1,063 research outputs found
Exoplanet Transit Variability: Bow Shocks and Winds Around HD 189733b
By analogy with the solar system, it is believed that stellar winds will form
bow shocks around exoplanets. For hot Jupiters the bow shock will not form
directly between the planet and the star, causing an asymmetric distribution of
mass around the exoplanet and hence an asymmetric transit. As the planet orbits
thorough varying wind conditions, the strength and geometry of its bow shock
will change, thus producing transits of varying shape. We model this process
using magnetic maps of HD 189733 taken one year apart, coupled with a 3D
stellar wind model, to determine the local stellar wind conditions throughout
the orbital path of the planet. We predict the time-varying geometry and
density of the bow shock that forms around the magnetosphere of the planet and
simulate transit light curves. Depending on the nature of the stellar magnetic
field, and hence its wind, we find that both the transit duration and ingress
time can vary when compared to optical light curves. We conclude that
consecutive near-UV transit light curves may vary significantly and can
therefore provide an insight into the structure and evolution of the stellar
wind.Comment: 9 Pages, 7 figures. Accepted for publication in Monthly Notices of
The Royal Astronomical Societ
M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets
We perform three-dimensional numerical simulations of stellar winds of
early-M dwarf stars. Our simulations incorporate observationally reconstructed
large-scale surface magnetic maps, suggesting that the complexity of the
magnetic field can play an important role in the angular momentum evolution of
the star, possibly explaining the large distribution of periods in field dM
stars, as reported in recent works. In spite of the diversity of the magnetic
field topologies among the stars in our sample, we find that stellar wind
flowing near the (rotational) equatorial plane carries most of the stellar
angular momentum, but there is no preferred colatitude contributing to mass
loss, as the mass flux is maximum at different colatitudes for different stars.
We find that more non-axisymmetric magnetic fields result in more asymmetric
mass fluxes and wind total pressures (defined as the sum of
thermal, magnetic and ram pressures). Because planetary magnetospheric sizes
are set by pressure equilibrium between the planet's magnetic field and , variations of up to a factor of in (as found in the
case of a planet orbiting at several stellar radii away from the star) lead to
variations in magnetospheric radii of about 20 percent along the planetary
orbital path. In analogy to the flux of cosmic rays that impact the Earth,
which is inversely modulated with the non-axisymmetric component of the total
open solar magnetic flux, we conclude that planets orbiting M dwarf stars like
DT~Vir, DS~Leo and GJ~182, which have significant non-axisymmetric field
components, should be the more efficiently shielded from galactic cosmic rays,
even if the planets lack a protective thick atmosphere/large magnetosphere of
their own.Comment: 16 pages, 9 figures, to appear in MNRA
Isolation of 10 cyclosporine metabolites from human bile
Ten metabolites of cyclosporine were isolated from the ethyl ether extract of bile from four liver transplant patients receiving cyclosporine. Two of the metabolites were unique and previously unidentified. Liquid-liquid partitioning into diethyl ether with subsequent defatting with n-hexane was used for the initial extraction form bile. Separation of the individual metabolites (A-J) was performed using a Sephadex LH-20 column and a gradient high performance liquid chromatographic method. The molecular weights of the isolated metabolites were determined by fast atom bombardment/mass spectrometry. Gas chromatography with mass spectrometic amino acid analysis was also used to identify the amino acid composition and the hydroxylation position of metabolites A, B, C, D, and G. Proton nuclear magnetic resonance spectra were utilized to disinguish the chemical shifts of N-CH3 singlets and NH doublets of metabolites A, B, C, and D. Metabolites A, E, F, H, I, and J were reported previously in human urine and animal bile. Metabolites C and D are dihydroxylated compounds which cannot be clearly described as previously isolated compounds. Metabolites B and G are novel metabolites with a mass fragment which corresponded to a loss of 131 Da from the protonated molecular ion (MH+) in the fast atom bombardment/mass spectrometry, suggesting that the double bond in amino acid 1 has been modified. Metabolites B and G were primarily isolated from the bile of one of the liver transplant patients which contained abnormally high concentrations of these two metabolites. The method described is an efficient procedure for isolating milligram quantities of the major metabolites with greater than 95% purity
Considerações Sobre o Bioetanol Lignocelulósico para Subsidiar a Elaboração de Conteúdo da Árvore do Conhecimento Agroenergia.
De acordo com a previsão da Agência Internacional de Energia (AIE) até o ano de 2030, os biocombustíveis representarão cerca de 7% do combustível utilizado no transporte, sendo a União Européia, os Estados Unidos e o Brasil os principais produtores e consumidores. Esse crescimento no mercado internacional é esperado devido ao aumento do preço do petróleo e, também porque os países desenvolvidos que assinaram o Protocolo de Kyoto se comprometeram a reduzir suas emissões de gases poluentes (BRASIL, 2005). Os constantes conflitos envolvendo os países do Oriente Médio, que estão nas regiões das reservas de petróleo, causam instabilidade ao suprimento e oscilações nos preços dos combustíveis fósseis, forçando vários países a buscarem alternativas que possibilitem reduzir a dependência em relação às importações desse produto. Todos esses fatores, cuja importância varia de país para país, vêm criando oportunidades para a viabilização econômica de novas fontes de energia de biomassa. O uso do etanol, biodiesel, carvão vegetal, biogás e energia obtida a partir de resíduos do agronegócio desperta interesse crescente em muitos países, não restando dúvidas de que ocupará posição de destaque na economia mundial no futuro próximo. O bioetanol pode ser obtido de diferentes matérias-primas, cada qual com um custo de produção e um valor de venda.bitstream/item/17345/1/doc95.pd
Considerações sobre biodiesel como biocombustível alternativo ao diesel.
Biodiesel é definido como o produto da reação de gordura animal ou vegetal com álcool (ou transesterificação). Tecnicamente podemos dizer que dos triglicerídeos presentes nessas matérias graxas (óleos vegetais ou animais), ésteres monoalquílicos (como os ésteres de etila e de metila) são produzidos pela reação com um álcool primário (etanol ou metanol) em meio preferencialmente alcalino. Esses ésteres também podem ser obtidos a partir de ácidos graxos livres, mas, nesse caso, a reação é de esterificação, e sua condução deve ser em meio preferencialmente ácido. As principais matérias-primas para a produção nacional do biodiesel são: soja, milho, girassol, amendoim, algodão, canola, mamona, babaçu, palma (dendê) e macaúba, entre outras oleaginosas existentes no país. O combustível também pode ser obtido a partir de óleos residuais e de gorduras animais. Além de ser uma tecnologia limpa, o emprego do biodiesel no óleo diesel de petróleo polui menos o meio ambiente, pode reduzir a dependência brasileira das importações de petróleo e trazer vantagens econômicas, pois sua produção e o cultivo das matérias-primas podem criar milhares de novos empregos, inclusive na agricultura familiar, principalmente nas regiões mais pobres do Brasil.bitstream/item/17275/1/doc93-1.pd
Indicações de aspecto tecnológico sobre o bioetanol de matéria-prima amilácea.
A matriz energética mundial ainda é fortemente inclinada para as fontes de carbono fóssil, com participação total de 80%, sendo 36% de petróleo, 23% de carvão mineral e 21% de gás natural. São muitos os estudos que apontam o esgotamento das fontes de energia fóssil para as próximas quatro a cinco décadas, destacando a necessidade de buscar outras fontes alternativas de energia.bitstream/item/17276/1/doc94-1.pd
Principal infinity-bundles - General theory
The theory of principal bundles makes sense in any infinity-topos, such as
that of topological, of smooth, or of otherwise geometric
infinity-groupoids/infinity-stacks, and more generally in slices of these. It
provides a natural geometric model for structured higher nonabelian cohomology
and controls general fiber bundles in terms of associated bundles. For suitable
choices of structure infinity-group G these G-principal infinity-bundles
reproduce the theories of ordinary principal bundles, of bundle
gerbes/principal 2-bundles and of bundle 2-gerbes and generalize these to their
further higher and equivariant analogs. The induced associated infinity-bundles
subsume the notions of gerbes and higher gerbes in the literature.
We discuss here this general theory of principal infinity-bundles, intimately
related to the axioms of Giraud, Toen-Vezzosi, Rezk and Lurie that characterize
infinity-toposes. We show a natural equivalence between principal
infinity-bundles and intrinsic nonabelian cocycles, implying the classification
of principal infinity-bundles by nonabelian sheaf hyper-cohomology. We observe
that the theory of geometric fiber infinity-bundles associated to principal
infinity-bundles subsumes a theory of infinity-gerbes and of twisted
infinity-bundles, with twists deriving from local coefficient infinity-bundles,
which we define, relate to extensions of principal infinity-bundles and show to
be classified by a corresponding notion of twisted cohomology, identified with
the cohomology of a corresponding slice infinity-topos.
In a companion article [NSSb] we discuss explicit presentations of this
theory in categories of simplicial (pre)sheaves by hyper-Cech cohomology and by
simplicial weakly-principal bundles; and in [NSSc] we discuss various examples
and applications of the theory.Comment: 46 pages, published versio
Mass Accretion onto T Tauri Stars
It is now accepted that accretion onto classical T Tauri stars is controlled
by the stellar magnetosphere, yet to date most accretion models have assumed
that their magnetic fields are dipolar. By considering a simple steady state
accretion model with both dipolar and complex magnetic fields we find a
correlation between mass accretion rate and stellar mass of the form , with our results consistent within observed
scatter. For any particular stellar mass there can be several orders of
magnitude difference in the mass accretion rate, with accretion filling factors
of a few percent. We demonstrate that the field geometry has a significant
effect in controlling the location and distribution of hot spots, formed on the
stellar surface from the high velocity impact of accreting material. We find
that hot spots are often at mid to low latitudes, in contrast to what is
expected for accretion to dipolar fields, and that particularly for higher mass
stars, the accretion flow is predominantly carried by open field lines.Comment: 17 pages, 10 figures, accepted for publication by MNRA
Improving binding affinity prediction by using a rule-based model with physical-chemical and structural descriptors of the nano-environment for protein-ligand interactions.
In order to improve binding affinity prediction, we developed a new scoring function, named STINGSF, derived from physical-chemical and structural features that describe the protein-ligand interaction nano-environment of experimentally determined structures.C.047
Electrostatic potential at the alpha carbon atoms along the alpha helices and beta strands.
We present here analysis of pre-calculated values for the electrostatic potential at the alpha carbons, previously stored in the STING_RDB.PABMB
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