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

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

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

Biorreatores: aspectos gerais e sua utilização para cultura de tecidos vegetais.

Cultura de Tecidos Vegetais; Biorreatores na cultura de tecidos vegetais; Vantagens do uso de biorreatores em relação ao processo de micropropagação convencional; Problemas no uso de biorreatores e como contorná-los; Principais tipos de biorreatores; Principais parâmetros físicoquímicos em um biorreator; Formas e efeitos da agitação; Formas de transferência e efeitos do oxigênio dissolvido; Efeitos provocados pelas variações de CO2 e pH.bitstream/CPATSA-2009-09/40172/1/SDC214.pd

The Geographic Embedding of Online Echo Chambers: Evidence from the Brexit Campaign

This study explores the geographic dependencies of echo-chamber communication on Twitter during the Brexit campaign. We review the evidence positing that online interactions lead to filter bubbles to test whether echo chambers are restricted to online patterns of interaction or are associated with physical, in-person interaction. We identify the location of users, estimate their partisan affiliation, and finally calculate the distance between sender and receiver of @-mentions and retweets. We show that polarized online echo-chambers map onto geographically situated social networks. More specifically, our results reveal that echo chambers in the Leave campaign are associated with geographic proximity and that the reverse relationship holds true for the Remain campaign. The study concludes with a discussion of primary and secondary effects arising from the interaction between existing physical ties and online interactions and argues that the collapsing of distances brought by internet technologies may foreground the role of geography within one’s social network

Contribuição ao conhecimento da temperatura do solo na região de Belém.

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