1,271 research outputs found
Optical properties of potential condensates in exoplanetary atmospheres
The prevalence of clouds in currently observable exoplanetary atmospheres
motivates the compilation and calculation of their optical properties. First,
we present a new open-source Mie scattering code known as LX-MIE, which is able
to consider large size parameters () using a single computational
treatment. We validate LX-MIE against the classical MIEV0 code as well as
previous studies. Second, we embark on an expanded survey of the published
literature for both the real and imaginary components of the refractive indices
of 32 condensate species. As much as possible, we rely on experimental
measurements of the refractive indices and resort to obtaining the real from
the imaginary component (or vice versa), via the Kramers-Kronig relation, only
in the absence of data. We use these refractive indices as input for LX-MIE to
compute the absorption, scattering and extinction efficiencies of all 32
condensate species. Finally, we use a three-parameter function to provide
convenient fits to the shape of the extinction efficiency curve. We show that
the errors associated with these simple fits in the Wide Field Camera 3 (WFC3),
J, H and K wavebands are . These fits allow for the extinction cross
section or opacity of the condensate species to be easily included in retrieval
analyses of transmission spectra. We discuss prospects for future experimental
work. The compilation of the optical constants and LX-MIE are publicly
available as part of the open-source Exoclime Simulation Platform
(http://www.exoclime.org).Comment: accepted version; 15 pages, 5 figures, 3 table
The theory of transmission spectra revisited: a semi-analytical method for interpreting WFC3 data and an unresolved challenge
The computation of transmission spectra is a central ingredient in the study
of exoplanetary atmospheres. First, we revisit the theory of transmission
spectra, unifying ideas from several workers in the literature. Transmission
spectra lack an absolute normalization due to the a priori unknown value of a
reference transit radius, which is tied to an unknown reference pressure. We
show that there is a degeneracy between the uncertainty in the transit radius,
the assumed value of the reference pressure (typically set to 10 bar) and the
inferred value of the water abundance when interpreting a WFC3 transmission
spectrum. Second, we show that the transmission spectra of isothermal
atmospheres are nearly isobaric. We validate the isothermal, isobaric
analytical formula for the transmission spectrum against full numerical
calculations and show that the typical errors are ~0.1% (~10 ppm) within the
WFC3 range of wavelengths for temperatures of 1500 K (or higher). Third, we
generalize the previous expression for the transit radius to include a small
temperature gradient. Finally, we analyze the measured WFC3 transmission
spectrum of WASP-12b and demonstrate that we obtain consistent results with the
retrieval approach of Kreidberg et al. (2015) if the reference transit radius
and reference pressure are fixed to assumed values. The unknown functional
relationship between the reference transit radius and reference pressure
implies that it is the product of the water abundance and reference pressure
that is being retrieved from the data, and not just the water abundance alone.
This degeneracy leads to a limitation on how accurately we may extract
molecular abundances from transmission spectra using WFC3 data alone. Finally,
we compare our study to that of Griffith (2014) and discuss why the degeneracy
was missed in previous retrieval studies. [abridged]Comment: Accepted by MNRAS. 11 pages, 7 figures, 2 table
Analytical Models of Exoplanetary Atmospheres. IV. Improved Two-stream Radiative Transfer for the Treatment of Aerosols
We present a novel generalization of the two-stream method of radiative
transfer, which allows for the accurate treatment of radiative transfer in the
presence of strong infrared scattering by aerosols. We prove that this
generalization involves only a simple modification of the coupling coefficients
and transmission functions in the hemispheric two-stream method. This
modification originates from allowing the ratio of the first Eddington
coefficients to depart from unity. At the heart of the method is the fact that
this ratio may be computed once and for all over the entire range of values of
the single-scattering albedo and scattering asymmetry factor. We benchmark our
improved two-stream method by calculating the fraction of flux reflected by a
single atmospheric layer (the reflectivity) and comparing these calculations to
those performed using a 32-stream discrete-ordinates method. We further compare
our improved two-stream method to the two-stream source function (16 streams)
and delta-Eddington methods, demonstrating that it is often more accurate at
the order-of-magnitude level. Finally, we illustrate its accuracy using a toy
model of the early Martian atmosphere hosting a cloud layer composed of
carbon-dioxide ice particles. The simplicity of implementation and accuracy of
our improved two-stream method renders it suitable for implementation in
three-dimensional general circulation models. In other words, our improved
two-stream method has the ease of implementation of a standard two-stream
method, but the accuracy of a 32-stream method.Comment: Accepted by ApJS. 7 pages, 5 figure
Exoplanet Characterization by Multi-Observatory Transit Photometry with TESS and CHEOPS
Space-based photometric surveys have discovered large numbers of planets
transiting other stars, but these observe in a single band-pass and yield only
the planet radius, orbital period, and transit duration. Information on the
masses, compositions, and any atmospheres of these planets requires additional
observations from the ground or space. The Transiting Exoplanet Survey
Satellite (TESS) will yield thousands of planets around bright stars suitable
for such follow-up. In the absence of spectroscopy or spectrophotometry from
space, observations through the different pass-bands of multiple space
telescopes provide some spectral information useful for identifying false
positive signals, distinguishing between reflected light and thermal emission
from hot Jupiters, and detecting Rayleigh scattering by planetary atmospheres.
We calculated the expected difference in transit depths measured by the TESS
and Characterizing Exoplanets Satellites (CHEOPS) missions, which will be more
sensitive to redder and bluer optical wavelengths, respectively. The difference
due to companion or background stars is small (<3% for main sequence
companions) and likely to be negligible and undetectable. For only a few "hot"
Jupiters, can combined photometry disambiguate between the reflected and
thermal signals from planets. However, Rayleigh scattering by hazy atmospheres
with particles sizes near 0.04 m and at pressure altitudes above ~1 mbar
can be detected for ~100 transiting planets, assuming every planet has such an
atmosphere. Hazes with this characteristic particle size do not obscure
observations at longer (near-infrared) wavelengths; CHEOPS follow-up of
TESS-detected planets could thus identify candidates suitable for further study
with the James Webb Space Telescope.Comment: MNRAS, in pres
Clouds in the atmospheres of extrasolar planets. IV. On the scattering greenhouse effect of CO2 ice particles: Numerical radiative transfer studies
Owing to their wavelengths dependent absorption and scattering properties,
clouds have a strong impact on the climate of planetary atmospheres.
Especially, the potential greenhouse effect of CO2 ice clouds in the
atmospheres of terrestrial extrasolar planets is of particular interest because
it might influence the position and thus the extension of the outer boundary of
the classic habitable zone around main sequence stars.
We study the radiative effects of CO2 ice particles obtained by different
numerical treatments to solve the radiative transfer equation. The comparison
between the results of a high-order discrete ordinate method and simpler
two-stream approaches reveals large deviations in terms of a potential
scattering efficiency of the greenhouse effect. The two-stream methods
overestimate the transmitted and reflected radiation, thereby yielding a higher
scattering greenhouse effect. For the particular case of a cool M-type dwarf
the CO2 ice particles show no strong effective scattering greenhouse effect by
using the high-order discrete ordinate method, whereas a positive net
greenhouse effect was found in case of the two-stream radiative transfer
schemes. As a result, previous studies on the effects of CO2 ice clouds using
two-stream approximations overrated the atmospheric warming caused by the
scattering greenhouse effect. Consequently, the scattering greenhouse effect of
CO2 ice particles seems to be less effective than previously estimated. In
general, higher order radiative transfer methods are necessary to describe the
effects of CO2 ice clouds accurately as indicated by our numerical radiative
transfer studies.Comment: accepted for publication in A&
In Adults with Difficult Intubations, What Is a Gold Standard Method for Success?
The objective of this thesis is to analyze existing literature and guidelines for difficult intubations and provide clinical recommendations. This paper is a retrospective analysis of human trials focusing on preparation, medication, and tools in the field of emergency airway management. Techniques will be described and discussed. A large portion of intubations are described as difficult and have the potential to fail. Articles retrieved from databases PubMed, Medline, and PLOS ONE and the search engine Google Scholar were reviewed. Websites for the institutions of the American Society of Anesthesiologists and Difficult Airway Society were used in guidance. Currently, many guidelines exist for difficult intubation, and traditional bedside prediction has proven to be unreliable. Techniques such as preprocedural checklists, preoxygenation, proper positioning benefit all intubations. In addition, practicing the failed intubation protocol including a standardized tracheotomy procedure is recommended. The paralytic rocuronium may be superior to succinylcholine in critically ill or those likely to have difficult airways. Technologies such as video laryngoscope, supraglottic airway devices, and bougie-first intubation should be included in training and implemented in practice. The obese population may have specific changes to technique to reduce the risk of complications. Finally, cricoid pressure is theoretically beneficial but practically challenging to replicate and recommendations will be given regarding its implementation
Musil, Robert: Immobiliengeographie. : Märkte, Akteure, Politik
No abstract necessaryNo abstract necessar
Strategies for genetic transfer of an allele for resistance to Phytophthora megasperma f. sp. glycinea Kuan and Erwin in soybean [Glycine max (L.) Merr.]
The efficiency of backcrossing to transfer major genes for resistance to phytophthora stem and root rot, caused by Phytophthora megasperma f. sp. glycinea Kuan and Erwin, into susceptible soybean Glycine max (L.) Merr. cultivars is dependent on the number of backcrosses required to recover the desirable agronomic characteristics of the recurrent parent. The objective of this study was to determine in which backcross generation individual lines with Phytophthora resistance and yield equivalent to that of the recurrent parent can be selected, and in which backcross generation a group of random lines from the population have an average yield equivalent to that of the recurrent parent. The allele Rps(,1)(\u27k), for resistance to Phytophthora, was transferred from the cultivar Williams 82 to two susceptible recurrent parents, Cumberland and A78-123018. Thirty-six random resistant lines from each of five backcross generations were evaluated individually for agronomic traits. Bulks of the 36 lines of each backcross generation also were tested. The results indicated that, if the donor and recurrent parents differ in yield by 10% or less, a single cross is sufficient to develop a population from which a homozygous resistant line with a yield equal to that of the recurrent parent can be selected. Alternatively, the recurrent parent can be replaced by a bulk of random homozygous resistant lines after one backcross
- …