12,309 research outputs found
A new library of theoretical stellar spectra with scaled-solar and alpha-enhanced mixtures
Theoretical stellar libraries have been increasingly used to overcome
limitations of empirical libraries, e.g. by exploring atmospheric parameter
spaces not well represented in the latter. This work presents a new theoretical
library which covers 3000 Teff 25000\,K, -0.5 log g
5.5, and 12 chemical mixtures covering 0.0017 Z 0.049 at both
scaled-solar and -enhanced compositions. This library complements
previous ones by providing: (i) homogeneous computations of opacity
distribution functions, models atmospheres, statistical surface fluxes and high
resolution spectra; (ii) high resolution spectra with continua slopes corrected
by the effect of predicted lines, and; (iii) two families of -enhanced
mixtures for each scaled-solar iron abundance, to allow studies of the
-enhancement both at `fixed iron' and `fixed Z' cases. Comparisons to
observed spectra were performed and confirm that the synthetic spectra
reproduce well the observations, although there are wavelength regions which
should be still improved. The atmospheric parameter scale of the model library
was compared to one derived from a widely used empirical library, and no
systematic difference between the scales was found. This is particularly
reassuring for methods which use synthetic spectra for deriving atmospheric
parameters of stars in spectroscopic surveys
Born-Infeld magnetars: larger than classical toroidal magnetic fields and implications for gravitational-wave astronomy
Magnetars are neutron stars presenting bursts and outbursts of X- and
soft-gamma rays that can be understood with the presence of very large magnetic
fields. Thus, nonlinear electrodynamics should be taken into account for a more
accurate description of such compact systems. We study that in the context of
ideal magnetohydrodynamics and make a realization of our analysis to the case
of the well-known Born-Infeld (BI) electromagnetism in order to come up with
some of its astrophysical consequences. We focus here on toroidal magnetic
fields as motivated by already known magnetars with low dipolar magnetic fields
and their expected relevance in highly magnetized stars. We show that BI
electrodynamics leads to larger toroidal magnetic fields when compared to
Maxwell's electrodynamics. Hence, one should expect higher production of
gravitational waves (GWs) and even more energetic giant flares from nonlinear
stars. Given current constraints on BI's scale field, giant flare energetics
and magnetic fields in magnetars, we also find that the maximum magnitude of
magnetar ellipticities should be . Besides, BI electrodynamics
may lead to a maximum increase of order of the GW energy radiated
from a magnetar when compared to Maxwell's, while much larger percentages may
arise for other physically motivated scenarios. Thus, nonlinear theories of the
electromagnetism might also be probed in the near future with the improvement
of GW detectors.Comment: 8 pages, no figures, accepted for publication in The European
Physical Journal C (EPJC
A grid of Synthetic Spectra for Hot DA White Dwarfs and Its Application in Stellar Population Synthesis
In this work we present a grid of LTE and non-LTE synthetic spectra of hot DA
white dwarfs (WDs). In addition to its usefulness for the determination of
fundamental stellar parameters of isolated WDs and in binaries, this grid will
be of interest for the construction of theoretical libraries for stellar
studies from integrated light. The spectral grid covers both a wide temperature
and gravity range, with 17,000 K <= T_eff <= 100,000 K and 7.0 <= log(g) <=
9.5. The stellar models are built for pure hydrogen and the spectra cover a
wavelength range from 900 A to 2.5 microns. Additionally, we derive synthetic
HST/ACS, HST/WFC3, Bessel UBVRI and SDSS magnitudes. The grid was also used to
model integrated spectral energy distributions of simple stellar populations
and our modeling suggests that DAs might be detectable in ultraviolet bands for
populations older than ~8 Gyr.Comment: to be published in The Astrophysical Journal Supplement Serie
Caracterização, classificação, potencialidades e restrições agrícolas de solos em Chapadinha-MA.
O assentamento Malhada do Meio, localizado em Chapadinha-MA, possui uma área de 630,86 ha, a vegetação é de Floresta Estacional Decidual Submontana e Savana Estépica. O relevo é ondulado e plano, com altitude média de 67 m. A geologia é formada por arenitos finos argilosos da Formação Itapecuru e Depósitos Aluvionares e Coluvionares. Objetivou-se neste trabalho caracterizar, classificar e avaliar as potencialidades e as restrições agrícolas dos solos do assentamento de reforma agrária Malhada do Meio, localizado no município de Chapadinha-MA. Foram abertos quatro perfis em pontos distintos da paisagem. Amostras foram coletadas para a realização das análises de caracterização químicas e granulométrica. Os solos estudados foram classificados no Sistema Brasileiro de Classificação de Solos como Plintossolo Pétrico Concrecionário êndico latossólico, Plintossolo Argilúvico Distrófico abrúptico gleissólico, Neossolo Flúvico e Gleissolo Háplico Tb Distrófico cambissólico. As limitações agrícolas entre os solos estudados (baixa fertilidade, drenagem deficiente, impedimentos à mecanização e ao desenvolvimento das raízes) podem restringir a produtividade das culturas agrícolas
Estudo da aclimatação de lodo ativado com efluente “in natura” da industria de pescado
O presente trabalho estudou a adaptação e a atividade do lodo biológico procedente de um
reator UASB de uma estação de tratamento de efluentes de uma indústria de processamento de pescado,
para remoção biológica de nitrogênio em um Reator Batelada Seqüencial instrumentado em escala de
bancada. A adaptação consistiu em aumento seqüencial da carga aplicada nas razões volumétricas efluente
in natura : efluente sintético de 1:3,33; 1:2,5; 1:2,0; sendo a concentração inicial de inóculo empregada de
20 g SSV/L. Durante este período foram acompanhadas as variações de DQO, nitrato e amônia, onde se
obteve uma remoção de até 80% da carga orgânica do efluente e de até 97% da matéria nitrogenada. O
experimento com diluição de 1:3,33 foi realizado com adição de 0,5 % de sal para avaliar o efeito da
salinidade, o qual também é considerado na análise dos resultados obtidos
Estudo da aclimatação da flora microbiana a concentrações crescentes de efluente “in natura” da indústria de pescado em reator batelada sequencial
O presente trabalho estudou a adaptação e a atividade do lodo biológico procedente de um reator UASB de uma estação de tratamento de efluentes de uma indústria de processamento de pescado, para remoção biológica de nitrogênio em um Reator Batelada Seqüencial. A adaptação consistiu em aumento seqüencial da carga aplicada nas razões volumétricas efluente in natura : efluente sintético de 1:3,33; 1:2,5; 1:2,0; sendo a concentração inicial de inóculo empregada de 20 g SSV/L. Durante este período foram acompanhadas as variações de DQO, nitrato e amônia, onde se obteve uma remoção de até 80% da carga orgânica do efluente e de até 97% da matéria nitrogenada. O experimento com diluição de 1:3,33 foi conduzido com adição de 0,5 % de sal (NaCl) para avaliar o efeito da salinidade, o qual também é considerado na análise dos resultados obtidos.The present work analyzes the adaptation and activity of a sludge belonging to a UASB reactor of the
wastewater treatment unit from a fish processing industry, in a bench scale Sequencing Batch Reactor for
biological nitrogen removal. The sludge adaptation was carried using an increasing sequence of the applied load
from 1:3.33; 1:2.5; 1:2.0; regarding to volume of in natura wastewater : synthetic sewage. The initial inocullum
concentration employed was 20 g VSS / L. During this period COD, nitrate and ammonia concentrations were
followed and a removal about 80% of the organic matter and up to 97% of nitrogen could be achieved. An
experiment employing the greater dilution (1:3.33) with 0.5% salt (as NaCl) was also carried to evaluate the
salinity effect which is considered in the analysis of the results herein presented
Nuclear magnetic resonance measurements reveal the origin of the Debye process in monohydroxy alcohols
Monohydroxy alcohols show a structural relaxation and at longer time scales a
Debye-type dielectric peak. From spin-lattice relaxation experiments using
different nuclear probes an intermediate, slower-than-structural dynamics is
identified for n-butanol. Based on these findings and on diffusion
measurements, a model of self-restructuring, transient chains is proposed. The
model is demonstrated to explain consistently the so far puzzling observations
made for this class of hydrogen-bonded glass forming liquids.Comment: 4 pages, 4 figure
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