Connections between the Sznajd model with general confidence rules and graph theory

The Sznajd model is a sociophysics model that is used to model opinion propagation and consensus formation in societies. Its main feature is that its rules favor bigger groups of agreeing people. In a previous work, we generalized the bounded confidence rule in order to model biases and prejudices in discrete opinion models. In that work, we applied this modification to the Sznajd model and presented some preliminary results. The present work extends what we did in that paper. We present results linking many of the properties of the mean-field fixed points, with only a few qualitative aspects of the confidence rule (the biases and prejudices modeled), finding an interesting connection with graph theory problems. More precisely, we link the existence of fixed points with the notion of strongly connected graphs and the stability of fixed points with the problem of finding the maximal independent sets of a graph. We state these results and present comparisons between the mean field and simulations in Barabasi-Albert networks, followed by the main mathematical ideas and appendices with the rigorous proofs of our claims and some graph theory concepts, together with examples. We also show that there is no qualitative difference in the mean-field results if we require that a group of size q > 2, instead of a pair, of agreeing agents be formed before they attempt to convince other sites (for the mean field, this would coincide with the q-voter model).

CLEANING ASSOCIATIONS BETWEEN BIRDS AND HERBIVOROUS MAMMALS IN BRAZIL: STRUCTURE AND COMPLEXITY

Birds that remove ectoparasites and other food material from their hosts are iconic illustrations of mutualistic-commensalistic cleaning associations. To assess the complex pattern of food resource use embedded in cleaning interactions of an assemblage of birds and their herbivorous mammal hosts in open habitats in Brazil, we used a network approach that characterized their patterns of association. Cleaning interactions showed a distinctly nested pattern, related to the number of interactions of cleaners and hosts and to the range of food types that each host species provided. Hosts that provided a wide range of food types (flies, ticks, tissue and blood, and organic debris) were attended by more species of cleaners and formed the core of the web. On the other hand, core cleaner species did not exploit the full range of available food resources, but used a variety of host species to exploit these resources instead. The structure that we found indicates that cleaners rely on cleaning interactions to obtain food types that would not be available otherwise (e.g., blood-engorged ticks or horseflies, wounded tissue). Additionally, a nested organization for the cleaner bird mammalian herbivore association means that both generalist and selective species take part in the interactions and that partners of selective species form an ordered subset of the partners of generalist species. The availability of predictable protein-rich food sources for birds provided by cleaning interactions may lead to an evolutionary pathway favoring their increased use by birds that forage opportunistically. Received 30 June 2011, accepted 10 November 2011.

Liberalism, Marxism and Democratic Theory Revisited: Proposal of a Joint Index of Political and Economic Democracy

Liberalism and Marxism are two schools of thought which have left deep imprints in sociological, political and economic theory. They are usually perceived as opposite, rival approaches. In the field of democracy there is a seemingly insurmountable rift around the question of political versus economic democracy. Liberals emphasize the former, Marxists the latter. Liberals say that economic democracy is too abstract and fuzzy a concept, therefore one should concentrate on the workings of an objective political democracy. Marxists insist that political democracy without economic democracy is insufficient. The article argues that both propositions are valid and not mutually exclusive. It proposes the creation of an operational, quantifiable index of economic democracy that can be used alongside the already existing indexes of political democracy. By using these two indexes jointly, political and economic democracy can be objectively evaluated. Thus, the requirements of both camps are met and maybe a more dialogical approach to democracy can be reached in the debate between liberals and Marxists. The joint index is used to evaluate the levels of economic and political democracy in the transition countries of Eastern Europe.

On some Banach space constants arising in nonlinear fixed point and eigenvalue theory

[EN] As is well known, in any infinite-dimensional Banach space one may find fixed point free self-maps of the unit ball, retractions of the unit ball onto its boundary, contractions of the unit sphere, and nonzero maps without positive eigenvalues and normalized eigenvectors. In this paper, we give upper and lower estimates, or even explicit formulas, for the minimal Lipschitz constant and measure of noncompactness of such maps.

Design, implementation and evaluation of a virtual laboratory for Computer Engineering Education

Broad consensus has been reached within the Education and Cognitive Psychology research communities on the need to center the learning process on experimentation and concrete application of knowledge, rather than on a bare transfer of notions. Several advantages arise from this educational approach, ranging from the reinforce of students learning, to the increased opportunity for a student to gain greater insight into the studied topics, up to the possibility for learners to acquire practical skills and long-lasting proficiency. This is especially true in Engineering education, where integrating conceptual knowledge and practical skills assumes a strategic importance. In this scenario, learners are called to play a primary role. They are actively involved in the construction of their own knowledge, instead of passively receiving it. As a result, traditional, teacher-centered learning environments should be replaced by novel learner-centered solutions. Information and Communication Technologies enable the development of innovative solutions that provide suitable answers to the need for the availability of experimentation supports in educational context. Virtual Laboratories, Adaptive Web-Based Educational Systems and Computer-Supported Collaborative Learning environments can significantly foster different learner-centered instructional strategies, offering the opportunity to enhance personalization, individualization and cooperation. More specifically, they allow students to explore different kinds of materials, to access and compare several information sources, to face real or realistic problems and to work on authentic and multi-facet case studies. In addition, they encourage cooperation among peers and provide support through coached and scaffolded activities aimed at fostering reflection and meta-cognitive reasoning. This dissertation will guide readers within this research field, presenting both the theoretical and applicative results of a research aimed at designing an open, flexible, learner-centered virtual lab for supporting students in learning Information Security.

Packet erasure correcting codes for wireless sensor networks: implementation and field trial measurements

This thesis regards the Wireless Sensor Network (WSN), as one of the most important technologies for the twenty-first century and the implementation of different packet correcting erasure codes to cope with the ”bursty” nature of the transmission channel and the possibility of packet losses during the transmission. The limited battery capacity of each sensor node makes the minimization of the power consumption one of the primary concerns in WSN. Considering also the fact that in each sensor node the communication is considerably more expensive than computation, this motivates the core idea to invest computation within the network whenever possible to safe on communication costs. The goal of the research was to evaluate a parameter, for example the Packet Erasure Ratio (PER), that permit to verify the functionality and the behavior of the created network, validate the theoretical expectations and evaluate the convenience of introducing the recovery packet techniques using different types of packet erasure codes in different types of networks. Thus, considering all the constrains of energy consumption in WSN, the topic of this thesis is to try to minimize it by introducing encoding/decoding algorithms in the transmission chain in order to prevent the retransmission of the erased packets through the Packet Erasure Channel and save the energy used for each retransmitted packet. In this way it is possible extend the lifetime of entire network.

Pseudodifferential analysis in Psi*-algebras on transmission spaces, infinite solving ideal chains and K-theory for conformally compact spaces

The present thesis is a contribution to the theory of algebras of pseudodifferential operators on singular settings. In particular, we focus on the $b$-calculus and the calculus on conformally compact spaces in the sense of Mazzeo and Melrose in connection with the notion of spectral invariant transmission operator algebras. We summarize results given by Gramsch et. al. on the construction of $Psi_0$-and $Psi*$-algebras and the corresponding scales of generalized Sobolev spaces using commutators of certain closed operators and derivations. In the case of a manifold with corners $Z$ we construct a $Psi*$-completion $A_b(Z,{}^bOmega^{1/2})$ of the algebra of zero order $b$-pseudodifferential operators $Psi_{b,cl}(Z, {}^bOmega^{1/2})$ in the corresponding $C*$-closure $B(Z,{}^bOmega^{12})hookrightarrow L(L^2(Z,{}^bOmega^{1/2}))$. The construction will also provide that localised to the (smooth) interior of Z the operators in the $A_b(Z, {}^bOmega^{1/2})$ can be represented as ordinary pseudodifferential operators. In connection with the notion of solvable $C*$-algebras - introduced by Dynin - we calculate the length of the $C*$-closure of $Psi_{b,cl}^0(F,{}^bOmega^{1/2},R^{E(F)})$ in $B(F,{}^bOmega^{1/2}),R^{E(F)})$ by localizing $B(Z, {}^bOmega^{1/2})$ along the boundary face $F$ using the (extended) indical familiy $I^B_{FZ}$. Moreover, we discuss how one can localise a certain solving ideal chain of $B(Z, {}^bOmega^{1/2})$ in neighbourhoods $U_p$ of arbitrary points $pin Z$. This localisation process will recover the singular structure of $U_p$; further, the induced length function $l_p$ is shown to be upper semi-continuous. We give construction methods for $Psi*$- and $C*$-algebras admitting only infinite long solving ideal chains. These algebras will first be realized as unconnected direct sums of (solvable) $C*$-algebras and then refined such that the resulting algebras have arcwise connected spaces of one dimensional representations. In addition, we recall the notion of transmission algebras on manifolds with corners $(Z_i)_{iin N}$ following an idea of Ali Mehmeti, Gramsch et. al. Thereby, we connect the underlying $C^infty$-function spaces using point evaluations in the smooth parts of the $Z_i$ and use generalized Laplacians to generate an appropriate scale of Sobolev spaces. Moreover, it is possible to associate generalized (solving) ideal chains to these algebras, such that to every $ninN$ there exists an ideal chain of length $n$ within the algebra. Finally, we discuss the $K$-theory for algebras of pseudodifferential operators on conformally compact manifolds $X$ and give an index theorem for these operators. In addition, we prove that the Dirac-operator associated to the metric of a conformally compact manifold $X$ is not a Fredholm operator.

Coordination and Control of Autonomous Mobile Robots Swarms by using Particle Swarm Optimization Algorithm and Consensus Theory

This thesis presents some different techniques designed to drive a swarm of robots in an a-priori unknown environment in order to move the group from a starting area to a final one avoiding obstacles. The presented techniques are based on two different theories used alone or in combination: Swarm Intelligence (SI) and Graph Theory. Both theories are based on the study of interactions between different entities (also called agents or units) in Multi- Agent Systems (MAS). The first one belongs to the Artificial Intelligence context and the second one to the Distributed Systems context. These theories, each one from its own point of view, exploit the emergent behaviour that comes from the interactive work of the entities, in order to achieve a common goal. The features of flexibility and adaptability of the swarm have been exploited with the aim to overcome and to minimize difficulties and problems that can affect one or more units of the group, having minimal impact to the whole group and to the common main target. Another aim of this work is to show the importance of the information shared between the units of the group, such as the communication topology, because it helps to maintain the environmental information, detected by each single agent, updated among the swarm. Swarm Intelligence has been applied to the presented technique, through the Particle Swarm Optimization algorithm (PSO), taking advantage of its features as a navigation system. The Graph Theory has been applied by exploiting Consensus and the application of the agreement protocol with the aim to maintain the units in a desired and controlled formation. This approach has been followed in order to conserve the power of PSO and to control part of its random behaviour with a distributed control algorithm like Consensus.

Design, implementation and performance evaluation of an anonymous distributed simulator

La simulazione è definita come la rappresentazione del comportamento di un sistema o di un processo per mezzo del funzionamento di un altro o, alternativamente, dall'etimologia del verbo “simulare”, come la riproduzione di qualcosa di fittizio, irreale, come se in realtà, lo fosse. La simulazione ci permette di modellare la realtà ed esplorare soluzioni differenti e valutare sistemi che non possono essere realizzati per varie ragioni e, inoltre, effettuare differenti valutazioni, dinamiche per quanto concerne la variabilità delle condizioni. I modelli di simulazione possono raggiungere un grado di espressività estremamente elevato, difficilmente un solo calcolatore potrà soddisfare in tempi accettabili i risultati attesi. Una possibile soluzione, viste le tendenze tecnologiche dei nostri giorni, è incrementare la capacità computazionale tramite un’architettura distribuita (sfruttando, ad esempio, le possibilità offerte dal cloud computing). Questa tesi si concentrerà su questo ambito, correlandolo ad un altro argomento che sta guadagnando, giorno dopo giorno, sempre più rilevanza: l’anonimato online. I recenti fatti di cronaca hanno dimostrato quanto una rete pubblica, intrinsecamente insicura come l’attuale Internet, non sia adatta a mantenere il rispetto di confidenzialità, integrità ed, in alcuni, disponibilità degli asset da noi utilizzati: nell’ambito della distribuzione di risorse computazionali interagenti tra loro, non possiamo ignorare i concreti e molteplici rischi; in alcuni sensibili contesti di simulazione (e.g., simulazione militare, ricerca scientifica, etc.) non possiamo permetterci la diffusione non controllata dei nostri dati o, ancor peggio, la possibilità di subire un attacco alla disponibilità delle risorse coinvolte. Essere anonimi implica un aspetto estremamente rilevante: essere meno attaccabili, in quanto non identificabili.

Harry Potter and the Theory of Things

This thesis investigates the boundaries between body and object in J.K. Rowling’s Harry Potter series, seven children’s literature novels published between 1997 and 2007. Lord Voldemort, Rowling’s villain, creates Horcruxes—objects that contain fragments of his soul—in order to ensure his immortality. As vessels for human soul, these objects rupture the boundaries between body and object and become “things.” Using contemporary thing theorists including John Plotz and materialists Jean Baudrillard and Walter Benjamin, I look at Voldemort’s Horcruxes as transgressive, liminal, unclassifiable entities in the first chapter. If objects can occupy the juncture between body and object, then bodies can as well. Dementors and Inferi, dark creatures that Rowling introduces throughout the series, live devoid of soul. Voldemort, too, becomes a thing as he splits his soul and creates Horcruxes. These soulless bodies are uncanny entities, provoking fear, revulsion, nausea, and the loss of language. In the second chapter, I use Sigmund Freud’s theorization of the uncanny as well as literary critic Kelly Hurley to investigate how Dementors, Inferi, and Voldemort exist as body-turned-object things at the juncture between life and death. As Voldemort increasingly invests his immaterial soul into material objects, he physically and spiritually degenerates, transforming from the young, handsome Tom Marvolo Riddle into the snake-like villain that murdered Harry’s parents and countless others. During his quest to find and destroy Voldemort’s Horcruxes, Harry encounters a different type of object, the Deathly Hallows. Although similarly accessing boundaries between body/object, life/death, and materiality/immateriality, the three Deathly Hallows do not transgress these boundaries. Through the Deathly Hallows, Rowling provides an alternative to thingification: objects that enable boundaries to fluctuate, but not breakdown. In the third chapter, I return to thing theorists, Baudrillard, and Benjamin to study how the Deathly Hallows resist thingification by not transgressing the boundaries between body and object.