Polytropic equation of state and primordial quantum fluctuations

We study the primordial Universe in a cosmological model where inflation is driven by a fluid with a polytropic equation of state $p = \alpha\rho + k\rho^{1 + 1/n}$. We calculate the dynamics of the scalar factor and build a Universe with constant density at the origin. We also find the equivalent scalar field that could create such equation of state and calculate the corresponding slow-roll parameters. We calculate the scalar perturbations, the scalar power spectrum and the spectral index.Comment: 16 pages, 4 figure

The compound Poisson limit ruling periodic extreme behaviour of non-uniformly hyperbolic dynamics

We prove that the distributional limit of the normalised number of returns to small neighbourhoods of periodic points of non-uniformly hyperbolic dynamical systems is compound Poisson. The returns to small balls around a fixed point in the phase space correspond to the occurrence of rare events, or exceedances of high thresholds, so that there is a connection between the laws of Return Times Statistics and Extreme Value Laws. The fact that the fixed point in the phase space is a repelling periodic point implies that there is a tendency for the exceedances to appear in clusters whose average sizes is given by the Extremal Index, which depends on the expansion of the system at the periodic point. We recall that for generic points, the exceedances, in the limit, are singular and occur at Poisson times. However, around periodic points, the picture is different: the respective point processes of exceedances converge to a compound Poisson process, so instead of single exceedances, we have entire clusters of exceedances occurring at Poisson times with a geometric distribution ruling its multiplicity. The systems to which our results apply include: general piecewise expanding maps of the interval (Rychlik maps), maps with indifferent fixed points (Manneville-Pomeau maps) and Benedicks-Carleson quadratic maps.Comment: To appear in Communications in Mathematical Physic

Cenarizações dos Processos de Reintegração Familiar: Compondo Redes de Cuidado e Afeto

O que se passa nos Processos de Reintegração Familiar nos Serviços de Acolhimento Institucional para Crianças e Adolescentes? Como tais processos acontecem no Município de Vitória/ES? Estas foram as perguntas que nos mobilizaram e nos lançaram ao campo de pesquisa-intervenção. Para tanto, convocamos intercessores e seus aportes teóricometodológicos: Vinciane Despret, Bruno Latour, Maturana e Varela, Deleuze, Márcia Moraes, Virginia Kastrup (entre outros) e as trabalhadoras Psicólogas e Assistentes Sociais que atuam nos serviços de acolhimento. Entendemos que as trabalhadoras são atoras que, em sua atuação cotidiana, tecem redes nas práticas da Assistência Social. As atoras de duas Casas de Acolhimento de Crianças e Adolescentes em Medida Protetiva do Município de Vitória foram participantes do exercício de PesquisarCOM, que se materializou no registro dos acontecimentos da e na rede no diário de campo coletivo, no qual compareceram inúmeras e distintas vozes. As redes tecidas pelas práticas da Assistência Social fabricam mundos, atualizando práticas e discursos historicamente constituídos e mobilizando afetos capazes de produzirem novos modos de agir e pensar. Os afetos, assim, são os motores para as possibilidades infindas da vida de reinventar-se, o que nos coloca um compromisso éticopolítico do cuidado e do acolhimento dos diversos modos da vida expressar-se. Compreendemos que a reinserção familiar começa nas primeiras intervenções com a família e que é sustentada por um olhar e um corpo sensíveis que se permitem afetar e ser afetados nos encontros. Acompanhar a tessitura de redes de cuidado e afeto, conferindo visibilidade à rede por meio de cenarizações-acontecimentos, nos favoreceu romper com uma lógica de atenção centrada na tutela e culpabilização das famílias pobres, desnaturalizando, dessa forma,verdades cristalizadas. Experimentar novas perspectivas de cuidado que emergem em ato,ampliando olhares e sensibilidades, foi a aposta que movimentou esta dissertação. Umacrença na potência da vida. Palavras-chave: Reintegração familiar; Acolhimento Institucional para Crianças e Adolescentes; PesquisarCOM; Rede

Electrical current-driven pinhole formation and insulator-metal transition in tunnel junctions

Current Induced Resistance Switching (CIS) was recently observed in thin tunnel junctions (TJs) with ferromagnetic (FM) electrodes and attributed to electromigration of metallic atoms in nanoconstrictions in the insulating barrier. The CIS effect is here studied in TJs with two thin (20 \AA) non-magnetic (NM) Ta electrodes inserted above and below the insulating barrier. We observe resistance (R) switching for positive applied electrical current (flowing from the bottom to the top lead), characterized by a continuous resistance decrease and associated with current-driven displacement of metallic ions from the bottom electrode into the barrier (thin barrier state). For negative currents, displaced ions return into their initial positions in the electrode and the electrical resistance gradually increases (thick barrier state). We measured the temperature (T) dependence of the electrical resistance of both thin- and thick-barrier states ($R_b$ and R$_B$ respectively). Experiments showed a weaker R(T) variation when the tunnel junction is in the $R_b$ state, associated with a smaller tunnel contribution. By applying large enough electrical currents we induced large irreversible R-decreases in the studied TJs, associated with barrier degradation. We then monitored the evolution of the R(T) dependence for different stages of barrier degradation. In particular, we observed a smooth transition from tunnel- to metallic-dominated transport. The initial degradation-stages are related to irreversible barrier thickness decreases (without the formation of pinholes). Only for later barrier degradation stages do we have the appearance of metallic paths between the two electrodes that, however, do not lead to metallic dominated transport for small enough pinhole radius.Comment: 10 pages, 3 figure

Protogynous Interval in Elephantgrass (Pennisetum purpureum Schum.)

A study was carried out to examine the protogyny duration in elephantgrass inflorescences. Nine accessions were selected, divided into three groups, according to early, intermediate or late flowering. From each cultivar, 10 panicles were sampled for evaluation. The criterion for estimating the duration of protogyny was the time interval (number of days) from the first visual detection of exserted stigmas up to the first visual appearance of open anthers (±5%). Duration of protogyny averaged 7.43±1.37 d, confirming that the species is protoginous. Late flowering accessions exhibited an average of 8.97 d for the duration of protogyny, which was significantly higher than the values observed for the intermediate and early flowering accessions. Data also indicate that the duration of protogyny in elephantgrass is efficient to prevent panicle selfcrossing