Causal Structure and Birefringence in Nonlinear Electrodynamics

We investigate the causal structure of general nonlinear electrodynamics and determine which Lagrangians generate an effective metric conformal to Minkowski. We also proof that there is only one analytic nonlinear electrodynamics presenting no birefringence.Comment: 11 pages, no figure

Bioprospecção de actinobactérias da rizosfera para produção de metabólitos bioativos.

Actinobactérias rizosféricas, têm mostrado grande potencial na produção de metabólitos bioativos, sendo o gênero das Streptomyces o mais bem estudado e com melhor potencial para produção destes compostos. Assim, o presente trabalho visou realizar a bioprospecção de actinobactérias rizosféricas e avaliar o potencial de seus metabólitos bioativos no controle de bactérias patogênicas. Foram isoladas linhagens de actinobactérias de plantas sadias de milho, cultivado em diferentes regiões edafoclimáticas do Estado de São Paulo. As linhagens foram avaliadas quanto ao potencial de controle de Bacillus megaterium, Escherichia coli, Klebsiella spp., Pseudomonnas aeruginosa e Sthaphylococcus aureus. Os isolados que se mostraram eficientes em testes de antagonismo foram utilizados em ensaios de antibiose para verificação do potencial do composto bioativo no controle destes patógenos. Foram isolados 60 actinobactérias, identificadas morfologicamente como sendo do gênero Streptomyces. Dentre estas, 31 inibiram pelo menos 1 dos 5 patógenos em testes de antagonismos. Nos ensaios de antibiose, foi verificada a eficiência dos metabólitos de 25 actinobactérias no controle dos patógenos testados

Bopp-Podolsky black holes and the no-hair theorem

Bopp-Podolsky electrodynamics is generalized to curved space-times. The equations of motion are written for the case of static spherically symmetric black holes and their exterior solutions are analyzed using Bekenstein's method. It is shown the solutions split-up into two parts, namely a non-homogeneous (asymptotically massless) regime and a homogeneous (asymptotically massive) sector which is null outside the event horizon. In addition, in the simplest approach to Bopp-Podolsky black holes, the non-homogeneous solutions are found to be Maxwell's solutions leading to a Reissner-Nordstr\"om black hole. It is also demonstrated that the only exterior solution consistent with the weak and null energy conditions is the Maxwell's one. Thus, in light of energy conditions, it is concluded that only Maxwell modes propagate outside the horizon and, therefore, the no-hair theorem is satisfied in the case of Bopp-Podolsky fields in spherically symmetric space-times.Comment: 9 pages, updated to match published versio

Avaliação dos impactos ambientais e econômicos do controle químico do percevejo-barriga-verde (Dichelops melacanthus) em trigo e milho safrinha.

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Effective interaction between molecules in the BEC regime of a superfluid Fermi gas

We investigate the effective interaction between Cooper-pair molecules in the st rong-coupling BEC regime of a superfluid Fermi gas with a Feshbach resonance. Our work uses a path integral formulation and a renormalization group (RG) analy sis of fluctuations in a single-channel model. We show that a physical cutoff en ergy $\omega_c$ originating from the finite molecular binding energy is the key to understanding the interaction between molecules in the BEC regime. Our work t hus clarifies recent results by showing that $a_{\rm M}=2a_{\rm F}$ is a {\it ba re} molecular scattering length while $a_{\rm M}=(0.6\sim0.75) a_{\rm F}$ is the low energy molecular scattering length renormalized to include high-energy scat tering up to $\omega_c$ (here $a_{\rm F}$ is the scattering length between Fermi atoms). We also include many-body effects at finite temperatures. We find that $a_{\rm M}$ is strongly dependent on temperature, vanishing at $T_{\rm c}$, consistent with the earlier Bose gas results of Bijlsma and Stoof.Comment: 10 pages, 3 figure

Occurrence of microsporidians Glugea hertwigi and Pleistophora ladogensis, in smelt Osmerus eperlanus from two German rivers, North Sea coast

Monthly samples of smelt Osmerus eperlanus (Linnaeus, 1758) were collected from July 1985 to May 1986, in the river Elbe (Germany), and examined for infections with microsporidi ans. Two microsporidians were found: Glugea hertwigi Weissenberg, 1911, infecting the digestive tract and Pleistophora ladogenis Voronin, 1978, infecting the skeletal musculature. G. hertwigi in fection led to the formation of xenomas, whereas P. ladogensis was characterized by diffuse infec tions, with the production of macroscopic visible thread-like or oval-shaped infection foci. Develop ment of G. hertwigi in the host cells showed characteristics typical of the genus Glugea. The ultrastructural development of P. ladogensis showed features typical of the genus Pleistophora, without evidence of the production of 2 types of spores. Host reaction consisted of inflammatory tis sue surrounding some of the infection foci as well as phagocytosis of spores. G. hertwigi was only found in juvenile smelt (<10 cm in length), whereas P. ladogensis infected smelts from 6 to 26 cm in length. Prevalence increased with fish length to a maximum value of 9.6%. Seasonal fluctuations in prevalence of infection were also found, with the lowest value in the winter months (2.5% in January 1986) and the highest in summer (11.8% in July 1985). The differences in prevalence of in fection with fish length and date of sampling were significant. Additionally, samples of smelt caught in April 1986 from the rivers Eider and Ems revealed infections with P. ladogensis in the first river system only.info:eu-repo/semantics/publishedVersio

Difusão e validação de tecnologias para a sustentabilidade da agricultura familiar do Estado de Goiás.

O objetivo deste trabalho foi selecionar cultivares e linhagens de arroz e feijão adaptadas ao sistema de produção dos pequenos agricultores, por meio da implementação de ensaios de VCU (Valor de cultivo e uso) e unidades demonstrativas nas propriedades dos agricultores em Goiás; produzir sementes da variedade Samambaia e criar uma relação de cooperação entre pesquisadores e produtores, na qual o produtor familiar é colocado também na condição de pesquisador e responsável pela preservação dos recursos naturais