14,492 research outputs found
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
Avaliação do teor de ácido pirúvico em duas cultivares de cebola: Cascuda Bronzeada Roxa e Cascuda Bronzeada Amarela.
Accelerating Cold Dark Matter Cosmology ()
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,
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
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