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 $\leq$ Teff $\leq$ 25000\,K, -0.5 $\leq$ log g $\leq$ 5.5, and 12 chemical mixtures covering 0.0017 $\leq$ Z $\leq$ 0.049 at both scaled-solar and $\alpha$-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 $\alpha$-enhanced mixtures for each scaled-solar iron abundance, to allow studies of the $\alpha$-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 $10^{-6}-10^{-5}$. Besides, BI electrodynamics may lead to a maximum increase of order $10\%-20\%$ 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