5,809 research outputs found
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
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
Single and Double Photoionization and Photodissociation of Toluene by Soft X-rays in Circumstellar Environment
The formation of polycyclic aromatic hydrocarbons (PAHs) and their methyl
derivatives occurs mainly in the dust shells of asymptotic giant branch (AGB)
stars. The bands at 3.3 and 3.4 m, observed in infrared emission spectra
of several objects, are attributed C-H vibrational modes in aromatic and
aliphatic structures, respectively. In general, the feature at 3.3 m is
more intense than the 3.4 m. Photoionization and photodissociation
processes of toluene, the precursor of methylated PAHs, were studied using
synchrotron radiation at soft X-ray energies around the carbon K edge with
time-of-flight mass spectrometry. Partial ion yields of a large number of ionic
fragments were extracted from single and 2D-spectra, where electron-ion
coincidences have revealed the doubly charged parent-molecule and several
doubly charged fragments containing seven carbon atoms with considerable
abundance. \textit{Ab initio} calculations based on density functional theory
were performed to elucidate the chemical structure of these stable dicationic
species. The survival of the dications subjected to hard inner shell ionization
suggests that they could be observed in the interstellar medium, especially in
regions where PAHs are detected. The ionization and destruction of toluene
induced by X-rays were examined in the T Dra conditions, a carbon-rich AGB
star. In this context, a minimum photodissociation radius and the half-life of
toluene subjected to the incidence of the soft X-ray flux emitted from a
companion white dwarf star were determined.Comment: 11 pages, 4 figures, accept for publication in Ap
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 . We compare our theoretical result with a precise
measurement of this cross section at 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
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
Distribuicao espacial do tucunare, Cichla sp (Pisces, cichlidae), peixe amazonico introduzido no Pantanal, Brasil.
O tucunare, uma especie exotica, introduzido da bacia Amazonica, tem sido observado no Pantanal desde 1982 no Rio Piquiri, na divisa dos estados de Mato Grosso e Mato Grosso do Sul. Entre novembro de 1992 e janeiro de 1994 foram realizadas 5 campanhas ao longo da bacia do rio Piquiri e no rio Sao Lourenco, acima e abaixo da sua juncao com o rio Piquiri. Exemplares de tucunare foram encontrados em lagos marginais, sugerindo que possivelmente utilizam o rio somente como "corredor". Os limites da distribuicao foram definidos como: 17o28'59"S, 55o13'45"O (abertura da passagem subterranea do rio Correntes); 17o21'20"S, 54o30'25"O (cachoeira Itiquira); 17o18'44"S, 56o43'24"O (boca do rio Piquiri). Portanto, ocorrendo somente na bacia do Piquiri. A transparencia (medida atraves do disco de Secchi) do rio Sao Lourenco e menor que a do rio Piquiri, (22 e 39 cm, e 50 e 70 cm, respectivamente). A baixa transparencia e o reduzido numero de ambientes lenticos, o habitat preferencial das especies, e a longa distancia entre os mesmos no rio Sao Lourenco, podem estar atuando como uma barreira a dispersao do tucunare.bitstream/item/37428/1/BP24.pd
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
- …