1,543 research outputs found
Observability of hydrogen-rich exospheres in Earth-like exoplanets
(Abridged) The existence of an extended neutral hydrogen exosphere around
small planets can be used as an evidence for the presence of water in their
lower atmosphere but, to date, such feature has not been securely detected in
rocky exoplanets. Planetary exospheres can be observed using transit
spectroscopy of the Lyman- line, which is limited mainly by
interstellar medium absorption in the core of the line, and airglow
contamination from the geocorona when using low-orbit space telescopes. Our
objective is to assess the detectability of the neutral hydrogen exosphere of
an Earth-like planet transiting a nearby M dwarf using Lyman-
spectroscopy and provide the necessary strategies to inform future
observations. The spatial distribution in the upper atmosphere is provided by
an empirical model of the geocorona, and we assume a velocity distribution
based on radiative pressure as the main driver in shaping the exosphere. We
compute the excess absorption in the stellar Lyman- line while in
transit, and use realistic estimates of the uncertainties involved in
observations to determine the observability of the signal. We found that the
signal in Lyman- of the exosphere of an Earth-like exoplanet transiting
M dwarfs with radii between 0.1 and 0.6 R produces an excess absorption
between 50 and 600 ppm. The Lyman- flux of stars decays exponentially
with distance because of interstellar medium absorption, which is the main
observability limitation. Other limits are related to the stellar radial
velocity and instrumental setup. The excess absorption in Lyman- is
observable using LUVOIR/LUMOS in M dwarfs up to a distance of 15 pc. The
analysis of noise-injected data suggests that it would be possible to detect
the exosphere of an Earth-like planet transiting TRAPPIST-1 within 20 transits.Comment: 12 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
Observing atmospheric escape in sub-Jovian worlds with JWST
Hydrodynamic atmospheric escape is considered an important process that
shapes the evolution of sub-Jovian exoplanets, particularly those with short
orbital periods. The metastable He line in the near-infrared at m
is a reliable tracer of atmospheric escape in hot exoplanets, with the
advantage of being observable from the ground. However, observing escaping He
in sub-Jovian planets has remained challenging due to the systematic effects
and telluric contamination present in ground-based data. With the successful
launch and operations of JWST, we now have access to extremely stable
high-precision near-infrared spectrographs in space. Here we predict the
observability of metastable He with JWST in two representative and previously
well-studied warm Neptunes, GJ 436 b (, ) and GJ 1214 b (, ). Our simulated JWST observations for GJ 436 b demonstrate that
a single transit with NIRSpec/G140H is sensitive to mass loss rates that are
two orders of magnitude lower than what is detectable from the ground. Our
exercise for GJ 1214 b show that the best configuration to observe the
relatively weak outflows of warm Neptunes with JWST is with NIRSpec/G140H, and
that NIRSpec/G140M and NIRISS/SOSS are less optimal. Since none of these
instrument configurations can spectrally resolve the planetary absorption, we
conclude that the 1D isothermal Parker-wind approximation may not be sufficient
for interpreting such observations. More sophisticated models are critical for
breaking the degeneracy between outflow temperature and mass-loss rate for JWST
measurements of metastable He.Comment: 14 pages, 7 figures, under review at AAS Journals; this version
follows the first round of revision. Feedback from the community is welcom
Evolution of helium triplet transits of close-in gas giants orbiting K-dwarfs
Atmospheric escape in exoplanets has traditionally been observed using
hydrogen Lyman- and H- transmission spectroscopy, but more
recent detections have utilised the metastable helium triplet at 1083nm.
Since this feature is accessible from the ground, it offers new possibilities
for studying atmospheric escape. Our goal is to understand how the
observability of escaping helium evolves during the lifetime of a highly
irradiated gas giant. We extend our previous work on 1-D self-consistent
hydrodynamic escape from hydrogen-only atmospheres as a function of planetary
evolution to the first evolution-focused study of escaping hydrogen-helium
atmospheres. Additionally, using these novel models we perform helium triplet
transmission spectroscopy. We adapt our previous hydrodynamic escape model to
now account for both hydrogen and helium heating and cooling processes and
simultaneously solve for the population of helium in the triplet state. To
account for the planetary evolution, we utilise evolving predictions of
planetary radii for a close-in 0.3 gas giant and its received
stellar flux in X-ray, hard and soft EUV, and mid-UV wavelength bins assuming a
K dwarf stellar host. We find that the helium triplet signature diminishes with
evolution. Our models suggest that young (~Myr), close-in gas
giants ( to ) should produce helium 1083nm transit
absorptions of or , for a slow or fast-rotating K dwarf,
respectively, assuming a 2 helium abundance.Comment: 20 pages, 13 figures, 4 tables; accepted for publication in MNRA
Constraining the evolution of stellar rotation using solar twins
The stellar Rotation Age relation is commonly considered as a useful
tool to derive reliable ages for Sun-like stars. However, in the light of
\kepler\ data, the presence of apparently old and fast rotators that do not
obey the usual gyrochronology relations led to the hypothesis of weakened
magnetic breaking in some stars. In this letter, we constrain the solar
rotation evolutionary track using solar twins. Predicted rotational periods as
a function of mass, age, [Fe/H] and given critical Rossby number () were estimated for the entire rotational sample. Our analysis favors
the smooth rotational evolution scenario and suggests that, if the magnetic
weakened breaking scenario takes place at all, it should arise after or ages 5.3 Gyr (at 95 confidence level).Comment: 5 pages, 3 figures, accepted for publication in MNRA
Strategies for Efficient Expression of Heterologous Monosaccharide Transporters in Saccharomyces cerevisiae
ABSTRACT: In previous work, we developed a Saccharomyces cerevisiae strain (DLG-K1) lacking the main monosaccharide transporters (hxt-null) and displaying high xylose reductase, xylitol dehydrogenase and xylulokinase activities. This strain proved to be a useful chassis strain to study new glucose/xylose transporters, as SsXUT1 from Scheffersomyces stipitis. Proteins with high amino acid sequence similarity (78-80%) to SsXUT1 were identified from Spathaspora passalidarum and Spathaspora arborariae genomes. The characterization of these putative transporter genes (SpXUT1 and SaXUT1, respectively) was performed in the same chassis strain. Surprisingly, the cloned genes could not restore the ability to grow in several monosaccharides tested (including glucose and xylose), but after being grown in maltose, the uptake of C-14-glucose and C-14-xylose was detected. While SsXUT1 lacks lysine residues with high ubiquitinylation potential in its N-terminal domain and displays only one in its C-terminal domain, both SpXUT1 and SaXUT1 transporters have several such residues in their C-terminal domains. A truncated version of SpXUT1 gene, deprived of the respective 3 '-end, was cloned in DLG-K1 and allowed growth and fermentation in glucose or xylose. In another approach, two arrestins known to be involved in the ubiquitinylation and endocytosis of sugar transporters (ROD1 and ROG3) were knocked out, but only the rog3 mutant allowed a significant improvement of growth and fermentation in glucose when either of the XUT permeases were expressed. Therefore, for the efficient heterologous expression of monosaccharide (e.g., glucose/xylose) transporters in S. cerevisiae, we propose either the removal of lysines involved in ubiquitinylation and endocytosis or the use of chassis strains hampered in the specific mechanism of membrane protein turnover.info:eu-repo/semantics/publishedVersio
PROCESSOS HIDRO-EROSIVOS EM SOLOS DEGRADADOS EM RELEVO DE BAIXA DECLIVIDADE (HYDRO-EROSIVE PROCESSES IN DEGRADED SOILS ON GENTLE SLOPE)
<p>Muitas pesquisas conferem maior peso na alta declividade do terreno como fator decisivo no processo hidro-erosivo. Porém, foi avaliado que baixas declividades (~4º) já são suficientes para se iniciar o escoamento superficial. A pesquisa teve como objetivo fazer uma caracterização fÃsico-quÃmica de solo degradado, monitorar o seu potencial matricial e o processo de formação de escoamento em uma sub-bacia do rio Maranduba - Ubatuba/SP, em encosta com baixa declividade. O trabalho se baseou na instalação de parcelas de erosão em solo sem cobertura vegetal para analisar as perdas de solo e água, bem como as propriedades fÃsicas e quÃmicas do solo (Porosidade, textura, densidade, pH e matéria orgânica). As parcelas se localizam na parte intermediária de um morrote com encosta retilÃnea, esse sofreu alteração em sua morfologia original por meio de um corte de encosta (UTM: 0474211/7395934).  O solo do local é um Latossolo que apresenta o horizonte B exposto. Cerca de 6,9 t/ha de solo foram perdidos durante o monitoramento (01 agosto 2013-20 dezembro 2014) e mais de 5.354,7 m<sup>3</sup> de água foram escoados superficialmente. Salienta-se a fragilidade dos ambientes degradados de baixa declividade frente à s altas taxas de perdas de solo e água, que, no perÃodo de 17 meses de monitoramento e com chuvas dentro da normalidade para o municÃpio, totalizaram 63 dias com ocorrências de escoamento, em solos que tendem à saturação por perÃodos prolongados. Portanto, o transporte das partÃculas de solo superficialmente está atrelado à baixa drenagem do terreno e à perda da resistência do solo, corroborando em perÃodos longos de umidade antecedente, sendo este um dos fatores decisivos para se iniciar o escoamento superficial.</p
Processing and Properties of Plastic Lumber
Plastic residue can be processed into composites using wood flour, mineral fillers, plant or synthetic fibers to obtain plastic lumber, a substitute material for natural wood. The composition and processing conditions are largely responsible for the final characteristics of the plastic lumber. Factors such as density, particle size and moisture content in the material to be processed require extruders with specific technical characteristics, in order to reduce the residence time of the plastic inside the equipment, maintain a constant feed rate and ensure good degassing and homogenization of the components. The composites can be manufactured using single-screw, co- or counter-rotating conical or parallel twin-screw extruders. Plastic lumber exhibits different physical and mechanical properties from natural wood, including lower stiffness (elastic modulus) and superior weathering resistance
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