A class of cubic Rauzy Fractals

In this paper, we study arithmetical and topological properties for a class of Rauzy fractals ${\mathcal R}_a$ given by the polynomial $x^3- ax^2+x-1$ where $a \geq 2$ is an integer. In particular, we prove the number of neighbors of ${\mathcal R}_a$ in the periodic tiling is equal to $8$. We also give explicitly an automaton that generates the boundary of ${\mathcal R}_a$. As a consequence, we prove that ${\mathcal R}_2$ is homeomorphic to a topological disk

Melnikov analysis in nonsmooth differential systems with nonlinear switching manifold

We study the family of piecewise linear differential systems in the plane with two pieces separated by a cubic curve. Our main result is that 7 is a lower bound for the Hilbert number of this family. In order to get our main result, we develop the Melnikov functions for a class of nonsmooth differential systems, which generalizes, up to order 2, some previous results in the literature. Whereas the first order Melnikov function for the nonsmooth case remains the same as for the smooth one (i.e. the first order averaged function) the second order Melnikov function for the nonsmooth case is different from the smooth one (i.e. the second order averaged function). We show that, in this case, a new term depending on the jump of discontinuity and on the geometry of the switching manifold is added to the second order averaged function

Serial Activists: Political Twitter Beyond Influentials and the Twittertariat

This paper introduces a group of politically-charged Twitter users that deviates from elite and ordinary users. After mining 20M tweets related to nearly 200 instances of political protest from 2009 to 2013, we identified a network of individuals tweeting across geographically distant protest hashtags and revisited the term serial activists. We contacted 191 individuals and conducted 21 in-depth, semi-structured interviews thematically-coded to provide a typology of serial activists and their struggles with institutionalized power. We found that these users have an ordinary following, but bridge disparate language communities and facilitate collective action by virtue of their dedication to multiple causes. Serial activists differ from influentials or traditional grassroots activists and their activity challenges Twitter scholarship foregrounding the two-step flow model of communication. The results add a much needed depth to the prevalent data-driven treatment of political Twitter by describing a class of extraordinarily prolific users beyond influentials and the twittertariat

Aprendizagem de cuidados complexos: um desafio no caminho da parentalidade

INTRODUÇÃO: Os pais são maioritáriamente as pessoas que prestam cuidados aos filhos. A transição para a parentalidade autónoma implica, nalgumas situações, a aquisição de competências ao nível da prestação de cuidados complexos. Este ensino, treino e demonstração são praticados durante o internamento das crianças com o objectivo de promover a autonomia familia

The Public Accountability of Social Platforms: Lessons from a Study on Bots and Trolls in the Brexit Campaign

In this article we review our study of 13,493 bot-like Twitter accounts that tweeted the U.K. European Union membership referendum and disappeared from the platform after the ballot. We discuss the methodological challenges and lessons learned from a study that emerged in a period of increasing weaponization of social media and mounting concerns about information warfare. We address the challenges and shortcomings involved in bot detection, the extent to which disinformation campaigns on social media are effective, valid metrics for user exposure, activation, and engagement in the context of disinformation campaigns, unsupervised and supervised posting protocols, along with infrastructure and ethical issues associated with social sciences research based on large-scale social media data. We argue for improving researchers’ access to data associated with contentious issues and suggest that social media platforms should offer public Application Programming Interfaces to allow researchers access to content generated on their networks. We conclude with reflections on the relevance of this research agenda to public policy

Being a Serial Transnational Activist

Transnational activism endures as a political practice turning a mirror onto the world's powerbrokers. We analyse a variety of transnational activism best characterized as serial by virtue of an observed systematic time and border-spanning commitment to protest communication. Following statistical disambiguation of a dataset of 2.5 million unique Twitter users, we identified a subset of exceptionally prolific communicators and interviewed 21 of them. We show that a noted prominence in networked communication of otherwise unremarkable Twitter users may be an upshot of purposive strategies intended to publicize, support or help orchestrate collective action. Accordingly, we propose the term “engagement compass” to address the relationship between activists' life-patterns and their personal investment in protest over time

Produção de mudas de goiabeira.

A goiaba ocupa lugar de destaque dentre as frutas tropicais brasileiras. No Vale do São Francisco, a área plantada com a cultura é de 5.000 hectares, distribuídos entre os estados de Pernambuco e Bahia. A goiaba é uma ótima opção para a diversificação, entretanto, com os problemas surgidos por causa do nematoide, muitos pomares foram erradicados. Visando contribuir para a redução desses problemas, deve-se dar importância especial à produção de mudas livres de nematoides, pois, é no preparo delas que grande parte das áreas são contaminadas por essa praga. A produção de mudas é uma das etapas fundamentais no processo de implantação de um pomar e pode ser determinante para o sucesso da cultura a ser implantada. As técnicas de produção devem atender às necessidades do produtor, levando-se em consideração a disponibilidade e a localização de áreas, o grau de tecnologia e os recursos financeiros disponíveis.bitstream/item/54791/1/COT148.pd