, the state of art DC grid models are proposed for specific type of renewable source(s) such as PV, wind or combination of both. In our proposed architecture, we are not depending on any specific type of renewable and distributed source or storage. We proposed the standard interfaces for possible type of renewable /distributed sources, storage and grid connection. Therefore, by using the standard interface any type of the source and storage can be plug-n-play in PCmRC model. However, the main objectives are to maximize the exploitation of renewable-sources, to decrease reliance on fossil-fuel, to boost the overall efficiency of the grid by reducing the power-conversion losses and full management of end user demand in all possible forms. The simulation platform is designed in MATLAB/Simulink. Several types of case studies and simulation results show the effectiveness of the proposed power distribution and management model
Black-Box Security Testing of Browser-Based Security Protocols
No full textMillions of computer users worldwide use the Internet every day for consuming web-based services (e.g., for purchasing products from online stores, for storing sensitive files in cloud-based file storage web sites, etc.). Browser-based security protocols (i.e. security protocols that run over the Hypertext Transfer Protocol and are executable by commercial web-browsers) are used to ensure the security of these services. Multiple parties are often involved in these protocols. For instance, a browser-based security protocol for Single Sign-On (SSO in short) typically consists of a user (controlling a web browser), a Service Provider web site and an Identity Provider (who authenticates the user). Similarly, a browser-based security protocol for Cashier-as-a-Service (CaaS) scenario consists of a user, a Service Provider web site (e.g., an online store) and a Payment Service Provider (who authorizes payments).
The design and implementation of browser-based security protocols are usually so complex that several vulnerabilities are often present even after intensive inspection. This is witnessed, for example, by vulnerabilities found in various browser-based security protocols such as SAML SSO v2.0, OAuth Core 1.0, etc. even years after their publication, implementation, and deployment. Although techniques such as formal verification and white-box testing can be used to perform security analysis of browser- based security protocols, currently they have limitations: the necessity of having formal models that can cope with the complexity of web browsers (e.g., cookies, client-side scripting, etc.), the poor support offered for certain programming languages by white-box testing tools, to name a few. What remains is black-box security testing. However, currently available black-box security testing techniques for browser-based security protocols are either scenario-specific (i.e. they are specific for SSO or CaaS, not both) or do not support very well the detection of vulnerabilities enabling replay attacks (commonly referred to as logical vulnerabilities) and Cross-Site Request Forgery (CSRF in short).
The goal of this thesis is to overcome the drawbacks of the black-box security testing techniques mentioned above. At first this thesis presents an attack pattern-based black-box testing technique for detecting vulnerabilities enabling replay attacks and social login CSRF in multi-party web applications (i.e. web applications utilizing browser-based security protocols involving multiple parties). These attack patterns are inspired by the similarities in the attack strategies of previously-discovered attacks against browser-based security protocols. Second, we present manual and semi-automatic black-box security testing strategies for detecting 7 different types of CSRF attacks, targeting the authentication and identity management functionalities of web sites. We also provide proof-of-concept implementations of our ideas. These implementations are based on OWASP ZAP (a prominent, free and open-source penetration testing tool).
This thesis being in the context of an industrial doctorate, we had the opportunity to analyse the use-cases provided by our industrial partner, SAP, to further improve our approach. In addition, to access the effectiveness of the techniques we propose, we applied them against the browser-based security protocols of many prominent web sites and discovered nearly 340 serious security vulnerabilities affecting more than 200 web sites, including the web sites of prominent vendors such as Microsoft, eBay, etc
Strengthening of Soda-Borosilicate Glasses by Ion Exchange Processes
No full textFlexible electronics and displays rely on strong thin borosilicate glasses. Furthermore, borosilicate glass play a vital role in pharmaceutical packaging, particularly for the container of liquid medicine in the auto-injectors. Because of the risk of failure due to the fracture of the glass ampule the costumers need to purchase several units of auto-injector; also, the injector price increases dramatically. This renewed the interest in the strengthening of soda-borosilicate glass. Moreover, the applications of strong thin borosilicate glasses in flexible electronics attracted attention. Chemical strengthening is a practical means of improving the mechanical performance of soda borosilicate glasses. The chemical strengthening process involves the immersion of an alkali-silicate glass in a molten nitrate salt containing potassium ions at temperatures below the glass-transition temperature where the replacement of small alkali ions in the glass with larger potassium ions from the molten salt occurs. The glass composition, salts impurities, temperature and time, are crucial factors of the treatment. Furthermore, applying an electric field can speed up the process and improves the efficiency. This study investigates the impact of potassium for sodium ion exchange and its parameters on the final strength of alkali borosilicate glasses. Alkali borosilicate tubes, used in pharmaceutical packaging, were subjected to ion exchange in potassium nitrate salts containing different impurities. The initial surface flaws have a significant impact on the final strength due to the limited case depth of surface compression in alklai borosilicate glass subjected to ion exchange. Nonetheless, the results revealed that the sodium poisoning of salt has a limited influence on strengthening; conversely, even a small amount of calcium spoils the strengthening. The replacement of sodium ions with calcium is thermodynamically favoured with respect to Na/K ion-exchange. Calcium can penetrate into the glass surface and prevent the replacement of sodium with potassium and, consequently, the generation of compressive stress.
Interestingly, performing electric field assisted ion exchange, EF-IE, for 10 min produces an ion-exchanged layer as deep as conventional strengthening for 4 hours in soda borosilicate glass. Electric field assisted ion exchange also augments the glass strength and makes the glass more damage resistant; however, the initial defects on the glass surface have an adverse influence on the efficiency, as expected. Applying an electric field changes the governing mechanism of ion exchange and accelerates the penetration of potassium ions into the glass; furthermore, the glass structure of the layer undergone electric field assisted ion exchange is modified during the process. Although EF-IE generates a strong surface compression in glass, the inhomogeneous distribution of residual stress is a drawback. Performing EF-IE using AC E-fields produces homogenous ion-exchanged layers in glass and is, probably, a practical approach to balancing the residual stress in glass.
Chemical strengthening of a thin alkali-borosilicate glass ,D 263 Teco®, is also investigated in the present work. Na/K ion exchange improves the glass strength three times. Although the surface compression generated by ion-exchange in alkali borosilicate glasses is not as strong as typically used glasses for chemical strengthening ( alklai aluminosilicate), it can be used to improve the mechanical properties of borosilicate glass. Annealing prior to the ion exchange increases the compressive stress generated on the surface; however, its effect on strengthening is trivial.
The compressive stress produced by Na/K ion exchange in thin alkali borosilicate glass improves the damage resistance and the bending strength of glass. Due to the limited thickness of samples, heat treatments with high heating and cooling rates can be conducted. Such heat treatments can be used to carry out surface relaxation and improve the strength of samples by “surface relaxation”. A fast heat treatment after ion exchange improves the finals strength samples about 40%
Human Activity Analytics Based on Mobility and Social Media Data
Get PDFThe development of social networks such as Twitter, Facebook and Google+ allow users to share their beliefs, feelings, or observations with their circles of friends. Based on these
data, a range of applications and techniques has been developed, targeting to provide a better quality of life to the users. Nevertheless, the quality of results of the geolocationaware applications is signicantly restricted due to the tiny percentage of the social media data that is geotagged ( 2% for Twitter). Hence, increasing this percentage is an important and challenging problem. Moreover, information extracted from social media data can be complemented by the analysis of mobile phone usage data, in order to provide further insights on human activity patterns. In this thesis, we present a novel method for analyzing and geolocalizing non-geotagged Twitter posts. The proposed method is the rst to do so at the ne-grain of city neighborhoods, while being both eective and time ecient. Our method is based on the extraction of representative keywords for each candidate location,as well as the analysis of the tweet volume time series. We also describe a system built on top of our method, which geolocalizes tweets and allows users to visually examine the results and their evolution over time. Our system allows the user to get a better idea of how the activity of a particular location changes, which the most important keywords are, as well as to geolocalize individual tweets of interest. Moreover, we study the activity and mobility characteristics of the users that
post geotagged tweets and compared the mobility of users who attended the event with a random set of users. Interestingly, the results of this analysis indicate that a very small number of users (i.e., less than 35 users in this study) is able to represent the mobility patterns present in the entire dataset. Finally, we study the call activity and mobility patterns, clustering the observed behaviors
that exhibited similar characteristics, and characterizing the anomalous behaviors. We analyzed a Call Detail Record (CDR) dataset, containing (aggregated) information on
the calls among mobile phones. Employing density-based algorithms and statistical analysis, we developed a framework that identies abnormal locations, as well abnormal time intervals. The results of this work can be used for early identication of exceptional situations, monitoring the eects of important events in urban and transportation planning, and others
Nonstandard Models in Measure Theory and in functional Analysis
No full textThis thesis is concerned with the study of nonstandard models in measure theory and in functional analysis.
In measure theory, we define elementary numerosities, that are additive measures that take on values in a non-archimedean field and for which the measure of every singleton is 1. We have shown that, by taking the ratio with a suitable unit of measurement, from a numerosity it can be defined a non-atomic real-valued measure, and that every non-atomic measure can be obtained from a numerosity by this procedure. We then used numerosities to develop
a model for the probability of infinite sequences of coin tosses coherent with the original ideas of Laplace.
In functional analysis, we introduce a space of functions of nonstandard analysis with a formally finite domain, that extends both the space of distributions and the space of Young measures. Among the applications of this
space of functions, we develop a continuous-in-time, discrete-in-space nonstandard formulation for a class of ill-posed forward-backward parabolic equations, and on the study of the regularity and asymptotic behaviour of its nonstandard solutions. This approach proved to be a viable alternative to the study of the vanishing viscosity limit of the solution of a pseudoparabolic regularization of the original problem
Diseguali su quale base? Lo svantaggio scolastico dei figli di immigrati in Europa
No full textThe aim of this research is to analyse the educational gap between native and foreign students in Europe. In last decades, because of the increasing number of immigrants, the sociological literature on the ethnic stratification in education has considerably grown. However, several aspects of the relationship between ethnicity and educational inequality are still under debate. This research is based on the assumption that the gross educational disadvantage of foreign students is due to differences in both achievements and educational choices. I analyse the several dimensions that scholars have identified as being able to influence one of them, or both. The roles played by individual characteristics –micro-level– (such as: social class, cultural background, gender, ethnicity and migration background), by the school context –meso-level– (i.e. peers group, teachers, and the school) and by the institutional context –macro-level– (the educational system and the country’s migration history) will be analytically divided. As different European nations have historically attracted migrants from specific countries in specific periods, individual’s ethnicity has long coincided with his immigration generation. Nowadays, because of the growing number of nationalities present in each country, it is finally possible to separate these two dimensions. Thus, I add to the debate in that I analyse whether ethnicity and migration background influence the individual educational success independently one another and independently of social origins. Moreover, I address whether the relationship between ethnicity and educational inequality is due to primary or secondary effects. In other words, I investigate if ethnicity and migration background influence only academic competences – which than translate in better choices – or if they are also able to directly affect the latter, net of individuals academic skills
Terahertz Detectors and Imaging Array with In-Pixel Low-Noise Amplification and Filtering in CMOS technologies
No full textTerahertz gap corresponding to the frequency band of 0.3-3.0 THz is historically the last unexplored region of the electromagnetic spectrum left to be fully investigated. The major difficulty that has hampered the maturation of technologies operating in this region lies in the fact that much unlike its bordering millimeter and infrared regions, generation and detection of THz radiation is not trivial. Yet, such is the intriguing nature and properties of the terahertz radiations that the interest in this region has not faded. Infact, potential applications of THz based systems have emerged in various fields including biomedical imaging, safety and security, quality control and communication. Over the past decade, a lot of research work has been published with an aim to bridge this gap by both electronics and photonics based systems. While these attempts have succeeded to a certain extent, the available solutions either lack in terms of performance or are mostly bulky and difficult to integrate for portable and commercial purpose. This PhD dissertation focuses on the design and investigation of direct terahertz detectors which could be operated at room temperature and fabricated in standard silicon technologies, thereby making use of several advantages like high level of integration, low cost and small device size that these technologies have to offer. In particular, the emphasis is on developing and characterizing terahertz systems for imaging application by using field effect transistor devices as detectors. This objective is pursued in three parts. The first part (chapter 3) of the dissertation deals with the measurement and characterization challenges of terahertz systems. Unlike guided mode solutions, measurements of terahertz detectors and their systems require free space which presents several challenges due to atmospheric attenuation, spurious reflections and diffractions, beam shaping, and so on. Moreover, background noise is also significant considering that the detected signal is typically in the order of a few microvolts. In this regard, an overview of the most common techniques is given and a measurement methodology involving the use of a reference pyroelectric detector to measure the impinging input power and techniques for the evaluation of the detector under-test effective area is presented.
The second part (chapter 4) is related to the investigation of variants of antenna-coupled field effect transistor and schottky barrier diode in standard 180 nm CMOS process as examples of direct detectors. During laboratory characterization, detection of terahertz radiation from schottky diode could not be achieved due to matching issues. Moreover, optimization of schottky diode by modifying its standard cell proved to be challenging as compared to field effect transistor, which can be optimized easily to enhance performance parameters and was therefore finally chosen as the preferred choice. The final part of the thesis (chapters 5 and 6) concerns with the implementation of analog readout interface to perform signal processing of detected terahertz signal. First, a single pixel consisting of on-chip antenna-coupled detector and a switched capacitor based filtering operation is designed and fabricated in 0.15μm process. The pixel is tested by performing both electrical and terahertz characterization, achieving high voltage responsivity value of 470 kV/W and a minimum NEP of 480 pW/sqrt (Hz). The interface architecture is highly repeatable and it can be used with any commercially terahertz source, even if its operation is limited by low modulation frequency. On the basis of the successful measurement results, an 8 x 6 terahertz array for real-time imaging application is fabricated in the same technology by modifying the interface architecture to make it power and area efficient