4,401 research outputs found
On the Influence of Magnetic Fields on the Structure of Protostellar Jets
We here present the first results of fully three-dimensional (3-D) MHD
simulations of radiative cooling pulsed (time-variable) jets for a set of
parameters which are suitable for protostellar outflows. Considering different
initial magnetic field topologies in approximate with the
thermal gas, i.e., (i) a longitudinal, and (ii) a helical field, both of which
permeating the jet and the ambient medium; and (iii) a purely toroidal field
permeating only the jet, we find that the overall morphology of the pulsed jet
is not very much affected by the presence of the different magnetic field
geometries in comparison to a nonmagnetic calculation. Instead, the magnetic
fields tend to affect essentially the detailed structure and emission
properties behind the shocks at the head and at the pulse-induced internal
knots, particularly for the helical and toroidal geometries. In these cases, we
find, for example, that the emissivity behind the internal knots can
be about three to four times larger than that of the purely hydrodynamical jet.
We also find that some features, like the nose cones that often develop at the
jet head in 2-D calculations involving toroidal magnetic fields, are smoothed
out or absent in the 3-D calculations.Comment: 13 pages, 3 figures, Accepted by ApJ Letters after minor corrections
(for high resolution figures, see http://www.iagusp.usp.br/~adriano/h.tar
Magnetic Field Effects on the Head Structure of Protostellar Jets
We present the results of 3-D SPMHD numerical simulations of
supermagnetosonic, overdense, radiatively cooling jets. Two initial magnetic
configurations are considered: (i) a helical and (ii) a longitudinal field. We
find that magnetic fields have important effects on the dynamics and structure
of radiative cooling jets, especially at the head. The presence of a helical
field suppresses the formation of the clumpy structure which is found to
develop at the head of purely hydrodynamical jets. On the other hand, a cooling
jet embedded in a longitudinal magnetic field retains clumpy morphology at its
head. This fragmented structure resembles the knotty pattern commonly observed
in HH objects behind the bow shocks of HH jets. This suggests that a strong
(equipartition) helical magnetic field configuration is ruled out at the jet
head. Therefore, if strong magnetic fields are present, they are probably
predominantly longitudinal in those regions. In both magnetic configurations,
we find that the confining pressure of the cocoon is able to excite
short-wavelength MHD K-H pinch modes that drive low-amplitude internal shocks
along the beam. These shocks are not strong however, and it likely that they
could only play a secondary role in the formation of the bright knots observed
in HH jets.Comment: 14 pages, 2 Gif figures, uses aasms4.sty. Also available on the web
page http://www.iagusp.usp.br/preprints/preprint.html. To appear in The
Astrophysical Journal Letter
Applicability of low macrobending loss hollow-core PCF to FTTH applications
Fiber-To-The-Home (FTTH) technology has been significantly implemented in access networks, providing very high data rates transmission and a variety of digital content to subscribers. It involves an optical cable link being installed between the building entry point and each subscriber with the Multiple Dwelling Units (MDUs), i.e. flats and apartments. In other words, optical cable has to lie fairly straight to carry a strong signal, since typically is necessary to bend, twist and turn the lines in and out of tight corners without degrading the link connection. In this paper we propose the use of Hollow-Core Photonic Crystal Fiber (HC-PCF) for FTTH applications. It is presented an experimental analysis of the macrobending effects in a HC-PCF based on a comparison with traditional fibers and by following the ITU-T G.657B standard recommendations. We observe this fiber, with only 6.5 µm core, is bending loss insensitive, even at extremely small bending radius of 2 mm, in which it presents a loss of only 0.58 dB.251258Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES
Alterações de açúcares e amido em Banana 'Grande Naine' durante o amadurecimento.
A banana do cultivar 'Grande Naine' pertence ao grupo AAA, subgrupo Cavendish, com grande capacidade produtiva. Durante o desenvolvimento a banana acumula amido, podendo atingir acima de 20% do peso fresco do fruto. Após o pico de etileno e concomitante pico respiratório esta reserva é rapidamente mobilizada, podendo cair para níveis abaixo de 1% ao mesmo tempo em que ocorre a elevação na concentração de sólidos solúveis para valores próximos a 12%. Esse trabalho teve como objetivo avaliar as transformações relativas aos teores de amido e açúcares ao longo do amadurecimento de banana do cultivar 'Grande Naine', gerando informações sobre esta cultivar para o programa de melhoramento genético. Foram realizadas análises de teor de amido, teor de sólidos solúveis, açúcares totais e redutores. O delineamento experimental foi IC com 6 repetições de 2 frutos. O avanço pelos estádios de amadurecimento refletiu na redução dos teores de amido e aumento dos sólidos solúveis. As principais mudanças nas variáveis estudadas foram observadas entre os estádios 3 e 4. Com os dados obtidos foi possível acompanhar o comportamento do metabolismo dos açúcares da banana 'Grande Naine' produzida em Cruz das Almas
Seleção de híbridos de bananeira ornamental obtidos de cruzamentos entre as seções Musa e Rhodochlamys.
A bananeira ornamental constitui-se numa alternativa promissora para o segmento das fruteiras ornamentais. No Brasil, alguns genótipos já são comercializados, como a Musa coccinea, M. ornata e M. velutina, no entanto, seu uso ainda é discreto e pouco explorado. A geração de novas variedades torna-se relevante nesse aspecto, haja vista que o mercado de flores e plantas ornamentais demanda por materiais inovadores
Magnetically Driven Outflows in a Starburst Environment
We here investigate the possibility that the observed collimated outflows in
luminous infrared galaxies (LIGs) and some Seyfert galaxies can be produced in
a starburst (SB) environment. A nuclear disk can be quickly produced by gas
infall during star formation in a rotating, stellar cluster. We find that
massive nuclear SBs with core disk masses M_d \sim 10^8 - 10^9 M_{\odot}, and
supernova rates \nu_{SN} \simeq 5 \times 10^{-3} - 2 yr^{-1} (which are
consistent with the \nu_{SN} values inferred from the observed non-thermal
radio power in source candidates) may inject kinetic energies which are high
enough to blow out directed flows from the accreting disk surface, within the
SB lifetimes. In our models, the acceleration and collimation of the nuclear
outflow are provided by magnetic fields anchored into the rotating SB-disk. The
emerging outflow carries a kinetic power that is only a small fraction (a few
percent) of the supernovae energy rate produced in the SB. Based on conditions
determined from observed outflows and disks, we find that moderate disk
magnetic fields (\gtrsim 8 \times 10^{-4} G) are able to accelerate the
outflows up to the observed terminal velocities (\lesssim few 100 km s^{-1} in
the case of the Seyfert galaxies, and \sim 400 - 950 km s^{-1} in the case of
the LIGs). The outflow is produced within a wind zone in the disk of radius
\lesssim 100 pc in the LIGs, and \lesssim 10 pc in the Seyferts, with wind mass
loss to disk accretion rate ratios \dot M_w /\dot M_d \gtrsim 0.1 (where \dot
M_d \sim 100 M_{\odot} yr^{-1}). The observation of rotating nuclear disks of
gas within few 100 pc scales in source candidates like the LIG Arp 220, and
magnetized outflows provide observational support for the picture drawn here.Comment: 31 pages, Latex file, 1 Figure, accepted for publication in the
Astrophys. Journa
Magnetic Field Effects on the Structure and Evolution of Overdense Radiatively Cooling Jets
We investigate the effect of magnetic fields on the propagation dynamics and
morphology of overdense, radiatively cooling, supermagnetosonic jets, with the
help of fully three-dimensional SPMHD simulations. Evaluated for a set of
parameters which are mainly suitable for protostellar jets (with density ratios
between the jet and the ambient medium 3-10, and ambient Mach number ~ 24),
these simulations are also compared with baseline non-magnetic and adiabatic
calculations. We find that, after amplification by compression and
re-orientation in nonparallel shocks at the working surface, the magnetic field
that is carried backward with the shocked gas into the cocoon improves the jet
collimation relative to the purely hydrodynamic (HD) systems. Low-amplitude,
approximately equally spaced internal shocks (which are absent in the HD
systems) are produced by MHD K-H reflection pinch modes. The longitudinal field
geometry also excites non-axisymmetric helical modes which cause some beam
wiggling. The strength and amount of these modes are, however, reduced (by ~
twice) in the presence of radiative cooling relative to the adiabatic cases.
Besides, a large density ratio between the jet and the ambient medium also
reduces, in general, the number of the internal shocks. As a consequence, the
weakness of the induced internal shocks makes it doubtful that the magnetic
pinches could produce by themselves the bright knots observed in the overdense,
radiatively cooling protostellar jets.Comment: To appear in ApJ; 36 pages + 16 (gif) figures. PostScript files of
figures are available at http://www.iagusp.usp.br/preprints/preprint.htm
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