Fractal escapes in Newtonian and relativistic multipole gravitational fields

We study the planar motion of test particles in gravitational fields produced by an external material halo, of the type found in many astrophysical systems, such as elliptical galaxies and globular clusters. Both the Newtonian and the general-relativistic dynamics are examined, and in the relativistic case the dynamics of both massive and massless particles are investigated. The halo field is given in general by a multipole expansion; we restrict ourselves to multipole fields of pure order, whose Newtonian potentials are homogeneous polynomials in cartesian coordinates. A pure (n)-pole field has (n) different escapes, one of which is chosen by the particle according to its initial conditions. We find that the escape has a fractal dependency on the initial conditions for (n>2) both in the Newtonian and the relativistic cases for massive test particles, but with important differences between them. The relativistic motion of massless particles, however, was found to be regular for all the fields we could study. The box-counting dimension was used in each case to quantify the sensitivity to initial conditions which arises from the fractality of the escape route.Comment: 17 pages, 7 figures, uses REVTE

Cooperative response and clustering : Consequences of membrane-mediated interactions among mechanosensitive channels

Peer reviewedPublisher PD

Cato in Libya (Lucan 9)

Após a derrota e o assassinato de Pompeu, Catão tenta reorganizar as forças republicanas no Norte da África. Sua luta é política e filosófica. Lucano apresenta esse desafio através dos discursos de Catão e seus interlocutores, bem como através de uma fantástica travessia do deserto líbio. Este trabalho procura mostrar como a forma da narrativa expõe os dilemas das personagens e do próprio narrador diante da crise representada por esse momento. Estudaremos sobretudo a ordenação dos conteúdos, as intervenções do narrador, o emprego das falas em discurso direto e a manipulação da geografia africana.After Pompey’s defeat at Pharsalus and his assassination in Egypt, Cato tries to reorganise the republican forces in North Africa. His fight is a political and philosophical one. Lucan presents this challenge by means of a fantastic crossing of the Libyan desert as well as through speeches by Cato and his interlocutors. This paper attempts to show how the shape of the narrative exposes the dilemmas faced by the characters and the narrator himself in this context of crisis. I shall address the order  of the contents in book 9, the narrator’s interventions, the use of direct speech and the manipulation of African geography

Escape from attracting sets in randomly perturbed systems

The dynamics of escape from an attractive state due to random perturbations is of central interest to many areas in science. Previous studies of escape in chaotic systems have rather focused on the case of unbounded noise, usually assumed to have Gaussian distribution. In this paper, we address the problem of escape induced by bounded noise. We show that the dynamics of escape from an attractor's basin is equivalent to that of a closed system with an appropriately chosen "hole". Using this equivalence, we show that there is a minimum noise amplitude above which escape takes place, and we derive analytical expressions for the scaling of the escape rate with noise amplitude near the escape transition. We verify our analytical predictions through numerical simulations of a two-dimensional map with noise.Comment: up to date with published versio

Signatures of fractal clustering of aerosols advected under gravity

Aerosols under chaotic advection often approach a strange attractor. They move chaotically on this fractal set but, in the presence of gravity, they have a net vertical motion downwards. In practical situations, observational data may be available only at a given level, for example at the ground level. We uncover two fractal signatures of chaotic advection of aerosols under the action of gravity. Each one enables the computation of the fractal dimension $D_{0}$ of the strange attractor governing the advection dynamics from data obtained solely at a given level. We illustrate our theoretical findings with a numerical experiment and discuss their possible relevance to meteorology.Comment: Accepted for publication in Phys. Rev. E (Rapid Communications

Integrated stress response of Escherichia coli to methylglyoxal : transcriptional readthrough from the nemRA operon enhances protection through increased expression of glyoxalase I

© 2013 The Authors. Molecular Microbiology published by John Wiley & Sons Ltd.Peer reviewedPublisher PD

Collective response of self-organized clusters of mechanosensitive channels

Peer reviewedPublisher PD

O movimento operário russo e suas revoluções: a estratégia de 1905 e 1917

Apresentamos um breve ensaio sobre a organização do movimento operário russo no período 1905-1917. Em 1905 as mobilizações dos operários russos, lutando por melhores condições de vida e trabalho, avançaram para a formação dos Sovietes (conselhos operários). Na revolução de 1917 os sovietes ressurgiram com mais força, estabelecendo duplo poder na Rússia, dualidade esta que se estende até 25 de outubro de 1917, data que marca o inicio da implantação do governo soviético

Crise da acumulação, Estado e classes sociais

We discussed the structural crisis of capital accumulation that has been going on since the 1970s as a "long crisis" that we have experienced until the present moment. This was deepened by a new stage of the accumulation crisis that started in 2008 and which was aggravated by the pandemic of 2020. Finally, we approach the emergence of the covid-19 pandemic within the framework of large-scale industrial production considering the impacts that such production unleashes on the environment and other forms of life.Discutimos la crise estructural de acumulación de capital que viene ocurriendo desde la década de 1970 como una "crise larga" que hemos vivido hasta el momento actual. Esta se profundizó por cuenta una nueva etapa de la crise de acumulación que comenzó en 2008 y se vio agravada por la pandemia de 2020. Finalmente, abordamos el surgimiento de la pandemia del covid-19 en el marco de la producción industrial en gran escala, considerando los impactos que dicha producción desencadena en el medio ambiente y otras formas de vida.O objetivo do artigo é discutir a crise estrutural de acumulação do capital que se estende desde a década de 1970 como uma "longa crise" que dura até o presente momento. Esta foi aprofundada por uma nova etapa da crise de acumulação iniciada em 2008 e agravada pela pandemia de 2020. Por fim abordamos o surgimento da pandemia do covid-19 no marco da produção industrial em larga escala, considerando os impactos que tal produção desencadeia sobre o meio ambiente e outras formas de vida