Ambipolar Filamentation of Turbulent Magnetic Fields : A numerical simulation

We present the results of a 2-D, two fluid (ions and neutrals) simulation of the ambipolar filamentation process, in which a magnetized, weakly ionized plasma is stirred by turbulence in the ambipolar frequency range. The higher turbulent velocity of the neutrals in the most ionized regions gives rise to a non-linear force driving them out of these regions, so that the initial ionization inhomogeneities are strongly amplified. This effect, the ambipolar filamentation, causes the ions and the magnetic flux to condense and separate from the neutrals, resulting in a filamentary structure.Comment: 8 pages, 6 figures, accepted for publication in A&

Otimização da detecção de isotiocianatos na análise por CG-DNP.

bitstream/CTAA-2009-09/9978/1/ct100-2006.pd

Determinação de aflatoxinas em milho por cromatografia líquida de alta eficiência com detecção por fluorescência - CLAE/DF.

bitstream/item/84132/1/2009-CTE-0158.pd

Formation of X-ray emitting stationary shocks in magnetized protostellar jets

X-ray observations of protostellar jets show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary. They are interpreted as shock diamonds. We aim at investigating the physics that guides the formation of X-ray emitting stationary shocks in protostellar jets, the role of the magnetic field in determining the location, stability, and detectability in X-rays of these shocks, and the physical properties of the shocked plasma. We performed a set of 2.5-dimensional magnetohydrodynamic numerical simulations modelling supersonic jets ramming into a magnetized medium and explored different configurations of the magnetic field. The model takes into account the most relevant physical effects, namely thermal conduction and radiative losses. We compared the model results with observations, via the emission measure and the X-ray luminosity synthesized from the simulations. Our model explains the formation of X-ray emitting stationary shocks in a natural way. The magnetic field collimates the plasma at the base of the jet and forms there a magnetic nozzle. After an initial transient, the nozzle leads to the formation of a shock diamond at its exit which is stationary over the time covered by the simulations (~ 40 - 60 yr; comparable with time scales of the observations). The shock generates a point-like X-ray source located close to the base of the jet with luminosity comparable with that inferred from X-ray observations of protostellar jets. For the range of parameters explored, the evolution of the post-shock plasma is dominated by the radiative cooling, whereas the thermal conduction slightly affects the structure of the shock.Comment: Accepted for publication in Astronomy and Astrophysic

Determinação de metil-xantinas em alimentos por cromatografia líquida de alta eficiência.

bitstream/item/75983/1/ct55-2002.pd

Aspectos funcionais e nutricionais do tomate: uso de agrotóxicos na tomaticultura de São José de Ubá (RJ).

bitstream/item/108098/1/2008-DOC-0095.pd

Resíduos de agrotóxicos em grãos, casca e farelo de arroz irrigado.

bitstream/item/78838/1/Circular-130.pd

Monitoramento de resíduos de carbofuran no plantio de banana 'prata anã' utilizando diferentes tratamentos químicos.

bitstream/CTAA-2009-09/8946/1/ct79-2005.pd

Relativistic confinement of neutral fermions with a trigonometric tangent potential

The problem of neutral fermions subject to a pseudoscalar potential is investigated. Apart from the solutions for $E=\pm mc^{2}$, the problem is mapped into the Sturm-Liouville equation. The case of a singular trigonometric tangent potential ($\sim \mathrm{tan} \gamma x$) is exactly solved and the complete set of solutions is discussed in some detail. It is revealed that this intrinsically relativistic and true confining potential is able to localize fermions into a region of space arbitrarily small without the menace of particle-antiparticle production.Comment: 12 page