Counter-rotation in relativistic magnetohydrodynamic jets

Young stellar object observations suggest that some jets rotate in the opposite direction with respect to their disk. In a recent study, Sauty et al. (2012) have shown that this does not contradict the magnetocentrifugal mechanism that is believed to launch such outflows. Signatures of motions transverse to the jet axis and in opposite directions have recently been measured in M87 (Meyer et al. 2013). One possible interpretation of this motion is the one of counter rotating knots. Here, we extend our previous analytical derivation of counter-rotation to relativistic jets, demonstrating that counter-rotation can indeed take place under rather general conditions. We show that both the magnetic field and a non-negligible enthalpy are necessary at the origin of counter-rotating outflows, and that the effect is associated with a transfer of energy flux from the matter to the electromagnetic field. This can be realized in three cases : if a decreasing enthalpy causes an increase of the Poynting flux, if the flow decelerates, or, if strong gradients of the magnetic field are present. An illustration of the involved mechanism is given by an example of relativistic MHD jet simulation.Comment: Accepted for publication in ApJ

CAVITATION EROSION MICRO-JETS STUDIES OF ALUMINUM SPECIMENS WITH THE AID OF THE COMPACT ROTATING DISK DEVICE

The shape of micro-jets created in the final stages of cavities collapses are studied here with the goal to explain the shape of the pits, formed on the surface of commercial aluminum specimens.These marks on the specimen surfaces are obtained experimentally with the aid of the compact rotating disk device and a scanning electronic microscope. Some explain is attempt, based on the theories of the potential flow and forms

Eficiência da mosca doméstica na polinização controlada de cebola no semi-árido de Pernambuco.

Com o objetivo de efetuar polinizações controladas (aufecundações ou ?bulks?) em cebola, dentro de gaiolas individuais com 2 x 3 m, a mosca foi escolhida por ser de fácil criação, manuseio e sem agressividade, como as abelhas

Accelerating Cold Dark Matter Cosmology (ΩΛ≡0\Omega_{\Lambda}\equiv 0)

A new kind of accelerating flat model with no dark energy that is fully dominated by cold dark matter (CDM) is investigated. The number of CDM particles is not conserved and the present accelerating stage is a consequence of the negative pressure describing the irreversible process of gravitational particle creation. A related work involving accelerating CDM cosmology has been discussed before the SNe observations [Lima, Abramo & Germano, Phys. Rev. D53, 4287 (1996)]. However, in order to have a transition from a decelerating to an accelerating regime at low redshifts, the matter creation rate proposed here includes a constant term of the order of the Hubble parameter. In this case, $H_0$ does not need to be small in order to solve the age problem and the transition happens even if the matter creation is negligible during the radiation and part of the matter dominated phase. Therefore, instead of the vacuum dominance at redshifts of the order of a few, the present accelerating stage in this sort of Einstein-de Sitter CDM cosmology is a consequence of the gravitational particle creation process. As an extra bonus, in the present scenario does not exist the coincidence problem that plagues models with dominance of dark energy. The model is able to harmonize a CDM picture with the present age of the universe, the latest measurements of the Hubble parameter and the Supernovae observations.Comment: 9 pages, 6 figures, typos corrected, references added, discussion in Appendix B extende

Exact Curie temperature for the Ising model on Archimedean and Laves lattices

Using the Feynman-Vdovichenko combinatorial approach to the two dimensional Ising model, we determine the exact Curie temperature for all two dimensional Archimedean lattices. By means of duality, we extend our results to cover all two dimensional Laves lattices. For those lattices where the exact critical temperatures are not exactly known yet, we compare them with Monte Carlo simulations.Comment: 10 pages, 1 figures, 3 table

Ação de óleos e extratos vegetais no controle de Rhipicephalus (Boophilus) microplus in vitro.

A infestação por carrapatos é um dos principais entraves à produção de leite isento de resíduos. O objetivo deste estudo foi avaliar a eficácia in vitro dos óleos de Pilocarpus microphyllus (jaborandi) e Citrus sp (laranja), bem como dos extratos etanólico e aquoso e óleo de Azadirachta indica (nim) no controle de fêmeas ingurgitadas de Rhipicephalus (Boophilus) microplus. Os bioensaios foram realizados pelo método de imersão das carrapatas. O óleo de laranja e o extrato etanólico das folhas do nim inibiram significativamente a reprodução das carrapatas somente quando em concentrações elevadas, portanto, outros estudos devem ser realizados com intuito de aumentar a concentração dos princípios ativos e a eficácia destes produtos.Edição dos Resumos do 7º Congresso Brasileiro de Agroecologia, Fortaleza-CE, dez. 2011

Atributos químicos e físicos de Terras Pretas de Índio (TPI) de várzea e terra firme na calha do rio Solimões/Amazonas.

O objetivo desse trabalho foi comparar perfis de TPI encontrados na várzea do Solimões com TPI de Terras Firme associados ao mesmo rio