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Cooperative Push/Pull Protocols for Live Peer-Assisted Streaming
No full textVideo streaming is rapidly becoming one of the key services of the Internet. Most streaming is today "on demand" and delivered via unicast delivery; however, many applications require delivery to many end-users and the lack of ubiquitous IP multicast remains a weakness of the Internet.
Given this scenario, the peer-to-peer (P2P) or peer-assisted communications is an appealing solution, especially in light of its intrinsic scalability and its extremely low initial investment requirements. However, the design of efficient, robust, and performing P2P streaming systems remains a high challenge, in particular when real-time (hard or soft) constraints are part of the service quality, as in TV distribution or conferencing.
This thesis deals with P2P live streaming, concentrating on unstructured, swarm-based systems. The protocols explored and proposed are based in general on mixed Push/Pull phases, i.e., the behavior of peers alternates between offering content to other peers and seeking the content from other peers.
The first part of the work is dedicated to the analysis of the fundamental properties of the Push/Pull protocols, including the enhancement of base protocols with a chunks' negotiation phase, which enable peers to execute parallel communications at the same time, fully exploiting their resources and drastically reducing duplicates and waste. Next, the focus is shifted on the impact of network parameters in video streaming distribution, showing that promoting locality in interactions leads to better performance than selecting target peers randomly.
Then, the attention is focused on wireless scenarios by mixing local multicast techniques (based on a modified version of the Protocol Independent Multicast --PIM-- adapted to wireless environments) with active Pull recovery of missing data, with a peer-assisted approach. This protocol, called PullCast, enables end-users to pull missed data packets via unicast communications while they receive video packet in multicast via push, exhibiting interesting results in terms of chunks diffusion delay and fraction of end-users served.
Finally, the GRAPES library is introduced to provide a set of open-source components conceived as basic building blocks for developing new P2P streaming applications which have in mind the intelligent usage of network resources as well as the Quality of Experience of final users.
GRAPES is the core library behind PeerStreamer, an open source P2P media streaming framework developed under the NAPA-WINE European research project, and currently supported by the EIT ICT Labs
Il corretto equilibrio dei poteri tra amministratori e soci nelle società quotate
No full textCon d.lgs. 27 febbraio 2010, n. 27 è stata finalmente recepita nell’ordinamento italiano la Direttiva 2007/36/CE dell’11 luglio 2007 relativa all'esercizio di alcuni diritti degli azionisti di società quotate, a mezzo della quale il legislatore europeo – nella convinzione, poi ribadita nel Libro Verde Il quadro dell’Unione europea in materia di governo societario del 5 aprile 2011, che l’implementazione dei diritti degli azionisti di società quotate possa incentivarne l’attivismo e facilitare quindi il controllo assembleare sull’operato dell’organo gestorio – detta svariate disposizioni volte ad agevolare l’esercizio di alcuni diritti amministrativi dei soci, in particolare il diritto di voto in assemblea.
Questo orientamento legislativo mira in ultima istanza all’ambizioso risultato di ribilanciare a vantaggio dei soci il rapporto tra proprietà e gestione, che i recenti scandali finanziari hanno dimostrato essere eccessivamente squilibrato a favore del management, e così a favorire il «buon governo societario».
La Direttiva Shareholders’ Rights appare invero uno strumento inidoneo a stimolare un significativo attivismo assembleare, perché le misure di cui all’intervento legislativo comunitario – certamente apprezzabili ove prevedono, inter alia, la possibilità per i soci di iscrivere punti all’ordine del giorno nonché di porre domande alla società e ricevere risposte, e ove riducono gli ostacoli materiali che dissuadono l’azionista dal votare e gli oneri connessi al difficile reperimento di informazioni rilevanti in vista dell’assemblea – non incidono sugli elevati costi informativi connessi allo studio delle informazioni, prerequisito indispensabile per una partecipazione consapevole alle attività assembleari; la “piena” partecipazione continua a rappresentare dunque un’alternativa eccessivamente onerosa e antieconomica – e quindi impraticabile – rispetto alle alternative per ridurre il rischio connaturato nell’investimento invalse nella prassi, quali la diversificazione dei portafogli azionari. Questa e altre considerazioni in ordine al comportamento degli investitori istituzionali nei mercati finanziari portano in definitiva a concludere che le nuove misure tese alla valorizzazione del ruolo dei soci non offrono un’alternativa percorribile rispetto alle politiche orientate alla c.d. apatia razionale.
Una terza via rispetto all’equilibrio fondato sulla centralità e libertà operativa del management (rivelatasi fallimentare alla prova dei fatti, in quanto priva di idonei contrappesi) o sulle potenzialità (inespresse e solo utopisticamente esprimibili) dei soci quali diretti controllori degli amministratori, è rappresentata dalla valorizzazione del ruolo – ab origine svilito e comunque mai pienamente estrinsecatosi nonostante il succedersi delle riforme intervenute, specie in tema di società quotate dell’organo di controllo interno: valorizzazione che non può prescindere da un ripensamento del significato del requisito dell’indipendenza dei sindaci e del contributo che in tal senso promana dalla partecipazione delle minoranze all’elezione dell’organo. Proprio la percezione di una maggiore indipendenza del collegio sindacale rispetto al passato, e del ruolo chiave degli investitori nell’assicurare tale indipendenza, auspicabilmente condurrà al raggiungimento dell’obiettivo ultimo del legislatore europeo, ovvero il ripristino della fiducia del pubblico dei risparmiatori nei mercati finanziari
Structural Defects in Nanotechnology: Production, Characterization, Applications: Transport Properties in Mechanically Ground Nanocrystalline Ceramics & Hydrogen Storage in Metallic Hydrides
No full textStructural defects play a major role in nanotechnology as they influence most properties, thus largely motivating the special interest in studying materials at the nano scale. The present Thesis work contributes to this broad and diversified research field with emphasis on the characterization of nanocrystalline ceramic materials and their lattice defects. In particular, main efforts were addressed to develop new and more comprehensive approaches to the study of nanocrystalline powders, combining different techniques for a better and deeper understanding of materials.
The specific applications selected in this work are basically two: nanocrystalline fluorite as a promising ionic conductor and nanocrystalline magnesium hydride for hydrogen storage applications. Chapters II and III were dedicated to investigate nanocrystalline fluorite produced by two different methods: a bottom-up approach based on co-precipitation of Ca and F precursors yielding loosely bound nanocrystals, and a popular top-down approach, high energy ball milling, giving nanocrystals of comparable sizes but strongly agglomerated and densely populated with dislocations. As a major achievement reported in this part of the Thesis work, a new approach was proposed and tested for the simultaneous modelling of X-ray Diffraction (XRD) peak profiles and solid state NMR spin-lattice relaxation data. With the valuable support of Transmission Electron Microscopy (TEM), this work offers a new understanding of the complex defect structure of nanocrystalline fluorite, and is also a demonstration of the power of combining different techniques in a consistent way.
One of the most debated aspects of nanotechnology concerns the stability of the nanostructure, and the mechanisms of defect annealing and grain growth with temperature. This topic was the object of chapter V, dedicated to study the influence of lattice defects on the grain growth kinetics of nanocrystalline fluorite. This chapter was preceded by chapter IV, on the furnace recently installed at the MCX beamline for in-situ high temperature fast data collection; besides providing useful details for the in-situ study on nanocrystalline fluorite shown in the following chapter, the activity reported in chapter IV is a tangible sign of the special involvement during the Thesis work in supporting standard operation as well as development of the ELETTRA beamline MCX. The growth kinetics was studied on two samples, among those discussed in Chapter III, with comparable crystalline domain size but drastically different lattice defect content, so to highlight the role lattice defects – dislocations in this case – in the growth process.
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Last two chapters (chapter VI and VII) were dedicated to nanocrystalline magnesium hydride, and how the performance, in particular the hydrogen desorption kinetics, can be improved by adding a nanocrystalline tin oxide. Besides general aspects on phase composition of the system and hydrogen storage capability, the work also addressed the problem of obtaining activation energy values in the thermal decomposition of magnesium hydride powders, presenting an interesting review of results given by the most known and well-assessed TG-MS coupled measurements, with details on the use of different equations of the literature on thermal analysis.
Although research work can rarely be considered as finished, a sound conclusion of this Thesis work is toward the use of different characterization techniques, also within the same data analysis procedure, to support a better, and more reliable investigation of nanomaterial properties
The Impact of European Union Asylum Policy on Domestic Asylum Policy in Germany and Britain: 1990-2007
No full textOver the past two decades, the European Union has taken important steps towards the establishment of a common European asylum policy. The question of the impact of this cooperation on domestic asylum policy has so far received surprisingly little attention. Most explanations have focused on how an agreement on restrictive policies was achieved at EU level, and assumed a relatively unproblematic implementation of these measures domestically. More recently, some scholars have contested these explanations by emphasizing the rights-enhancing effects of recent EU asylum policy legislation.
This thesis argues that rather than focusing on the question of whether EU cooperation increases or decreases domestic asylum policy standards, we should focus on explaining how EU asylum policy affects domestic asylum policy. The question can only be addressed satisfactorily if the inter-related processes of arriving at these policies at EU level and implementing them domestically are taken into account.
The theoretical account proposed here conceives of preferences as the crucial variable connecting the processes of uploading and downloading. The main argument of this thesis is that governments try to project their policy preferences which reflect their desire to change or retain domestic status quo and to download policies in accordance with these preferences. At the EU level, governments seek to upload or support policies in line with their domestically-shaped preferences and oppose those which contradict them or at least seek flexibility allowing them to maintain existing policies. At the national level, states download EU policy selectively, in line with their domestically-shaped preferences, leading to over-implementing, under-implementing or not implementing certain provisions.
In addition, the thesis locates the sources of these preferences on asylum policy in public opinion, party ideology, and the number of asylum seekers. The dissertation shows that issue salience in the media and among the general public affects the relationship between these variables.
Depending on the political-institutional context, the factors identify above interact with each other, resulting in differential impact of EU asylum policy on domestic policy. The thesis distinguishes between simple and compound polities, and shows how they differ in their responsiveness to the variables identified above, in the frequency and stability of reforms, and in the way they use the EU to facilitate domestic change. It also demonstrates that in compound polities preferences are mostly influenced by party ideology while in simple ones they are more likely to reflect public opinion.
In order to trace the impact of EU cooperation in asylum policy on domestic policy, this dissertation employs process tracing and a three-step analytical framework which encompasses preference formation, EU-level negotiations and implementation. Such framework allows us to answer the question of the impact of EU asylum policy on national ones without under- or overstating the role of the EU. The dissertation applies this framework to study all major EU asylum policy agreements adopted between 1990 and the completion of the first phase of the Common European Asylum System in 2007, and their impact in Germany and Britain
Mathematical modelling of transport across blood vessel walls
No full textThe last decade has seen an increasing interest in bio-mathematical modelling and scientific computing, resulting in new applications to relevant physiological phenomena and to a better understanding of the origin of various diseases. A topic of great interest to several degenerative diseases is filtration across microvessel walls.
The role of the microvessel wall is to let oxygen and nutrients contained in the blood stream to reach the interstitium, and ultimately the surrounding cells, while blocking macromolecules. An understanding of these processes is important in preventing and curing neuro-degenerative diseases, as well as for exploring possible mechanisms to make drug delivery more efficient.
This work presents a one-dimensional, time dependent mathematical model describing transport of blood plasma and macromolecules across blood vessel walls. The model takes into account the heterogeneous microvessel wall composition, in order to accurately describe trans-vascular flow. This results in a multi-layered domain, accounting for variable physical properties across the layers forming the micro-vascular wall. In particular, the glycocalyx and endothelium, accounted for in many biological studies, are represented in our model.
This micro-structural, yet simplified description of the vascular wall, allows us to simulate the effect of glycocalyx damage and of other pathologies, such as hypertension, hemorrhage and hypovolemia, both in steady and time-dependent states.
Due to the simplicity, and thus efficiency of the proposed model, simulations are fast and provide results which are in line with published experimental studies. Furthermore, the simulation tool may be useful for practical applications in physiological and medical studies, by evaluating the possible consequences of pathological conditions
An Innovative Methodological Approach Based on Compressive Sensing for the Synthesis and Control of Antenna Arrays
No full textIn the framework of antenna array synthesis and control, this thesis focus on the development and analysis of techniques based on the Bayesian Compressive Sensing (BCS) for the design of sparse antenna arrays and for the estimation of the direction of arrival (DoA) of signals impinging on an antenna array. After formulating the sparse-array synthesis problem in a probabilistic fashion, the single-task BCS (ST-BCS) is applied to the synthesis of symmetrical antenna arrays with real weights. In order to deal with the synthesis of sparse arrays with complex weights, the multitask version of the BCS (MT-BCS) is employed to correlate the real and imaginary part of the resulting excitation distribution. Concerning the DoA estimation problem, starting from the observation that the signals impinging on the antenna array are sparse in the spatial domain, a single-snapshot ST-BCS -based technique is proposed. Moreover, the MT-BCS -based extension of this technique is introduced in order to enhance the quality of the estimations through the exploitation of the correlation among different snapshots. In the numerical validation, an exhaustive analysis has been performed to assess effectiveness, reliability, but also limitations of the proposed methodologies. Comparisons with state-of-the-art are reported and discussed, as well
Domain Specific Mashup Platforms as a Service
No full textSince the Web 2.0 advent, Web users have gained more and more power moving their role from simple information consumers to producers. In line with this trend, mashup technologies have immediately attracted a lot of attention and many research investments since their birth. The big mashup promise was to bring application development to the masses, so that any Web-educated worker, also non-IT skilled, could implement his/her own situational applications (i.e., relatively small applications meant to address a temporary need of one or few persons) exploiting the simple paradigms and visual metaphors provided by mashup tools. After a decade from the first mashup tools, though, mashups are not really part of people’s everyday life and are still rather unknown technologies that — beside some exceptions — hardly find concrete application in the real world.
During our research in this field our high-level goal was to foster the adoption of mashup technologies by end users. Aiming at this, we identified three main characteristics that must be reached by mashup technologies to get to the expected diffusion: (i) usefulness and (ii) usability for the end users and (iii) affordability for the developers of the respective mashup tools (in terms of required skills, time and cost). We identified lacks in these achievements as main hindering factors for the wide adoption of mashup technologies. Making mashup technologies useful, usable and affordable, therefore, are the three main challenges we addressed in our research work. This work contributes to the achievement of all these three major goals: first, by enabling a so-called universal integration paradigm, focussing on the creation of more powerful and complete mashups allowing data, application logic and user interface integration in one single language and tool; then, by introducing and developing domain specific mashup technologies, able to lower mashups’ complexity and make them usable by domain experts (i.e., end users expert of a given target domain); finally, by realizing a system able to generate domain specific mashup platforms as a service, basically relieving developers of platforms implementation and, therefore, making platform development affordable. This thesis specifically focusses on the last two points, i.e., on the domain specific mashup approach and on the semi-automatic generation of domain specific mashup platforms
L'imprenditoria cinese in Italia: due casi studio: la ristorazione cinese a Milano e il distretto del porfido a Trento
No full textQuesto lavoro è uno studio accurato su due settori economici che hanno visto, con modalità differenti, lo sviluppo dell'imprenditoria cinese: la ristorazione cinese a Milano e il distretto del porfido a Trento. La metodologia di ricerca impiegata è stata l'etnografia con la conduzione di interviste semi-strutturate a 56 migranti cinesi, tra lavoratori dipendenti ed autonomi, e interviste non strutturate a 17 esperti incontrati nei due contesti territoriali. I risultati di tale studio riguardano il ruolo delle reti etniche cinesi nel favorire l'accesso al mercato del lavoro e l'imprenditoria, ma anche il contesto lavorativo cinese, le problematiche legate alla normativa contrattuale e i rapporti intra-familiari e tra i membri della rete etnica in ambito familiare e lavorativo
Indirect Expropriation in International Investment Law
No full textRegulating indirect expropriation in international investment law is a challenging task for investment tribunals. No universally agreed definition of the concept exists and international investment treaties (IITs) provide a defective legal framework––paralleled to that of expropriation tout court––to govern the issue. This work contributes to the discourse on indirect expropriation in international investment law by elaborating upon existing literature and scholarship and by examining judicial and arbitral decisions. It suggests an alternative interpretative framework useful to the analysis and decision of international expropriatory cases. To this end, the research adopts an inductive methodology. In light of the decisions of several international fora, the study examines the concept of property (Chapter IV), the concept of taking (Chapter V), the lawfulness or unlawfulness of expropriation (Chapter VI) and the concept of public purpose (Chapter VII) which are deemed as the constitutive elements of the customary international law definition of expropriation to which the concept of indirect expropriation is paralleled in international treaty-law (and practice).
The study begins with the analysis of the German and the American domestic experiences on takings in view of the influence that such constitutional and administrative systems have exerted on the development of international criteria and standards for deciding ‘international taking issues’. It is here argued that a comparative approach to indirect takings issues may shed light on current interpretative obstacles faced by arbitral tribunals, chief of which is the lack of an international consensus about the function of property at the international level.
A reconceptualization of indirect expropriation as unlawful de facto expropriation is advocated as a prospect for future developments. The adjective indirect is deemed superfluous and it is claimed that non-expropriatory interferences with property rights are to be sanctioned by means of other substantive standards of protection. Such reconceptualization aims at removing trivial categories and misleading labels thus far employed to describe indirectly expropriatory measures and suggests to focus on the actual variables at stake––compensable expropriation vis-à-vis non-compensable regulation by the host State. In addition, a degree of deference to host States is also advised for, to the extent that provisions in IITs are stipulated in a more specific manner that duly defines legitimate regulatory purposes and takes into account the consequences of a State’s unlawful conducts. This would reduce adjudicators’ discretion in the exercise of their interpretative powers.
This study cannot and aims not at answering the question concerning where to draw a dividing line between regulation and compensable (indirect) expropriation. This is deemed to remain a case-by-case decision of investment tribunals. Rather, by drawing from both international and national models, the proposed interpretative framework would reconcile or guide arbitral approaches to takings issues towards the development of an intelligible legal methodology
On Social Overlays and Their Application to Decentralized Online Social Networks
No full textOver the last decade, Online Social Networks (OSNs) have attracted hundreds of millions of users worldwide, establishing themselves as one of most successful communication tools to date. Yet, the business model adopted by current centralized approaches makes them inherently prone to privacy issues and hostile to openness, as service providers rely on the commercial exploitation of their userbases' private data as their means of survival. We believe, as others do, that decentralization could represent a solution to this fundamental problem.
In this work, we propose a novel P2P approach to decentralized OSNs in which peers are organized as a social overlay (SO): an overlay network that effectively mirrors an underlying social network by constraining communication to pairs of peers whose owners are friends. SOs are special in two ways. First, by embodying friendship in their links, SOs can help us either solve or mitigate fundamental trust-related issues that arise in P2P systems. Second, SOs exhibit an inherent compatibility towards OSNs, a result of the former being shaped after human communication, and the latter being human communication tools. These give raise to an inherent potential for synergy, which we propose to reap by means of a simple approach that provides a key functionality of modern OSNs: profile-based communication.
In our approach, nodes cache the profile pages of their friends locally, and updates get proactively disseminated only by trusted nodes, over a user's ego network: the subgraphs of social networks composed by a user, her friends, and the connections among them. The contributions of this thesis then emerge as we tackle this seemingly simple problem of update dissemination over ego networks and, along the way, uncover issues that lead us to progressively deeper problems and understanding, and, ultimately, to effective solutions.
In the first part of this thesis, we explore the use of push gossip protocols as the means to achieve efficient dissemination of updates over ego networks. We show that mainstream gossip protocols cannot be applied in this context, due to the largely non-uniform structure of ego networks. By taking these structural properties into account, we develop a novel gossip protocol that is able to adapt to, and leverage this non-uniformity, providing efficient and timely dissemination of updates.
The study of these dissemination protocols under peer churn leads us to uncover the second problem we tackle in this thesis -- namely, the network-induced communication delays that emerge from the interaction of the social graph with the underlying peer dynamics. By means of a small-scale simulation study, we find that not only these delays can be rather extreme, but that they matter more than the underlying dissemination protocol on the long run. While this realization is in itself a contribution, we also find that evaluating the problem in more depth, as well as identifying opportunities for improvement, cannot be done by simulations alone. This is due to three factors: i) the size of the target networks under study, ii) the large parameter space inherent to availability modelling, and iii) the large number of repetitions required for obtaining good quality estimators. Put together, these translate into prohibitive costs.
We therefore propose a novel hybrid analytical/simulation framework that enables the estimation of dissemination delays at a practical cost. In the third part of this thesis, we show how to further develop this framework by deriving analytical, closed-form expressions that describe delays as a function of a graph and availability parameters, when the underlying availability model is based on a certain class of simpler distributions.
Finally, by putting together the lessons we learnt along the way -- our dissemination protocol and the knowledge we acquired about the workings of communication delays -- we devise the final contribution of this thesis: a hybrid, cloud-assisted P2P architecture that enables efficient dissemination in social overlays under churn. This solution, as we show, provides performance that rivals that of centralized solutions, while incurring modest economical costs