7,028 research outputs found
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
Interação entre efeito materno e sexo do bezerro para pesos e taxas de crescimento do nascimento à desmama em animais cruzados 5/8 Zebu + 3/8 Charolês.
Analisaram-se os dados de 130 animais nascidos de agosto a novembro dos anos de 1950 a 1952, com o objetivo de avaliar o efeito do tipo de cruzamento no desempenho ate a desmama de bezerros 5/8 Zebu + 3/8 Charoles, criados a pasto na Fazenda Canchim, São Carlos, SP
Análise conjuntural da cultura do arroz nas regiões brasileiras.
O presente trabalho teve por objetivo analisar e demonstrar o movimento migratório da cultura do arroz em termos de área plantada e volume de produção nas regiões Norte, Nordeste, Centro-Oeste, Sudeste e Sul do Brasil nas safras de 1978/79, 1988/89, 1998/1999 e 2008/2009
Cenário energético brasileiro e o potencial do capim-elefante como fonte de matéria-prima para a produção de energia renovável
Os cultivos dedicados à produção de biomassa (dedicated energy crops) podem promover grandes ganhos com a geração de energia renovável, principalmente em regiões de origem tropical e subtropical, devido a grande disponibilidade de energia solar, bem como de terras agricultáveis e recursos hídricos, condições estas encontradas no Brasil.bitstream/item/123070/1/06-Cenario-energetico.pd
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