297 research outputs found
Lithium abundance evolution in open clusters: Hyades, NGC752, and M67
Mixing mechanisms bring the Li from the base of the convective zone to deeper
and warmer layers where it is destroyed. These mechanisms are investigated by
comparing observations of Li abundances in stellar atmospheres to models of
stellar evolution. Observations in open cluster are especially suitable for
this comparison, since their age and metallicity are homogeneous among their
members and better determined than in field stars. In this work, we compare the
evolution of Li abundances in three different clusters: the Hyades, NGC752, and
M67. Our models are calculated with microscopic diffusion and transport of
chemicals by meridional circulation, and calibrated on the Sun. These
comparisons allow us to follow the evolution of Li abundance as a function of
stellar mass in each cluster and as a function of the age by comparing this
evolution in each cluster. We evaluate the efficiency of the mixing mechanisms
used in the models, and we try to identify the lacking mechanisms to reproduce
the observed evolution of Li abundance.Comment: 6 pages, 4 figures, conference publication of "New advances in
stellar physics: from microscopic to macroscopic processes
Weaning age effects on some growth and development characteristics of Nelore calves at pasture
O objetivo do presente trabalho foi o de acompanhar o desenvolvimento de bezerros, em regime exclusivo de pasto, submetidos a desmama precoce. Assim, bezerros e bezerras Nelore foram desmamados nas idades de três, cinco e sete meses. Nos bezerros, o desenvolvimento foi acompanhado até os doze meses, tendo a esta idade apresentado os pesos de 146 (D3), 155 (D5) e 172kg (D7), respectivamente. Não houve diferença significativa entre os pesos aos três e cinco meses e entre cinco e sete meses. No entanto, a elevada mortalidade, decorrente do estresse da desmama aos três meses desaconselha essa prática em condições semelhantes às do experimento. As fêmeas desmamadas nas mesmas idades, três, cinco e sete meses, não mostraram diferenças nos pesos aos 12 e 24 meses, peso à fecundação e idade ao primeiro parto, que foram, em media, de 152 kg, 252 kg, 318 kg e 1.279 dias, respectivamente. No entanto, as novilhas com segunda recria em campo limpo tiveram a primeira parição 2,8 meses mais tarde que as de segunda recria em Jaraguá, e isto, possivelmente por terem atingido o peso ideal pra a fecundação mais tardiamente. A idade ao primeiro parto pra novilhas que foram desmamadas aos três, cinco e sete meses foi de 1.274, 1.289 e 1.275 dias, respectivamente. Concluiu-se que a desmama aos cinco meses pode ser adotada sem afetar o crescimento e o bom desenvolvimento do bezerro.The objective of this experiment was to evaluate some growth characteristics of Nelore calves, raised at pastures and weaned at two early ages (three, five and seven months). Male yearling weights were 146 (W3), 155 (E5) and 172 kg (W7), for weaning at the, five and 7 months, respectively. There was no difference between W3 and W5 or between W5 and W7. A high mortality was observed in the first group. Female weights at 12 and 24 months and at conception, and the age at first parturition were not affected (P < 0.05) by weaning age. The mean squares for these characteristics were 152 kg, 252 kg, 318 kg and 1,279 days, respectively. Based on the results it is concluded that weaning at five months may be practiced without interfering with calf growth, and development
The effects of stellar winds on the magnetospheres and potential habitability of exoplanets
Context: The principle definition of habitability for exoplanets is whether
they can sustain liquid water on their surfaces, i.e. that they orbit within
the habitable zone. However, the planet's magnetosphere should also be
considered, since without it, an exoplanet's atmosphere may be eroded away by
stellar winds. Aims: The aim of this paper is to investigate magnetospheric
protection of a planet from the effects of stellar winds from solar-mass stars.
Methods: We study hypothetical Earth-like exoplanets orbiting in the host
star's habitable zone for a sample of 124 solar-mass stars. These are targets
that have been observed by the Bcool collaboration. Using two wind models, we
calculate the magnetospheric extent of each exoplanet. These wind models are
computationally inexpensive and allow the community to quickly estimate the
magnetospheric size of magnetised Earth-analogues orbiting cool stars. Results:
Most of the simulated planets in our sample can maintain a magnetosphere of ~5
Earth radii or larger. This suggests that magnetised Earth analogues in the
habitable zones of solar analogues are able to protect their atmospheres and is
in contrast to planets around young active M dwarfs. In general, we find that
Earth-analogues around solar-type stars, of age 1.5 Gyr or older, can maintain
at least a Paleoarchean Earth sized magnetosphere. Our results indicate that
planets around 0.6 - 0.8 solar-mass stars on the low activity side of the
Vaughan-Preston gap are the optimum observing targets for habitable Earth
analogues.Comment: 8 pages, 3 figures, accepted to Astronomy and Astrophysic
Stellar Cycles in Fully Convective Stars and a New Interpretation of Dynamo Evolution
An dynamo, combining shear and cyclonic convection in the
tachocline, is believed to generate the solar cycle. However, this model cannot
explain cycles in fast rotators (with minimal shear) or in fully convective
stars (no tachocline); analysis of such stars could therefore provide key
insights into how these cycles work. We reexamine ASAS data for 15 M dwarfs, 11
of which are presumed fully convective; the addition of newer ASAS-SN data
confirms cycles in roughly a dozen of them, while presenting new or revised
rotation periods for five. The amplitudes and periods of these cycles follow
, with (where Ro is the Rossby number), very
similar to that we
find for 40 previously studied FGK stars, although
and are a factor of 20 smaller in the M stars. The very
different -Ro relationship seen here compared to
previous work suggests that two types of dynamo, with opposite Ro dependences,
operate in cool stars. Initially, a (likely or )
dynamo operates throughout the convective zone in mid-late M and fast rotating
FGK stars, but once magnetic breaking decouples the core and convective
envelope, a tachocline dynamo begins and eventually dominates in
older FGK stars. A change in in the tachocline dynamo generates the
fundamentally different -Ro relationship.Comment: 26 pages, 18 figures, submitted to ApJ. Figure sets will be available
in the final prin
Universo em descoberta: Palestras e noites de observação celeste no Campus Regional de Goioerê
Anais do 35º Seminário de Extensão Universitária da Região Sul - Área temática: ComunicaçãoO projeto busca através de visitas às escolas da região, e praças do
município, para população em geral, divulgar e exemplificar o ensino da astronomia.
O projeto de extensão Universo em Descoberta, vinculado ao Campus Regional da
Universidade Estadual de Maringá em Goioerê/PR. tem como objetivos: estimular
alunos e professores, de todos os níveis de ensino, a desenvolverem atividades que
despertem o interesse pela busca do conhecimento científico; aproximar a
universidade e a comunidade, fornecendo acesso a informações teóricas; e
incentivar a participação em noites de observação celeste realizadas no Campus.
Atualmente alunos da rede pública e particular de ensino são atendidos com
palestras, participações em noite de observações celestes, feira de ciências e muitas
outras atividades, além da divulgação das ciências e tecnologia. Dessa forma
pretende-se compartilhar e evidenciar que atividades envolvendo as ciências e a
Física em espaços diferentes do tradicionalismo de uma sala de aula são de
fundamental importância, tanto para despertar interesse pela Ciência como para
oportunizar a interação escola-universidade-comunidad
Estudo Experimental do Efeito da Argilosidade Sobre as Propriedades Físicas de Solos
This final course work aimed to evaluate the effect of shaliness on the physical properties of clay soils, with emphasis on the properties of porous media. For this, we used a gas poropermeameter based on the pressure variation on confining chamber, in order to obtain values of absolute permeability and effective porosity on unconsolidated sediments (soils). The values for pore volume are obtained by Boyle Mariotte law, which relates the variation of pressure and volume of an ideal gas at constant temperature, while permeability values are obtained by Darcy's law. It is also emphasized the development of a method for analysis of unconsolidated sediments with the equipment since it was designed to consolidated sediments. This includes sample enveloping and studies for determination of ideal pressures and flows to be used. Measured values for permeability and porosity were used in estimating other physical parameter of the sediments, the specific surface of the grains, through the Kozeny-Carman equation, whose constant was considered equal to 5, since this is the value recommended for flow in porous unconsolidated sediments. Results show that this equipment can be used successfully for measurements of physical pore properties of soils if samples are properly prepared.Neste trabalho foi avaliado o efeito da argilosidade sobre as propriedades físicas de solos argilosos, com ênfase na porosidade e na permeabilidade do meio. Para isto foi utilizado o equipamento permo-porosímetro a gás, baseado na variação de pressão em câmara confinante, com o intuito de obter valores de porosidade efetiva e permeabilidade absoluta em sedimentos inconsolidados (solos). No procedimento foram utilizadas amostras sintéticas, usando diferentes proporções de quantidades de esferas de vidro e caulinita (argila), com a intenção de criar um padrão granulométrico das amostras a serem analisadas. Isto incluiu a preparação do invólucro da amostra e estudos da determinação das pressões e fluxos de fluidos a serem aplicados nas amostras, fundamentados em publicações científicas. Os valores obtidos de permeabilidade e porosidade foram utilizados na estimativa de outro parâmetro físico dos sedimentos, a superfície específica dos grãos através da equação de Kozeny-Carman, cujo valor da constante recomendado por outros autores é igual a 5, para fluxo em meios porosos inconsolidados. Pode-se verificar nos resultados que o permo-porosímetro a gás, pode ser utilizado com sucesso na medição das propriedades físicas de solos tanto arenosos como argilosos
- …