22,548 research outputs found
Modeling non-thermal emission from stellar bow shocks
Runaway O- and early B-type stars passing throughout the interstellar medium
at supersonic velocities and characterized by strong stellar winds may produce
bow shocks that can serve as particle acceleration sites. Previous theoretical
models predict the production of high energy photons by non-thermal radiative
processes, but their efficiency is still debated. We aim to test and explain
the possibility of emission from the bow shocks formed by runaway stars
traveling through the interstellar medium by using previous theoretical models.
We apply our model to AE Aurigae, the first reported star with an X-ray
detected bow shock, to BD+43 3654, in which the observations failed in
detecting high energy emission, and to the transition phase of a supergiant
star in the late stages of its life.From our analysis, we confirm that the
X-ray emission from the bow shock produced by AE Aurigae can be explained by
inverse Compton processes involving the infrared photons of the heated dust. We
also predict low high energy flux emission from the bow shock produced by BD+43
3654, and the possibility of high energy emission from the bow shock formed by
a supergiant star during the transition phase from blue to red supergiant.Bow
shock formed by different type of runaway stars are revealed as a new possible
source of high energy photons in our neighbourhood
Toward a test of angular momentum coherence in a twin-atom interferometer
We present a scheme well-suited to investigate quantitatively the angular
momentum coherence of molecular fragments. Assuming that the dissociated
molecule has a null total angular momentum, we investigate the propagation of
the corresponding atomic fragments in the apparatus. We show that the
envisioned interferometer enables one to distinguish unambiguously a
spin-coherent from a spin-incoherent dissociation, as well as to estimate the
purity of the angular momentum density matrix associated with the fragments.
This setup, which may be seen as an atomic analogue of a twin-photon
interferometer, can be used to investigate the suitability of molecule
dissociation processes -- such as the metastable hydrogen atoms H()-H() dissociation - for coherent twin-atom optics.Comment: 6 pages, 3 Figures. Final version accepted for publication in
Europhysics Letter
Nanotoxicologia aliada à avaliação de riscos ambientais: uma estratégia para avaliações de segurança das nanotecnologias no Brasil.
As mesmas propriedades que tornam as nanopartículas interessantes para aplicações, também as tornam acessíveis a locais anteriormente inacessíveis em sistemas vivos, com conseqüências potencialmente significativas para a nanosegurança. As principais recomendações para a avaliação do risco-benefício e de gerenciamento de risco lidam com aplicações de máximo risco da nanotecnologia, questões de curto e longo prazo, além de modelos de regulamentação global para a nanotecnologia. A avaliação do potencial impacto biológico dos nanomateriais se tornou de grande importância nos últimos anos, pois o rápido ritmo de desenvolvimento da nanotecnologia não foi acompanhado por uma investigação completa de sua segurança
Cultura do girassol: tecnologia de produção.
Escolha da area e preparo do solo; Correcao da acidez; Adubacao; Epoca de plantio; Plantio; Densidade; Controle de plantas daninhas; Doencas e pragas; Colheita.bitstream/item/60796/1/Documentos-67.pd
Cultura do girassol: tecnologia de produção.
Escolha de area e preparo do solo; Correcao da acidez; Adubacao; Epoca de plantio; Plantio; Densidade; Controle de plantas daninhas; Doencas e pragas; Colheita.bitstream/item/61288/1/Documentos-67-1996.pdf2. ed. rev. aum
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