Five-Dimensional QED, Muon Pair Production and Correction to the Coulomb Potential

We consider QED in five dimensions in a configuration where matter is localized on a 3-brane while foton propagates in the bulk. The idea is to investigate the effects of the Kaluza-Klein modes of the photon in the relativistic regime, but in low energy, and in the nonrelativistic regime. In the relativistic regime, we calculate the cross section for the reaction $e^+ + e^- \to \mu^+ + \mu^-$. We compare our theoretical result with a precise measurement of this cross section at $\sqrt{s}=57.77$ GeV. As result, we extract a lower bound on the size of the extra dimension. In the nonrelativistic regime, we derive the contribution for the Coulomb potential due to the whole tower of the Kaluza-Klein excited modes of the photon. We use the modified potential to calculate the Rutherford scattering differential cross section.Comment: minor changes, three new refs. added, to appear in IJMP

The Godel metric in the Chern-Simons modified gravity

We discuss the consistency of the Godel metric within the Chern-Simons modified gravity, both for external and dynamical Chern-Simons coefficients.Comment: 6 pages; to be published in the Proceedings of 5th International Workshop on Astronomy and Relativistic Astrophysics (IWARA 2011), matches the accepted versio

Experimental and theoretical evidences for the ice regime in planar artificial spin ices

In this work, we explore a kind of geometrical effect in the thermodynamics of artificial spin ices (ASI). In general, such artificial materials are athermal. Here, We demonstrate that geometrically driven dynamics in ASI can open up the panorama of exploring distinct ground states and thermally magnetic monopole excitations. It is shown that a particular ASI lattice will provide a richer thermodynamics with nanomagnet spins experiencing less restriction to flip precisely in a kind of rhombic lattice. This can be observed by analysis of only three types of rectangular artificial spin ices (RASI). Denoting the horizontal and vertical lattice spacings by a and b, respectively, then, a RASI material can be described by its aspect ratio $\gamma$=a/b. The rhombic lattice emerges when $\gamma$=$\sqrt{3}$. So, by comparing the impact of thermal effects on the spin flips in these three appropriate different RASI arrays, it is possible to find a system very close to the ice regime

Staphylococcus aureus: importância para a saída pública e aspectos epidemiológicos.

Características do staphylococcus aureus. Intoxicação alimentar: aspectos epidemiólogicos.bitstream/CNPAB-2010/27353/1/doc114.pd

Generation of higher derivatives operators and electromagnetic wave propagation in a Lorentz-violation scenario

We study the perturbative generation of higher-derivative operators as corrections to the photon effective action, which are originated from a Lorentz violation background. Such corrections are obtained, at one-loop order, through the proper-time method, using the zeta function regularization. We focus over the lowest order corrections and investigate their influence in the propagation of electromagnetic waves through the vacuum, in the presence of a strong, constant magnetic field. This is a setting of experimental relevance, since it bases active efforts to measure non linear electromagnetic effects. After surprising cancellations of Lorentz violating corrections to the Maxwell's equation, we show that no effects of the kind of Lorentz violation we consider can be detected in such a context.Comment: v2: 13 pages, no figures, section IV considerably rewritten, main results unchanged and are now obtained in a simpler way. To appear in PL

Descrição das larvas das principais espécies de peixes utilizadas pela pesca, no Pantanal.

Elaborou-se uma chave ilustrada, baseando-se na comparacao de caracteristicas morfologicas e morfometricas dos estadios iniciais, quando as larvas ainda sao encontradas no plancton, a deriva no rio. A chave possui a descricao das cinco principais especies utilizadas economicamente no Pantanal: pacu (Piaractus mesopotamicus), curimbata (Prochilodus lineatus), dourado (Salminus maxillosus), piavucu (Leporinus macrocephalus). As especies pintado (Pseudoplatystoma corruscans) e cachara (Pseudoplatystoma fasciatum), por nao apresentarem nenhuma diferenca nas caracteristicas utilizadas nas descricoes, foram incluidas em Pseudoplatystoma sp. As descricoes foram feitas a partir de amostras obtidas em condicoes artificiais.bitstream/item/37433/1/BP19.pd

Alimentacao do tucunare Cichla sp. (Pisces, cichlidae) um peixe introduzido no Pantanal, Brasil.

Com o objetivo de estudar a alimentacao do tucunare (Cichla sp.) no Pantanal, foram realizadas cinco coletas entre novembro/1992 e junho/1994. Foram capturados 425 especimes, destes 207 apresentaram conteudo estomacal. Foram analisadas a Frequencia de Ocorrencia (FO), Volume Relativo (Vr) e "Indice Alimentar" (IA). Os peixes foram o principal item alimentar (FO=97,10%, Vr=96,45, IAi=99,81%), seguido de "restos vegetais", (FO=6,28%, Vr=2,49, IAi=16%) e camaroes (FO=1,93%, Vr=1,04, IAi=2%). Foram identificadas 21 especies de peixes no conteudo estomacal do "tucunare". Curimatella dorsalis foi a presa predominante em numero de individuos (18,75%) e em biomassa (28,81%). A familia mais representativa em biomassa foi Curimatidae (27,36%) e Cichlidae (26,93%); em numero de individuos, Sternopygidae foi mais representada (26,66%), seguida de Cichlidae e Curimatidae, com 15,55%. Os resultados permitem caracterizar o tucunare como piscivoro generalista.bitstream/item/37429/1/BP23.pd