126 research outputs found
Dynamically coupled kinetic chemistry in brown dwarf atmospheres I. Performing global scale kinetic modelling
The atmospheres of brown dwarfs have been long observed to exhibit a
multitude of non-equilibrium chemical signatures and spectral variability
across the L, T and Y spectral types. We aim to investigate the link between
the large-scale 3D atmospheric dynamics and time-dependent chemistry in the
brown dwarf regime, and to assess its impact on spectral variability. We couple
the miniature kinetic chemistry module `mini-chem' to the Exo-FMS general
circulation model (GCM). We then perform a series of idealised brown dwarf
regime atmospheric models to investigate the dynamical 3D chemical structures
produced by our simulations. The GCM output is post-processed using a 3D
radiative-transfer model to investigate hemisphere-dependent spectral
signatures and rotational variability. Our results show the expected strong
non-equilibrium chemical behaviour brought on by vertical mixing as well as
global spacial variations due to zonal flows. Chemical species are generally
globally homogenised, showing variations of 10\% or less, dependent on
pressure level, and follow the dynamical structures present in the atmosphere.
However, we find localised storm regions and eddies can show higher contrasts,
up to 100\%, in mixing ratio compared to the background global mean. This
initial study represents another step in understanding the connection between
three-dimensional atmospheric flows in brown dwarfs and their rich chemical
inventories.Comment: MNRAS Accepted: 5 June 202
A Mini-Chemical Scheme with Net Reactions for 3D GCMs II. 3D thermochemical modelling of WASP-39b and HD 189733b
The chemical inventory of hot Jupiter (HJ) exoplanets atmospheres continue to
be observed by various ground and space based instruments in increasing detail
and precision. It is expected that some HJs will exhibit strong non-equilibrium
chemistry characteristics in their atmospheres, which might be inferred from
spectral observations. We aim to model the three dimensional thermochemical
non-equilibrium chemistry in the atmospheres of the HJs WASP-39b and HD
189733b. We couple a lightweight, reduced chemical network `mini-chem' that
utilises net reaction rate tables to the Exo-FMS General Circulation Model
(GCM). We perform GCM models of the exoplanets WASP-39b and HD 189733b as case
studies of the coupled mini-chem scheme. The GCM results are then
post-processed using the 3D radiative-transfer model gCMCRT to produce
transmission and emission spectra to assess the impact of non-equilibrium
chemistry on their observable properties. Both simulations show significant
departures from chemical equilibrium (CE) due to the dynamical motions of the
atmosphere. The spacial distribution of species generally follows closely the
dynamical features of the atmosphere rather than the temperature field. Each
molecular species exhibits a different quench level in the simulations, also
dependent on the latitude of the planet. Major differences are seen in the
transmission and emission spectral features between the CE and kinetic models.
Our simulations indicate that considering the 3D kinetic chemical structures of
HJ atmospheres has an important impact on physical interpretation of
observational data. Drawing bulk atmospheric parameters from fitting feature
strengths may lead to inaccurate interpretation of chemical conditions in the
atmosphere of HJs. Our open source mini-chem module is simple to couple with
contemporary HJ GCM models without substantially increasing required
computational resources.Comment: A&A Accepted 17 Feb 202
Simulating gas giant exoplanet atmospheres with Exo-FMS: Comparing semi-grey, picket fence and correlated-k radiative-transfer schemes
Radiative-transfer (RT) is a fundamental part of modelling exoplanet
atmospheres with general circulation models (GCMs). An accurate RT scheme is
required for estimates of the atmospheric energy transport and for gaining
physical insight from model spectra. We implement three RT schemes for Exo-FMS:
semi-grey, non-grey `picket fence', and real gas with correlated-k. We
benchmark the Exo-FMS GCM using these RT schemes to hot Jupiter simulation
results from the literature. We perform a HD 209458b-like simulation with the
three schemes and compare their results. These simulations are then
post-processed to compare their observable differences. The semi-grey scheme
results show qualitative agreement with previous studies in line with
variations seen between GCM models. The real gas model reproduces well the
temperature and dynamical structures from other studies. After post-processing
our non-grey picket fence scheme compares very favourably with the real gas
model, producing similar transmission spectra, emission spectra and phase curve
behaviours. Exo-FMS is able to reliably reproduce the essential features of
contemporary GCM models in the hot gas giant regime. Our results suggest the
picket fence approach offers a simple way to improve upon RT realism beyond
semi-grey schemes.Comment: MNRAS accepted 22 June 2021 - V2, typos fixe
A detailed analysis of the HD 73526 2:1 resonant planetary system
We present six years of new radial velocity data from the Anglo-Australian and Magellan Telescopes on the HD 73526 2:1 resonant planetary system. We investigate both Keplerian and dynamical ( interacting) fits to these data, yielding four possible configurations for the system. The new data now show that both resonance angles are librating, with amplitudes of 40 degrees and 60 degrees, respectively. We then perform long-term dynamical stability tests to differentiate these solutions, which only differ significantly in the masses of the planets. We show that while there is no clearly preferred system inclination, the dynamical fit with i = 90 degrees provides the best combination of goodness-of-fit and long-term dynamical stability.Peer reviewe
Global intercomparison of polyurethane foam passive air samplers evaluating sources of variability in SVOC measurements
Polyurethane foam passive air samplers (PUF-PAS) are the most common type of passive air sampler used for a range of semi-volatile organic compounds (SVOCs), including regulated persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs), and emerging contaminants (e.g., novel flame retardants, phthalates, current-use pesticides). Data from PUF-PAS are key indicators of effectiveness of global regulatory actions on SVOCs, such as the Global Monitoring Plan of the Stockholm Convention on Persistent Organic Pollutants. While most PUF-PAS use similar double-dome metal shielding, there is no standardized dome size, shape, or deployment configuration, with many different PUF-PAS designs used in regional and global monitoring. Yet, no information is available on the comparability of data from studies using different PUF-PAS designs. We brought together 12 types of PUF-PAS used by different research groups around the world and deployed them in a multi-part intercomparison to evaluate the vari-ability in reported concentrations introduced by different elements of PAS monitoring. PUF-PAS were deployed for 3 months in outdoor air in Kjeller, Norway in 2015-2016 in three phases to capture (1) the influence of sampler design on data comparability, (2) the influence of analytical variability when samplers are analyzed at different laboratories, and (3) the overall variability in global monitoring data introduced by differences in sampler configurations and analytical methods. Results indicate that while differences in sampler design (in particular, the spacing between the upper and lower sampler bowls) account for up to 50 % differences in masses collected by samplers, the variability introduced by analysis in different laboratories far exceeds this amount, resulting in differences spanning orders of magnitude for POPs and PAHs. The high level of variability due to analysis in different laboratories indicates that current SVOC air sampling data (i.e., not just for PUF-PAS but likely also for active air sampling) are not directly comparable between laboratories/monitoring programs. To support on-going efforts to mobilize more SVOC data to contribute to effectiveness evaluation, intercalibration exercises to account for uncertainties in air sampling, repeated at regular intervals, must be established to ensure analytical comparability and avoid biases in global-scale assessments of SVOCs in air caused by differences in laboratory performance
Magnetic Behavior of Surface Nanostructured 50-nm Nickel Thin Films
Thermally evaporated 50-nm nickel thin films coated on borosilicate glass substrates were nanostructured by excimer laser (0.5 J/cm2, single shot), DC electric field (up to 2 kV/cm) and trench-template assisted technique. Nanoparticle arrays (anisotropic growth features) have been observed to form in the direction of electric field for DC electric field treatment case and ruptured thin film (isotropic growth features) growth for excimer laser treatment case. For trench-template assisted technique; nanowires (70–150 nm diameters) have grown along the length of trench template. Coercive field and saturation magnetization are observed to be strongly dependent on nanostructuring techniques
Global Expression Analysis Revealed Novel Gender-Specific Gene Expression Features in the Blood Fluke Parasite Schistosoma japonicum
BACKGROUND: Schistosoma japonicum is one of the remarkable Platyhelminths that are endemic in China and Southeast Asian countries. The parasite is dioecious and can reside inside the host for many years. Rapid reproduction by producing large number of eggs and count-react host anti-parasite responses are the strategies that benefit long term survival of the parasite. Praziquantel is currently the only drug that is effective against the worms. Development of novel antiparasite reagents and immune-prevention measures rely on the deciphering of parasite biology. The decoding of the genomic sequence of the parasite has made it possible to dissect the functions of genes that govern the development of the parasite. In this study, the polyadenylated transcripts from male and female S. japonicum were isolated for deep sequencing and the sequences were systematically analysed. RESULTS: First, the number of genes actively expressed in the two sexes of S. japonicum was similar, but around 50% of genes were biased to either male or female in expression. Secondly, it was, at the first time, found that more than 50% of the coding region of the genome was transcribed from both strands. Among them, 65% of the genes had sense and their cognate antisense transcripts co-expressed, whereas 35% had inverse relationship between sense and antisense transcript abundance. Further, based on gene ontological analysis, more than 2,000 genes were functionally categorized and biological pathways that are differentially functional in male or female parasites were elucidated. CONCLUSIONS: Male and female schistosomal parasites differ in gene expression patterns, many metabolic and biological pathways have been identified in this study and genes differentially expressed in gender specific manner were presented. Importantly, more than 50% of the coding regions of the S. japonicum genome transcribed from both strands, antisense RNA-mediated gene regulation might play a critical role in the parasite biology
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