21,173 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
AE Aurigae: first detection of non-thermal X-ray emission from a bow shock produced by a runaway star
Runaway stars produce shocks when passing through interstellar medium at
supersonic velocities. Bow shocks have been detected in the mid-infrared for
several high-mass runaway stars and in radio waves for one star. Theoretical
models predict the production of high-energy photons by non-thermal radiative
processes in a number sufficiently large to be detected in X-rays. To date, no
stellar bow shock has been detected at such energies. We present the first
detection of X-ray emission from a bow shock produced by a runaway star. The
star is AE Aur, which was likely expelled from its birthplace by the encounter
of two massive binary systems and now is passing through the dense nebula IC
405. The X-ray emission from the bow shock is detected at 30" to the northeast
of the star, coinciding with an enhancement in the density of the nebula. From
the analysis of the observed X-ray spectrum of the source and our theoretical
emission model, we confirm that the X-ray emission is produced mainly by
inverse Compton upscattering of infrared photons from dust in the shock front.Comment: Accepted for publication in the Astrophysical Journal with number
ApJ, 757, L6. Four figure
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
Chemical abundances and kinematics of barium stars
In this paper we present an homogeneous analysis of photospheric abundances
based on high-resolution spectroscopy of a sample of 182 barium stars and
candidates. We determined atmospheric parameters, spectroscopic distances,
stellar masses, ages, luminosities and scale height, radial velocities,
abundances of the Na, Al, -elements, iron-peak elements, and s-process
elements Y, Zr, La, Ce, and Nd. We employed the local-thermodynamic-equilibrium
model atmospheres of Kurucz and the spectral analysis code {\sc moog}. We found
that the metallicities, the temperatures and the surface gravities for barium
stars can not be represented by a single gaussian distribution. The abundances
of -elements and iron peak elements are similar to those of field giants
with the same metallicity. Sodium presents some degree of enrichment in more
evolved stars that could be attributed to the NeNa cycle. As expected, the
barium stars show overabundance of the elements created by the s-process. By
measuring the mean heavy-element abundance pattern as given by the ratio
[s/Fe], we found that the barium stars present several degrees of enrichment.
We also obtained the [hs/ls] ratio by measuring the photospheric abundances of
the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and
the [hs/ls] ratios are strongly anti-correlated with the metallicity. Our
kinematical analysis showed that 90% of the barium stars belong to the thin
disk population. Based on their luminosities, none of the barium stars are
luminous enough to be an AGB star, nor to become self-enriched in the s-process
elements. Finally, we determined that the barium stars also follow an
age-metallicity relation.Comment: 30 pages, 26 figures, 18 tables, accepted for publication in MNRA
Avaliação Biológica de Viroses em Plantas Matrizes e Mudas de Batata-doce (Ipomoea batatas).
bitstream/item/30878/1/Circular-75.pd
Avaliação da toxicidade de Piraclostrobin, Epoxiconazol e sua mistura em alga Pseudokirchneriella subcapitata.
Resumo: Estudou-se o efeito toxicológico (inibição de crescimento) de formulações fungicidas à base de piraclostrobin e epoxiconazol, isoladamente e em formulação conjugada, sobre a alga Pseudokirchneriella subcapitata mediante determinação da Concentração Efetiva Média (CE50-72 h) dos princípios ativos de cada uma das formulações. Foram encontrados valores de CE50- 72 h de 5,57 mg.L-1 para a formulação à base de piraclostrobin, de 1,14 mg.L-1 para a formulação à base de epoxiconazol e de 0,20 mg.L-1 para a formulação conjugada. O piraclostrobin apresentou menor toxicidade às algas em relação aos dados encontrados na literatura, o epoxiconazol resultados semelhantes e a mistura maior toxicidade. A análise isobolográfica e a determinação do Índice de Aditividade (IA) sugerem forte sinergismo da mistura quanto à sua ação tóxica sobre o organismo-teste. Esse fato realça a necessidade de revisão dos padrões limitantes desses fungicidas em corpos de água, os quais tendem a subestimar os efeitos adversos resultantes da combinação dos agentes tóxicos
Spatial analysis of erosive processes in plateaus and depressions of the Upper Paraguai river basin.
Natural characteristics may contribute to the erosion of the soil and to environmental imbalances, and in most cases, they initiate the imbalances that will be exacerbated by human activities. The presence of asymmetry in a frequency diagram is a valuable fact, and may indicate irregularity in the occurrence of events or aggregation of events in preferred locations. Thus, this work aims to demonstrate the use of Geographic Information Systems (GIS) of statistical analysis based on patterns of frequency, density, distribution and spatial dependence of sample points through a cutout of the mapping of the geotechnical aspects conducted for the State of Mato Grosso, generated for the entire area of plateaus and depressions of the Upper Paraguai river basin and its internal units of drainage basins. In most cutouts used in the analysis, the values indicated that is void the possibility that the distribution patterns of erosive events were resulted of chance. The aggregate pattern shown may tend to attract new points, facilitating the transmission of the sample’s qualities through these, favored by your proximity and by the characteristics of the occurrence area.Especial - Geopantanal 2016
Ocorrência e duração de dormência em arroz de terras altas e de várzeas.
Este trabalho teve por objetivo verificar a ocorrência de dormência e sua intensidade, em cultivares de arroz de terras altas e de várzeas recomendadas pela Embrapa Arroz e Feijão e seus parceiros, bem como de algumas linhagens promissoras com possibilidades de serem lançadas pelo programa de melhoramento genético.bitstream/CNPAF/18763/1/pqfoco54.pd
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