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In this work, we explore the role of immigrant-critical alternative media in shaping collective emotions and users' evaluations of the immigration issue, using a conversational approach and an empirical case of Flashback, a prominent Swedish online platform where many immigration-related discussions take place. Our text and network-based analysis of more than 9,000 conversations during the last election period reveals that the platform users consume and distribute diverging types of media content across a wide ideological spectrum which, however, has a limited influence on the evolution of conversations and users' stances in the immigration debate. Nevertheless, we find that the conversation networks with alternative media content tend to include more negative evaluations of the immigration issue, attracting fewer participants and lasting less than other conversations. We contextualise our findings using Collins' Interaction Ritual Chains (IRC) theory and discuss the conditions under which such online conversations can produce high user involvement and, potentially, participants' radicalisation.

This paper proposes to use MeetUp data to study the emergence and the evolution of the technological trend commonly known as Internet of Things (IoT). Starting from a manually selected sample of 220 European MeetUp groups we used MeetUp's APIs, to retrieve additional information about the events and participating users. The final dataset consists of 220 groups, 32967 members and 2386 events from 2011 until now (Jan 2019). The results suggest the presence of clearly identifiable European hubs for IoT development but a worldwide crowd of users. From a temporal perspective the MeetUp data shows how IoT exploded in 2015 and how it might have peaked in 2017. Within this period of time IoT has not been a “stable technology” but as evolved incorporating, within its area of “related topics” new and emerging technologies such as Cryptocurrency or cloud computing.

Large bandgaps with low transmission in 3D macroporous silicon photonic crystals have been proved as an interesting technology for the development of optical filters and spectroscopic MIR gas sensors. The aim of this study is the investigation of different bandgap widening methods based on multiperiodic structures for 3D macroporous silicon photonic crystals. To do so, chirped modulations and structures with different periodicity groups have been modelled and theoretically analysed by means of 3D FDTD simulations. They have revealed that by using different decreasing periodicity groups, bandgaps with null transmission and widths as high as 1800 nm, 4 times the original single periodicity photonic crystal bandgap, can be obtained. Furthermore, it has been shown that a resonant cavity with a 20% transmission can be placed in a 1 µm wide bandgap. The results open a way to use this type of structures not only for gas sensing but also for other purposes such as wide stop-band filters, selective filters or broadband mirrors., Peer Reviewed, Postprint (published version)

A macroporous silicon photonic crystal is designed and optimized theoretically for its use in gas sensing applications and IR optical filters. Light impinges perpendicularly onto the sample surface (vertical propagation) so a three-dimensional (3d) structure is used. For gas sensing, a sharp resonance is desired in order to isolate an absorption line of the gas of interest. The high Q-factors needed mandate the use of a plane defect inside the PhC to give rise to a resonant mode inside the bandgap tuned to the gas absorption line. Furthermore to allow gas passage through the device, an open membrane is required. This can affect the mechanical resilience. To improve the strength of the photonic crystal the pores are extended after the “active” 3d part. The number of modulations, and the extension length have been optimized to obtain the largest Q-factor with reasonable transmitted power. These proposed structures have been experimentally performed, probing an enhancement of almost an order of magnitude in the Q-factor in respect with the basic case. Simulations considering CO2 have been performed showing that the proposed structures are promising as precise optical gas sensors., Peer Reviewed, Postprint (author's final draft)

The final publication is available at Springer via http://dx.doi.org/10.1007/s13278-016-0346-9., We rethink and extend the concepts of position and role in a network, basing them on various well-known measures that were not previously associated with these concepts, such as geodesic distance and modularity. The effectiveness of our new role and position detection algorithms is evaluated both qualitatively and quantitatively, on synthetic and real data, showing that we can identify new types of meaningful patterns in networks., Peer Reviewed, Postprint (published version)

Cloud services in community networks have been enabled by micro-cloud providers. They form community network micro-clouds (CNMCs), which grow organically, i.e. without being planned and optimized beforehand. Services running in community networks face specific challenges intrinsic to these infrastructures, such as the limited capacity of nodes and links, their dynamics and geographic distribution. CNMCs are used to deploy distributed applications, such as streaming and storage services, which transfer significant amounts of data between the nodes on which they run. Currently there is no support given to users for enabling them to chose better or the best option for specific service deployments. This paper looks at the next step in community network cloud service deployments, by taking network characteristics into account when deciding placement of service instances. We propose a service placement algorithm (PASP) that minimizes the service overlay diameter, while fulfilling service specific criteria. First, we characterize with simulations the potential performance gains of our approach. Secondly, we apply our algorithm to deploy a distributed storage service currently used in Guifi.net, and evaluate it in the real production network, assessing the performance and effects of our algorithm. We find that our PASP algorithm reduces the client reading times by an average of 16% (with a max. improvement of 31 %) compared to the currently used organic placement scheme. Our results show how the choice of an appropriate set of nodes, taken from a larger resource pool, can influence service performance significantly., Peer Reviewed, Postprint (published version)

Collaborative learning activities have shown to be useful to address educational processes in several contexts. Monitoring these activities is mandatory to determine the quality of the collaboration and learning processes. Recent research works propose using Social Network Analysis techniques to understand students' collaboration learning process during these experiences. Aligned with that, this paper proposes the use of the indirect blockmodeling network analytic technique for monitoring the behaviour of different social roles played by students in collaborative learning scenarios. The usefulness of this technique was evaluated through a study that analysed the students' interaction network in a collaborative learning activity. Particularly, we tried to understand the structure of the interaction network during that process. Preliminary results suggest that indirect blockmodeling is highly useful for inferring and analysing the students' social roles, when the behaviour of roles are clearly different among them. This technique can be used as a monitoring service that can be embedded in collaborative learning applications., Peer Reviewed, Postprint (published version)

QPides! is an application whose main target is to satisfy the need of a more fluid and detailed information between restaurants and their clients. This information includes the restaurant's location, table allocation, availability, menu content and the customers' comments. Additionally, provides a reliable and secure channel to submit customized orders and payments. This enables to reduce the workload on restaurant staff and invest such resources in maximizing the quality of the service provided. One of the most important distinguishing features of QPides! application is the table allocation process, since an effective table allocation can be crucial to a restaurant's profitability. Inefficient use of tables means that the restaurant is losing potential customers, but overbooking means that customers are delayed or feel cramped, and so are unlikely to return. In addition, customer behavior is dynamic, and so table allocation should be flexible or quickly reconfigurable, to avoid delays. Restaurant table allocation could be improved if the software can be used by staff with less expertise and knowledge, and that can help the automation and optimization of the allocation process. Specially, for these reasons the idea of QPides! was proposed. This work aims to develop the backend of QPides! focusing on table allocation problem. Our proposed solution involves designing different table-allocation algorithms. These algorithms solve a constraint satisfaction problem, looking the best combination of tables at any given time that maximize the occupancy rate. The web environment used, in which the algorithms are implemented, comprises Meteor, an open-source JavaScript web application framework optimized for real-time apps, and MongoDB database. The main objective is to improve restaurants performance in terms of occupancy rate and response time. Evaluation of QPides! performance is done by applying load testing for each table allocation algorithm. All testing carried out in t

Community networks have emerged under the mottos, Community networks have emerged under the mottos “break the strings that are limiting you”, “don't buy the network, be the network” or “a free net for everyone is possible”. Such networks create a measurable social impact as they provide to the community the right and opportunity of communication. As any other network that mixes wired and wireless links, the routing protocol must face several challenges that arise from the unreliable nature of the wireless medium. Link quality tracking helps the routing layer to select links that maximize the delivery rate and minimize traffic congestion. Moreover, link quality prediction has proved to be a technique that surpasses link quality tracking by foreseeing which links are more likely to change its quality. In this work, we focus on link quality prediction by means of a time series analysis. We apply this prediction technique in the routing layer of large-scale, distributed, and decentralized networks. We demonstrate that it is possible to accurately predict the link quality in 98% of the instances, both in the short and the long terms. Particularly, we analyse the behaviour of the links globally to identify the best prediction algorithm and metric, the impact of lag windows in the results, the prediction accuracy some time steps ahead into the future, the degradation of prediction over time, and the correlation of prediction with topological features. Moreover, we also analyse the behaviour of links individually to identify the variability of link quality prediction between links, and the variability of link quality prediction over time. Finally, we also present an optimized prediction method that considers the knowledge about the expected link quality values., Peer Reviewed, Postprint (author's final draft)

This work presents a technological analysis of guifi.net, a free, neutral, and open-access community network. Guifi.net consists of more than 27,000 operational nodes, which makes it the world’s largest community network in terms of the number of nodes and coverage area. This paper describes the characteristics of the network, the link level topology, its growth over a decade, and its resilience in terms of availability and reachability of network nodes. Our study is based on open data published by guifi.net regarding its nodes and wireless links, monitoring information, community database, and its web portal. The data includes historical information that covers the lifetime of the network. The scale and diversity of the network requires a separate analysis of the subsets of the entire dataset by area or by separating the core from the leaf nodes. This shows some degree of diversity in local characteristics caused by several demographic, geographic, technological, and network design factors. We focus on the following aspects: technological network diversity, topology characteristics, evolution of the network over time, analysis of robustness, and its effect on networking service availability. In addition, we analyse how the community, the technology used, the geographical region where the network is deployed, and its self-organised structure shape the network properties and determine its strengths and weaknesses. The study demonstrates that the guifi.net community network is diverse in technological choices for hardware, link protocols, and channels and uses a combination of routing protocols yet provides a common private IP network. The graph topology follows a power- law distribution for links in regions up to a few thousand Km 2 , limited to the scope of wireless links. Network growth has two aspects: a geographic growth of the network core using long distance links with wireless or fibre, and the local growth in density with leaf low-cost leaf nodes. The resilie, Peer Reviewed, Postprint (author's final draft)

Premi extraordinari doctorat UPC curs 2015-2016, àmbit Enginyeria de les TIC, Contributory and volunteer computing ecosystems built around a community of participants need, like any other common-pool resources, an adaptive governance mechanism to guarantee the sustainability of the ecosystem. Reciprocity incentive mechanisms based on economic principles have been proved efficient solutions to regulate the resource sharing and allocation in large computing architectures, guaranteeing a direct retribution for each individual contribution even in presence of misbehaving users. However, while these mechanisms preserve the macro-equilibrium of the computational shared resources (e.g., CPU or memory), participants with fewer resources face problems competing for the attention of other members with more resources to cooperate with; making it difficult to apply such principles in practice. Additionally, active members of the community contributingin other aspects (e.g., doing administrative tasks or developing software) are not contemplated in traditional schemes although their time and effort are also part of the common-pool resource and hence, should be retributed somehow. The aim of this thesis is to revisit some of the architectural aspects of current systems and propose a framework to govern contributory and volunteer computing ecosystems in a fairer way based on principles of participatory economics. Our main contributions in this thesis are threefold. First, we examine the mechanisms ruling the resource sharing and propose a new reciprocal incentive mechanism that measures participants¿ effort on sharing resources instead of their direct contribution, so it increases the collaboration opportunities of users with fewer resources in heterogeneous scenarios. Second, we propose a regulation mechanism for allocating new computational devices and distribute new resources within them, with the objective of increasing their impact in the common-pool resources when the demand of resources is supplied by the community. Third, we propose new methods to d, Els sistemes de computació voluntària o contributiva construïts al voltant de comunitats de participants necessiten, com qualsevol altre common-pool resource, mecanismes de govern adaptatius que garanteixin la sostenibilitat de l'ecosistema. Els incentius recíprocs basats en principis econòmics han demostrat ser solucions eficients per regular la compartició i assignació de recursos en arquitectures de gran escala, garantint una retribució directa per cada contribució, inclús en presència d’usuaris maliciosos. No obstant això, mentre aquests mecanismes preserven el macro equilibri dels recursos compartits (p. ex., CPU o memòria), els participants amb menys recursos tenen problemes per competir per l'atenció dels altres membres amb més recursos quan volen cooperar amb ells; fent difícil en la pràctica aplicar aquests principis. A més a més, els membres actius de la comunitat contribuint en altres aspectes (p. ex., realitzant tasques administratives, o desenvolupant software) no es torben contemplats en els esquemes tradicions tot i que el seu temps i esforç també son part del common-pool resource i, per tant, haurien de ser compensats. L'objectiu d'aquesta tesi és revisar alguns dels aspectes d’arquitectura que fan que aquestes estratègies no funcionin i proposar un framework per governar ecosistemes de computació voluntària o contributiva duna manera més justa utilitzant principis de participació econòmica. Primer, examinem els mecanismes que controlen la compartició de recursos i proposem un nou mecanisme d’incentiu recíproc que mesura l'esforç dels participants mentre comparteixen recursos en comptes de la seva contribució directa, de manera que les oportunitats per cooperar incrementen pels usuaris amb menys recursos. En segon lloc, proposem un mecanisme per regular l'assignació de noves màquines de computació i recursos, amb l'objectiu de millorar el seu impacte en escenaris amb common-pool resource quan la demanda de recursos ha de ser subministrada col·lectiva, Award-winning, Postprint (published version)

Email Print Request Permissions Technical communities are social structures that emerge around the interest of individuals to build and deploy their own technology or communication infrastructure, such as wireless community networks. In these communities, the access to shared resources is regulated by incentive mechanisms, which are usually based on the members' contributions. Typically, technical contributions are computed by these mechanisms, ignoring the non-technical activities that members voluntarily perform to keep the community alive, e.g., administration and coordination of the tasks performed by the sub-communities. This article presents a regulation mechanism that rewards not only the contribution of shared resources to the community, but also the participation of the community members in non-technical activities. This proposal was evaluated using simulations, and the obtained results allow researchers and managers of technical communities to build appropriate incentive mechanisms that rewards both, technical and non-technical contributions of their members., Peer Reviewed, Postprint (published version)

Roles and positions are structural components in complex social systems which group actors based on how similarly they are connected to the rest of the actors. Role and position detection methods have been successfully used to evaluate and understand the dynamics of social networks and the behavior of their members. However, actor similarities used to detect positions have been based on pairwise comparisons so far: e.g., structural equivalence states that Alice and Bob are in the same position if they are both connected or not to the same other actors in the network, one by one. In this work we present a new framework to find positions and roles using comparisons between actors and sets of actors instead of just using pairwise comparisons. In this way we enable the usage of many more measures of similarity inside position and role detection methods, e.g., based on distances, community structure, triangles and cliques. As a result, we can identify new types of easily interpretable positions. Additionally, the proposed idea can be adapted to more complex models like hypergraphs or multiplex/multi-relational networks. We have evaluated our work on both synthetic and real data, using several existing and new similarity measures and providing both qualitative and quantitative evidence of the new possibilities enabled by our approach., Peer Reviewed, Postprint (published version)