Assembling thefacebook: Using heterogeneity to understand online social network assembly

Online social networks represent a popular and diverse class of social media systems. Despite this variety, each of these systems undergoes a general process of online social network assembly, which represents the complicated and heterogeneous changes that transform newly born systems into mature platforms. However, little is known about this process. For example, how much of a network's assembly is driven by simple growth? How does a network's structure change as it matures? How does network structure vary with adoption rates and user heterogeneity, and do these properties play different roles at different points in the assembly? We investigate these and other questions using a unique dataset of online connections among the roughly one million users at the first 100 colleges admitted to Facebook, captured just 20 months after its launch. We first show that different vintages and adoption rates across this population of networks reveal temporal dynamics of the assembly process, and that assembly is only loosely related to network growth. We then exploit natural experiments embedded in this dataset and complementary data obtained via Internet archaeology to show that different subnetworks matured at different rates toward similar end states. These results shed light on the processes and patterns of online social network assembly, and may facilitate more effective design for online social systems.Comment: 13 pages, 11 figures, Proceedings of the 7th Annual ACM Web Science Conference (WebSci), 201

Sob o olhar da comunidade local: mudanças ambientais na área de proteção ambiental de Anhatomirim, Sul do Brasil

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Biológicas, Programa de Pós-Graduação em Ecologia, Florianópolis, 2016.A Área de Proteção Ambiental de Anhatomirim (APAA), inserida no contexto da Baía Norte da Ilha de Santa Catarina, é uma unidade de conservação de Uso Sustentável, criada com os objetivos de proteção da população residente de Sotalia guianensis (botos-cinza), bem como a proteção de remanescentes da Floresta Ombrófila Densa e recursos hídricos de relevante interesse para a sobrevivência das comunidades de pescadores artesanais da região e suas práticas artesanais. Nos últimos 23 anos, além da tendência de alteração nos padrões de ocupação dos botos-cinza, com a diminuição da frequência de avistamentos no local considerado de maior incidência da população, a Baía dos Golfinhos, a APAA e o seu entorno vêm sofrendo um acelerado desenvolvimento urbano e intensa atividade turística, intensificando problemas ambientais, sociais e de infra-estrutura local. O conhecimento ecológico local (CEL) de moradores residentes em unidades de conservação contribui para o entendimento do contexto local, baseado em sua experiência empírica do uso de recursos naturais e status de preservação da unidade de conservação e seu entorno, convergindo para a efetividade dos objetivos estabelecidos para a área de proteção. O CEL pode auxiliar no planejamento, adaptação e mitigação de situações ambientais e sociais a que a área possa estar suscetível. Sob o enfoque da Etnoecologia, o objetivo desta pesquisa foi investigar as mudanças ambientais ocorridas e em curso na APAA, sob a perspectiva da comunidade residente, assim como identificar a distribuição espacial dos botos-cinza na Baía Norte da Ilha de Santa Catarina, a partir da percepção de pescadores locais desta Baía. Foram realizadas entrevistadas semi-estruturadas, com moradores locais e pescadores artesanais, na APAA e ao longo da Baía Norte, respectivamente. Para o primeiro artigo foram realizadas 76 entrevistas individuais com moradores da comunidade da Costeira da Armação, nas quais buscou-se investigar se há diferença na percepção sobre mudanças ambientais, entre grupos de moradores com maior ou menor relação com a unidade de conservação. A maior (G1) ou menor (G2) relação foi determinada de acordo com ofício de trabalho e/ou maior ou menor envolvimento com questões referentes à APAA, as quais poderiam aproximar tais informantes a uma maior interação e ciência nos assuntos relativos à área de proteção, assim como seus próprios interesses convergindo para tal. Todos os entrevistados perceberam mudanças ambientais na APAA e seu entorno, não havendo diferença significativa no número de citações de mudanças entre grupos. Portanto, a maior ou menor relação com a área de proteção não se mostrou como diferencial na percepção ambiental de mudanças ocorridas e em curso na APAA. Devido à sua pequena população e a economia centralizada em somente duas atividades (pesca artesanal e turismo), o conhecimento e a percepção ambiental estão distribuídos pela comunidade como um todo e a APAA é amplamente reconhecida pela comunidade residente. No segundo capítulo foram realizadas 56 entrevistas com pescadores artesanais, em sete comunidades ao longo da Baía Norte. Os entrevistados relataram que a população de botos sempre foi observada em toda Baía Norte, tanto na costa continental quanto na da Ilha de Santa Catarina. Suas áreas de maior concentração informadas foram a Baía de São Miguel e a Baía dos Golfinhos, essa última não relatada pelos pescadores locais da comunidade adjacente a ela. Foram investigadas a existência de sobreposições de áreas de pesca e áreas de deslocamento e concentração de botos, assim como a possível sobreposição de espécies-alvo da pesca e da dieta dos botos, a partir do conhecimento ecológico local dos pescadores. Os entrevistados não relataram consequências negativas para tais sobreposições. Foram citadas algumas ameaças na Baía Norte aos botos, como as redes fundeadas e as embarcações turísticas (escunas), em sua maioria, consideradas pelos colaboradores como ameaças reversíveis (fáceis de se mitigar ou fiscalizar) mas, estas não foram atestadas como as verdadeiras causas da diminuição de avistamentos de botos na Baía dos Golfinhos. A percepção ambiental e conhecimento ecológico das comunidades pesqueiras, oferecem uma rica fonte de informações que pode auxiliar a conservação e manejo de espécies, assim como a manutenção de práticas artesanais e utilização sustentável de recursos. Trazem indicativos importantes sobre a efetividade da UC, com vistas para uma gestão participativa, assim como evidenciam alguns conflitos com os órgãos fiscalizadores, mas também se certificam das ações efetivas realizadas na área de proteção para a elaboração de novas estratégias.Abstract : Anhatomirim?s Environmental Protection Area (APAA), inserted in Santa Catarina Island?s North Bay, is a Sustainable Use conservation unit, created to protect the Sotalia guianensis (Guiana dolphin) resident population, as well as remaining Dense Ombrophylous Forest and water resources of relevant interest to the survival of artisanal fishermen?s communities in the region and their artisanal practices. In the past 23 years, along with the trend of change in the occupancy patterns of Guiana dolphin there is a decreasing frequency sightings at locations considered most incident, Dolphins Bay and APAA and its surroundings are undergoing an accelerated urban development and an intensive touristic activity, intensifying the environmental, social and infrastructure problems. The resident?s local ecological knowledge (LEK) living in conservation units, contributes to the understanding, based on their empirical experience, the use of natural resources and preservation status of the conservation unit and its surroundings, converging to the effectiveness of the objectives set for the protection area. LEK can assist in planning, adaptation and mitigation of environmental and social situations which the area may be susceptible. Focused on ethnoecology, the objectives of this research were to investigate and evaluate the occurred and ongoing environmental changes in APAA, from the community perspective, as well as understand the decreasing frequency of sightings of Sotalia guianensis, from local fishers perception of Santa Catarina Island?s North Bay. Semi-structured interviews were conducted with residents and artisanal fishers, at APAA and along the North Bay, respectively. In the first article, 76 individual interviews were conducted, and we investigated if there we are differences between groups of residents with higher or lower relation with the protected area. Higher (G1) or lower (G2) groups of relation were determined according to the conomic activity and/or more or less involvement with APAA?s issues, which could approach such collaborators to an increased interaction and awareness about the protectied area, as well as their own interests converging for this. All interviewees noticed environmental changes in APAA and its surroundings, with no significant difference in the number of citations of changes among the groups. Therefore, the higher or lower relation with the protection area was not differential in occurred and ongoing environmental changes perception at APAA. Due to its small population and centralized economic practice in only two activities (artisanal fishing and tourism), knowledge and environmental awareness are entirely distributed through the community and APAA is widely recognized by resident community. In the second article, 56 interviews were conducted with artisanal fishers, in seven communities throughout North Bay. Interviewees reported that porpoises population was always observed throughout North Bay, both on mainland coast and in Santa Catarina Island, and its highest concentration reported areas were São Miguel Bay and Dolphin Bay, the latter not reported by local fishers adjacent to it. Possible overlapping of fishing areas and porpoise?s areas of displacement and concentration were investigated, as well as overlap of fishing target species and species on porpoises? diet, from fishers ecological knowledge, in which interviewees reported no negative evidence for such overlapping. Some threats to porpoises were cited in North Bay, as bottom-set gillnets and schooners, mostly considered as reversible threats (easy to mitigate or supervise), but these are not attested as the true causes of porpoise?s sightings decrease in Dolphins Bay. Fishing communities? environmental perceptions and ecological knowledge offers a rich source of specific information that can help conservation and management of species, as well as maintenance of handcraft practices and sustainable use of resources. They bring important indications about protected area effectiveness, aiming a participative management, as well as show some conflicts with surveillance body, but also make sure the effective actions taken in protection area for new development strategies

FROM SMALL-WORLDS TO BIG DATA:TEMPORAL AND MULTIDIMENSIONAL ASPECTS OF HUMAN NETWORKS

In this thesis we address the close interplay among mobility, offline relationships and online interactions and the related human networks at different dimensional scales and temporal granularities. By generally adopting a data-driven approach, we move from small datasets about physical interactions mediated by human-carried devices, describing small social realities, to large-scale graphs that evolve over time, as well as from human mobility trajectories to face-to-face contacts occurring in different geographical contexts. We explore in depth the relation between human mobility and the social structure induced by the overlapping of different people's trajectories on GPS traces collected in urban and metropolitan areas. We define the notions of geo-location and geo-community which are operational in describing in a unique framework both spatial and social aspects of human behavior. Through the concept of geo-community we model the human mobility adopting a bipartite graph. Thanks to this graph representation we can generate a social structure that is plausible w.r.t. the real interactions. In general the modeling approach have the merit for reporting the mobility in a graph-theoretic framework making the study of the interplay mobility/sociality more affordable and intuitive. Our modeling approach also results in a mobility model, Geo-CoMM, which lies on and exploits the idea of geo-community. The model represents a particular instance of a general framework we provide. A framework where the social structure behind the preferred-location based mobility models emerges. We validate Geo-CoMM on spatial, temporal, pairwise connectivity and social features showing that it reproduces the main statistical properties observed in real traces. As concerns the offline/online interplay we provide a complete overview of the close connection between online and offline sociality. To reach our goal we gather data about offline contacts and social interactions on Facebook of a group of students and we propose a multidimensional network analysis which allows us to deeply understand how the characteristics of users in the distinct networks impact each other. Results show how offline and Facebook friends are different. This way we confirm and worsen the general intuition that online social networks have shifted away from their original goal to mirror the offline sociality of individuals. As for the role and the social importance, it becomes apparent that social features such as user popularity or community structure do not transfer along social dimensions, as confirmed by our correlation analysis of the network layers and by the comparison among the communities. In the last chapters we analyze the evolution of the online social network from a physical time perspective, i.e. considering the graph evolution as a graph time-series and not as a function of the network basic properties (number of nodes or links). As for the physical time in a user-centric viewpoint, we investigate the bursty nature of the link creation process in online social network. We prove not only that it is a highly inhomogeneous process, but also identify patterns of burstiness common to all nodes. Then we focus on the dynamic formation of two fundamental network building components: dyads and triads. We propose two new metrics to aid the temporal analysis on physical time: link creation delay and triangle closure delay. These two metrics enable us to study the dynamic creation of dyads and triads, and to highlight network behavior that would otherwise remain hidden. In our analysis, we find that link delays are generally very low in absolute time and are largely independent of the dates people join the network. To highlight the social nature of this metric, we introduce the term \textit{peerness} to quantify how well linked users overlap in lifetimes. As for triadic closure delay we first introduce an algorithm to extract of temporal triangle which enables us to monitor the triangle formation process, and to detect sudden changes in the triangle formation behavior, possibly related to external events. In particular, we show that the introduction of new service functionalities had a disruptive impact on the triangle creation process in the network

Predicting encounter and colocation events

Although an extensive literature has been devoted to mine and model mobility features, forecasting where, when and whom people will encounter/colocate still deserve further research effort s. Forecasting people\u2019s encounter and colocation features is the key point for the success of many applications rang- ing from epidemiology to the design of new networking paradigms and services such as delay tolerant and opportunistic networks. While many algorithms which rely on both mobility and social informa- tion have been proposed, we propose a novel encounter and colocation predictive model which predicts user\u2019s encounter and colocation events and their features by exploiting the spatio-temporal regularity in the history of these events. We adopt a weighted features Bayesian predictor and evaluate its accuracy on two large scales WiFi and cellular datasets. Results show that our approach could improve prediction accuracy with respect to standard na\uefve Bayesian and some of the state of the art predictors

Evolution of Ego-networks in Social Media with Link Recommendations

Ego-networks are fundamental structures in social graphs, yet the process of their evolution is still widely unexplored. In an online context, a key question is how link recommender systems may skew the growth of these networks, possibly restraining diversity. To shed light on this matter, we analyze the complete temporal evolution of 170M ego-networks extracted from Flickr and Tumblr, comparing links that are created spontaneously with those that have been algorithmically recommended. We find that the evolution of ego-networks is bursty, community-driven, and characterized by subsequent phases of explosive diameter increase, slight shrinking, and stabilization. Recommendations favor popular and well-connected nodes, limiting the diameter expansion. With a matching experiment aimed at detecting causal relationships from observational data, we find that the bias introduced by the recommendations fosters global diversity in the process of neighbor selection. Last, with two link prediction experiments, we show how insights from our analysis can be used to improve the effectiveness of social recommender systems.Comment: Proceedings of the 10th ACM International Conference on Web Search and Data Mining (WSDM 2017), Cambridge, UK. 10 pages, 16 figures, 1 tabl

Mastodon Content Warnings: Inappropriate Contents in a Microblogging Platform

Our social communications and the expression of our beliefs and thoughts are becoming increasingly mediated and diffused by online social media. Beyond countless other advantages, this democratization and freedom of expression is also entailing the transfer of unpleasant offline behaviors to the online life, such as cyberbullying, sexting, hate speech and, in general, any behavior not suitable for the online community people belong to. To mitigate or even remove these threats from their platforms, most of the social media providers are implementing solutions for the automatic detection and filtering of such inappropriate contents. However, the data they use to train their tools are not publicly available. In this context, we release a dataset gathered from Mastodon, a distribute online social network which is formed by communities that impose the rules of publication, and which allows its users to mark their posts inappropriate if they perceived them not suitable for the community they belong to. The dataset consists of all the posts with public visibility published by users hosted on servers which support the English language. These data have been collected by implementing an ad-hoc tool for downloading the public timelines of the servers, namely instances, that form the Mastodon platform, along with the meta-data associated to them. The overall corpus contains over 5 million posts, spanning the entire life of Mastodon. We associate to each post a label indicating whether or not its content is inappropriate, as perceived by the user who wrote it. Moreover, we also provide the full description of each instance. Finally, we present some basic statistics about the production of inappropriate posts and the characteristics of their associated textual content

Public discourse and news consumption on online social media: A quantitative, cross-platform analysis of the Italian Referendum

The rising attention to the spreading of fake news and unsubstantiated rumors on online social media and the pivotal role played by confirmation bias led researchers to investigate different aspects of the phenomenon. Experimental evidence showed that confirmatory information gets accepted even if containing deliberately false claims while dissenting information is mainly ignored or might even increase group polarization. It seems reasonable that, to address misinformation problem properly, we have to understand the main determinants behind content consumption and the emergence of narratives on online social media. In this paper we address such a challenge by focusing on the discussion around the Italian Constitutional Referendum by conducting a quantitative, cross-platform analysis on both Facebook public pages and Twitter accounts. We observe the spontaneous emergence of well-separated communities on both platforms. Such a segregation is completely spontaneous, since no categorization of contents was performed a priori. By exploring the dynamics behind the discussion, we find that users tend to restrict their attention to a specific set of Facebook pages/Twitter accounts. Finally, taking advantage of automatic topic extraction and sentiment analysis techniques, we are able to identify the most controversial topics inside and across both platforms. We measure the distance between how a certain topic is presented in the posts/tweets and the related emotional response of users. Our results provide interesting insights for the understanding of the evolution of the core narratives behind different echo chambers and for the early detection of massive viral phenomena around false claims

A study on iron-chalcogenides superconductors: from samples preparation to physical properties

2014 - 2015In the scientific community there is a great interest to explore new superconducting materials suitable for high field applications in order to meet the needs of industrial claims. In this framework, newly discovered Fe-Based Superconductors (IBSC) are a promising choice, especially due to their critical temperature intermediate between low and high Tc materials, as well as an extremely high upper critical field. The aim of this work has been the preparation and the study of physical properties of iron-chalcogenides superconducting samples, in particular polycrystalline FeSe and FeSeTe. The iron-chalcogenides family has been choosen mostly because of its interesting superconducting properties and also due to its simple crystalline structure and to the lack of poisonous elements in its composition. Opening a completely new research field at the ENEA CR Frascati, several routes of samples production have been carried out. I achieved part of the necessary know-how working also in other laboratories that have great experience on iron-based superconductors preparation, in particular the National Institute for Materials Science (NIMS) laboratories of Tsukuba in Japan, where I worked at the Nano Frontier Materials Group, under the leadership of Prof. Dr. Takano. I also had the chance to spend a brief period at the laboratories of CNR SPIN Genova and the Physics and Chemistry Departments at University of Genova, where I could meet researchers skilled in the production of iron-based samples. Most of the know-how was achieved by direct experience. Even if some of the routes for samples preparation did not brought to the expected results, some of these techniques gave interesting results, other routes deserve further optimization. Concerning the FeSe compound, two preparation processes have been implemented: the electrochemical deposition on iron substrate, and the solid state reactive synthesis. The former gave FeSe thin films containing the right tetragonal -phase, but the optimization of the superconducting properties in these samples would be very challenging and time-consuming. The solid state reactive sintering lead to the preparation of superconducting samples with good Tc onset but containing several impurities, which compromised the steepness of transition and the current carrying capability. This route requires further optimization, which can be achieved keeping cleaner all the process steps. Three routes were implemented for the preparation of FeSeTe samples, the solid state reactive synthesis, the mechano-chemical synthesis and the synthesis by fusion. The first two routes, as happened for FeSe samples, need further optimization. The third route brought to the preparation of several very good polycrystalline samples by a melting process, with heat treatment (HT) at temperatures of about 970 °C followed by cooldown to about 400 °C. It was verified that, as a consequence of the fusion process, impurities and spurious phases between grains are mostly removed, a preferential orientation of the samples is promoted and the critical current is enhanced. Therefore this fabrication route is recommended in view of applications, even if further efforts are needed to develop the material ready to use for example as a target for films deposition or eventually for the preparation of actual strands. In this work the main physical characterizations performed on all kinds of produced samples are shown. The reproducibility of the superconducting properties of samples prepared with the same procedure has been verified and only the representative samples for each group have been shown for clarity and readability. In particular the performing samples have been object of an extensive characterization, carried out in different superconducting labs at ENEA CR Frascati, at Master lab of CNR-SPIN Salerno and Physics Department of University of Salerno. Beside structural, magnetic, transport and calorimetric measurements, several analysis concerning the pinning mechanisms acting and competing inside the produced samples have been performed, within the framework of several literature models. As expected, pinning properties strongly depend on the preparation procedures which induces the defect structure into the samples. Magnetic relaxation measurements have supported this analysis, giving a corroborating possible interpretation of the measured peak effect, if present, and to the behaviour of the effective energy barrier as a function of the current density. In conclusion, despite the undeniable polycrystalline nature of the FeSeTe samples, those obtained by melting process present superconducting properties closely resembling the single crystals ones, with onset temperatures of about 15 K and quite steep transitions. Best performing samples have large hysteresis cycles well opened up to 12 T (at about 9 K) and up to 18 T (at about 7 K) with a robust critical current density weakly dependent on the applied field in the high field range. [edited by author]Nella comunità scientifica c’è grande interesse per quanto riguarda l’esplorazione di nuovi materiali superconduttori adatti per applicazioni ad alto campo, con l’obiettivo di venire incontro alle incalzanti necessità dell’industria. In questo contesto, i materiali superconduttori a base di ferro, scoperti recentemente, rappresentano un’opzione promettente, soprattutto grazie alla loro temperatura critica, intermedia rispetto a quelle dei superconduttori a bassa e ad alta Tc, e anche grazie ai loro campi magnetici superiori estremamente alti. L’obiettivo di questo lavoro è stata la preparazione e lo studio delle proprietà fisiche di campioni superconduttori di a base di ferro-calcogenuri, in particolare di FeSe e FeSeTe policristallino. La famiglia dei ferro-calcogenuri è stata scelta soprattutto a causa delle sue interessanti proprietà superconduttive, e anche a causa della sua semplice struttura cristallina e alla mancanza di elementi tossici nella sua composizione. Ho portato avanti diverse strade per la produzione dei campioni, aprendo così un campo di ricerca completamente nuovo all’ENEA di Frascati. Ho conseguito parte delle competenze necessarie per questo lavoro lavorando anche presso altri laboratori che vantano grande esperienza nella preparazione di materiali superconduttori a base di ferro, in particolare presso i laboratori del National Institute of Material Science (NIMS) di Tsukuba in Giappone, dove ho lavorato presso il Nano Frontier Material Group, guidato dal Prof. Dr. Takano. Ho avuto anche l’opportunità di lavorare un breve periodo presso i laboratori del CNR SPIN di Genova e presso i dipartimenti di Fisica e Chimica dell’Università di Genova, dove ho potuto confrontarmi con ricercatori esperti nella produzione di campioni superconduttori a base di ferro. La maggior parte delle competenze le ho comunque acquisite per esperienza diretta. Anche se alcune delle strade intraprese per la preparazione dei campioni non hanno portato ai risultati sperati, alcune di queste tecniche hanno dato risultati interessanti, altre meritano senz’altro un ulteriore ottimizzazione. Per quanto riguarda i campioni in FeSe, sono stati implementati due processi per la preparazione: la deposizione elettrochimica su substrato di ferro e la sintesi allo stato solido. Il primo processo ha portato come risultato film sottili di FeSe contenenti la fase tetragonale superconduttiva, ma l’ottimizzazione delle proprietà superconduttive di questi campioni sarebbe un procedimento molto lungo e complesso. La sintesi allo stato solido ha portato alla preparazione di campioni superconduttivi con una buona Tc di onset ma contenenti molte impurezze, che hanno compromesso la ripidità della transizione e le proprietà di trasporto di corrente. Questa tecnica di preparazione richiede un’ottimizzazione futura, che potrà essere ottenuta mantenendo più pulite tutte le fasi del processo. Per la preparazione del FeSeTe sono state utilizzate tre tecniche, la sintesi allo stato solido, la sintesi meccano-chimica e la sintesi per fusione. Le prime due strade, come visto per i campioni in FeSe, hanno bisogno di essere ulteriormente ottimizzate. La terza strada ha portato alla preparazione di diversi campioni policristallini di qualità molto buona tramite un processo di fusione, con trattamenti termici a temperature di circa 970°C seguiti dl raffreddamenti a circa 400°C. È stato verificato che, come conseguenza del processo di fusione, le impurità e le fasi spurie tra i grani sono quasi totalmente rimosse, è promosso l’orientamento preferenziale dei campioni e la corrente critica risulta migliorata. Quindi questa tecnica per la preparazione dei campioni è quella raccomandata in vista delle applicazioni, anche se ulteriori sforzi saranno necessari per sviluppare un materiale pronto per l’uso ad esempio come target per la deposizione di film o eventualmente per la preparazione di veri e propri fili. In questo lavoro di tesi sono state mostrate le principali caratterizzazioni eseguite su tutti i tipi di campioni prodotti. La riproducibilità delle proprietà superconduttive dei campioni preparati con le stesse procedure è stata verificata e solo i campioni rappresentativi per ogni gruppo sono stati mostrati, per chiarezza e per non compromettere la leggibilità della tesi. In particolare i campioni migliori sono stati oggetto di una caratterizzazione estesa, portata avanti in vari laboratori di superconduttività, all’ENEA di Frascati, al Master Lab del CNR SPIN di Salerno e al dipartimento di Fisica dell’Università di Salerno. Oltre alle caratterizzazioni strutturali, magnetiche, di trasporto e calorimetriche, sono state portate avanti diverse analisi riguardanti i meccanismi di pinning che agiscono e competono all’interno dei campioni prodotti, nell’ambito di diversi modelli tratti dalla letteratura scientifica relativa all’argomento. Come previsto, le proprietà di pinning dipendono fortemente dalle procedure di preparazione che inducono e influenzano la struttura dei difetti all’interno dei campioni. Queste analisi sono state supportate anche da misure di rilassamento magnetico, che hanno corroborato l’interpretazione del peak effect, quando presente, e il comportamento dell’energia di attivazione di barriera in funzione della densità di corrente. In conclusione, nonostante l’innegabile natura policristallina dei campioni di FeSeTe preparati, quelli ottenuti per fusione presentano proprietà superconduttive che ricordano da vicino quelle dei campioni cristallini, con temperature di onset di circa 15 K e transizioni piuttosto strette. I campioni migliori hanno infatti cicli di isteresi ben aperti fino a 12 T (a circa 9 K) e fino a 18 K (a circa 7 K) con una densità di corrente critica che dipende debolmente dal campo magnetico nell’intervallo degli alti campi. [a cura dell'autore]XIV n.s

Planejamento tributário na distribuição de juros sobre o capital próprio versus dividendos : uma proposta da melhor opção de remuneração do capital para empresas optantes pelo lucro real

Orientador: Blenio Cesar Severo PeixeMonografia (Especialização) - Universidade Federal do Paraná, Setor de Ciências Sociais Aplicadas, Curso de Especialização em Auditoria IntegralResumo: O bom desempenho financeiro da instituição esta diretamente ligado ao planejamento tributário adotado, e este, certamente deverá analisar a política de distribuição de dividendos ou o pagamento de juros sobre o capital próprio, pois terão reflexos diretos no preço das ações da Companhia. Desta forma, faz-se necessária um estudo comparativo entre as duas opções para obter o caminho para a maior economia tributária, sem com isso descapitalizá-la. Embora seja um assunto polêmico, o planejamento é de suma importância para a boa gestão tributária e deve ser levado em conta o fato de que em determinado período a empresa poderá ter resultados ruins, porém se dispuser de recursos financeiros, poderá garantir uma melhor remuneração aos seus acionistas. Os juros sobre o capital próprio, uma inovação brasileira, foi introduzido através da Lei n° 9.249/95 e permitiu que as despesas com juros sobre o capital próprio pudessem ser dedutíveis para apuração do Lucro Real e da base de cálculo da Contribuição Social. Observando regras específicas e o princípio da não cumulatividade, a empresa fara retenção de 15% para lmposto de Renda sobre o rendimento pago a pessoa física do sócio, porém terá sua base de cálculo reduzida para a apuração do Lucro Real, onde incidiria 15% mais adicional de 1 0% caso fosse adotada a distribuição de Lucro. E ainda, quando o rendimento se referir a remuneração de sócios pelo trabalho na empresa, não haverá incidência dos encargos da Previdência Social. Porém, mais relevante do que a substituição dos dividendos ou do pagamento da remuneração dos sócios que trabalham na empresa pelos juros sobre o capital próprio e a economia tributária produzida e a minimização do impacto causado pelo desembolso de caixa, não deixando a Companhia vulnerável ou impossibilitada de fazer investimentos e gerar mais riquezas aos próprios acionista

On the properties of human mobility

The current age of increased people mobility calls for a better understanding of how people move: how many places does an individual commonly visit, what are the semantics of these places, and how do people get from one place to another. We show that the number of places visited by each person (Points of Interest - PoIs) is regulated by some properties that are statistically similar among individuals. Subsequently, we present a PoIs classification in terms of their relevance on a per-user basis. In addition to the PoIs relevance, we also investigate the variables that describe the travel rules among PoIs in particular, the spatial and temporal distance. As regards the latter, existing works on mobility are mainly based on spatial distance. Here we argue, rather, that for human mobility the temporal distance and the PoIs relevance are the major driving factors. Moreover, we study the semantic of PoIs. This is useful for deriving statistics on people's habits without breaking their privacy. With the support of different datasets, our paper provides an in-depth analysis of PoIs distribution and semantics; it also shows that our results hold independently of the nature of the dataset in use. We illustrate that our approach is able to effectively extract a rich set of features describing human mobility and we argue that this can be seminal to novel mobility research