10,128 research outputs found
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
Abundance patterns in early-type galaxies: is there a 'knee' in the [Fe/H] vs. [alpha/Fe] relation?
Early-type galaxies (ETGs) are known to be enhanced in alpha elements, in
accordance with their old ages and short formation timescales. In this
contribution we aim to resolve the enrichment histories of ETGs. This means we
study the abundance of Fe ([Fe/H]) and the alpha-element groups ([alpha/Fe])
separately for stars older than 9.5 Gyr ([Fe/H]o, [alpha/Fe]o) and for stars
between 1.5 and 9.5 Gyr ([Fe/H]i, [alpha/Fe]i). Through extensive simulation we
show that we can indeed recover the enrichment history per galaxy. We then
analyze a spectroscopic sample of 2286 early-type galaxies from the SDSS
selected to be ETGs. We separate out those galaxies for which the abundance of
iron in stars grows throughout the lifetime of the galaxy, i.e. in which
[Fe/H]o < [Fe/H]i. We confirm earlier work where the [Fe/H] and [alpha/Fe]
parameters are correlated with the mass and velocity dispersion of ETGs. We
emphasize that the strongest relation is between [alpha/Fe] and age. This
relation falls into two regimes, one with a steep slope for old galaxies and
one with a shallow slope for younger ETGs. The vast majority of ETGs in our
sample do not show the 'knee' in the plot of [Fe/H] vs. [alpha/Fe] commonly
observed in local group galaxies. This implies that for the vast majority of
ETGs, the stars younger than 9.5 Gyrs are likely to have been accreted or
formed from accreted gas. The properties of the intermediate-age stars in
accretion-dominated ETGs indicate that mass growth through late (minor) mergers
in ETGs is dominated by galaxies with low [Fe/H] and low [alpha/Fe]. The method
of reconstructing the stellar enrichment histories of ETGs introduced in this
paper promises to constrain the star formation and mass assembly histories of
large samples of galaxies in a unique way.Comment: 22 pages, 25 figures, accepted for publication by A&
A rapid and simple method for determination of 5-hydroxytryptophan in dietary supplements by capillary electrophoresis
A rapid and simple capillary electrophoresis (CE) method was developed to determine 5-hydroxytryptophan (5-HTP) in samples of commercial dietary supplements. The optimized background electrolyte (BGE) was composed by 20 mmol L-1 sodium phosphate (pH 10) and 0.2 mmol L-1 cetyltrimethylammonium bromide (CTAB) for electroosmotic flow inversion. The limits of detection (LOD) and quantification (LOQ) for 5-HTP were 3.1 and 10.1 µmol L-1, respectively. The analytical curve demonstrated linearity over a concentration range of 0-500 µmol L-1 with a correlation coefficient (R2) of 0.9995. The intraday instrumental precision (repeatability) as relative standard deviation (RSD) in terms of peak area and migration time of the 5-HTP were 2.2 and 1.9% (n = 8), respectively. The CE method was applied to the analysis of four different samples of commercial dietary supplements and the RSD (n = 3) for the determinations ranged from 2 to 3%. The accuracy of the method was evaluated comparing the measured 5-HTP concentrations to those obtained by a high performance liquid chromatography (HPLC) method. The relative error ranged from 0 to 5.9% (n = 3) and no significant differences between the concentrations were observed at a confidence level of 95%254783787Neste trabalho é apresentado o desenvolvimento de um método rápido e simples, empregando eletroforese capilar, para determinação de 5-hidroxitriptofano (5-HTP) em amostras de suplementos alimentares. O eletrólito de corrida utilizado foi constituído por 20 mmol L-1 de fosfato de sódio (pH 10) e 0,2 mmol L-1 de brometo de cetiltrimetilamônio (CTAB), empregado como inversor de fluxo eletrosmótico. Foram obtidos limites de detecção e quantificação de 3,1 e 10,1 µmol L-1, respectivamente. A curva analítica obtida, para concentrações do analito entre 0-500 µmol L-1, apresentou linearidade com coeficiente de correlação linear (R2) de 0,9995. A precisão instrumental intra-dia (repetibilidade), expressa em desvio padrão relativo (RSD), para a área de pico e tempo de migração do 5-HTP foram de 2,2 e 1,9% (n = 8), respectivamente. O método eletroforético foi empregado na análise de quatro diferentes amostras comerciais de suplementos alimentares e o RSD (n = 3) para as determinações variaram de 2 a 3%. A exatidão do método foi avaliada pela comparação das concentrações de 5-HTP obtidas pelo método proposto e por cromatografia líquida de alta eficiência (HPLC). Os erros relativos variaram entre 0 e 5,9% e não foram observadas diferenças significativas entre as concentrações, ao nível de 95% de confianç
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
Análise da diversidade genética de variedades tradicionais de feijoeiro comum utilizando marcadores microssatélites.
No Brasil, foi estabelecida, a partir da década de 70, uma rede de pesquisa com ênfase na conservação e uso dos recursos genéticos do feijoeiro comum. O banco de germoplasma da Embrapa Arroz e Feijão detém aproximadamente 17.345 acessos, dos quais 4.325 são variedades tradicionais (VTs). Esses acessos representam uma rica fonte de genes que conferem adaptação a diferentes ambientes, resistência a doenças e propriedades agronômicas diferenciadas que podem ser exploradas por meio de técnicas moleculares que fornecem medidas bastante eficientes e diretas da variabilidade genética existente dentro e entre os acessos. Esse estudo teve como objetivo a avaliação da variabilidade genética de VTs de feijoeiro comum utilizando marcadores microssatélites (SSRs).Pôster - graduação
Evaluation of mineral content in maize under flooding.
This study examined the effects of plant mineral content on different cycles of recurrent selection of the flood-tolerant, open-pollinated maize variety BRS 4154 - "Saracura", under soil flooding. Experiments with the main treatments flooded or unflooded were conducted in Sete Lagoas, MG - Brazil. Samples of the cycles 1, 5, 9 and 15 were sown in a randomized block design. The open-pollinated variety BR 107 and single-cross hybrid BRS 1010 were used as flood-susceptible controls. The stress caused by water excess in the soil reduced the nitrogen content in the cycles 5 and 9, and calcium in cycle 15; but increased potassium in cycle 1. However, it did not significantly influence the content of phosphorus, magnesium, sulfur, zinc, and copper. Additionally, recurrent selection under flooding diminished potassium and calcium content along the cycles
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