1,127 research outputs found
Titan Atmospheric Chemistry Revealed by Low-temperature N2-CH4 Plasma Discharge Experiments
Chemistry in Titan's N2-CH4 atmosphere produces complex organic aerosols. The
chemical processes and the resulting organic compounds are still far from
understood, although extensive observations, laboratory, and theoretical
simulations have greatly improved physical and chemical constraints on Titan's
atmosphere. Here, we conduct a series of Titan atmosphere simulation
experiments with N2-CH4 gas mixtures and investigate the effect of initial CH4
ratio, pressure, and flow rate on the production rates and composition of the
gas and solid products at a Titan relevant temperature (100 K) for the first
time. We find that the production rate of the gas and solid products increases
with increasing CH4 ratio. The nitrogen-containing species have much higher
yield than hydrocarbons in the gas products, and the N-to-C ratio of the solid
products appears to be the highest compared to previous plasma simulations with
the same CH4 ratio. The greater degree of nitrogen incorporation in the low
temperature simulation experiments suggests temperature may play an important
role in nitrogen incorporation in Titan's cold atmosphere. We also find that H2
is the dominant gas product and serves as an indicator of the production rate
of new organic molecules in the experiment, and that CH2NH may greatly
contribute to the incorporation of both carbon and nitrogen into the solid
particles. The pressure and flow rate affect the amount of time of the gas
mixture exposed to the energy source and therefore impact the N2-CH4 chemistry
initiated by the plasma discharge, emphasizing the influence of the energy flux
in Titan atmospheric chemistry.Comment: Accepted in ACS Earth and Space Chemistry, 6 figure
Optical Properties of Organic Haze Analogues in Water-rich Exoplanet Atmospheres Observable with JWST
JWST has begun its scientific mission, which includes the atmospheric
characterization of transiting exoplanets. Some of the first exoplanets to be
observed by JWST have equilibrium temperatures below 1000 K, which is a regime
where photochemical hazes are expected to form. The optical properties of these
hazes, which controls how they interact with light, are critical for
interpreting exoplanet observations, but relevant experimental data are not
available. Here we measure the density and optical properties of organic haze
analogues generated in water-rich exoplanet atmosphere experiments. We report
optical constants (0.4 to 28.6 {\mu}m) of organic haze analogues for current
and future observational and modeling efforts covering the entire wavelength
range of JWST instrumentation and a large part of Hubble. We use these optical
constants to generate hazy model atmospheric spectra. The synthetic spectra
show that differences in haze optical constants have a detectable effect on the
spectra, impacting our interpretation of exoplanet observations. This study
emphasizes the need to investigate the optical properties of hazes formed in
different exoplanet atmospheres, and establishes a practical procedure to
determine such properties.Comment: 4 figures, 1 Table, Published in Nature Astronom
Laboratory Simulations of Haze Formation in the Atmospheres of super-Earths and mini-Neptunes: Particle Color and Size Distribution
Super-Earths and mini-Neptunes are the most abundant types of planets among
the ~3500 confirmed exoplanets, and are expected to exhibit a wide variety of
atmospheric compositions. Recent transmission spectra of super-Earths and
mini-Neptunes have demonstrated the possibility that exoplanets have haze/cloud
layers at high altitudes in their atmospheres. However, the compositions, size
distributions, and optical properties of these particles in exoplanet
atmospheres are poorly understood. Here, we present the results of experimental
laboratory investigations of photochemical haze formation within a range of
planetary atmospheric conditions, as well as observations of the color and size
of produced haze particles. We find that atmospheric temperature and
metallicity strongly affect particle color and size, thus altering the
particles' optical properties (e.g., absorptivity, scattering, etc.); on a
larger scale, this affects the atmospheric and surface temperature of the
exoplanets, and their potential habitability. Our results provide constraints
on haze formation and particle properties that can serve as critical inputs for
exoplanet atmosphere modeling, and guide future observations of super-Earths
and mini-Neptunes with the Transiting Exoplanet Survey Satellite (TESS), the
James Webb Space Telescope (JWST), and the Wide-Field Infrared Survey Telescope
(WFIRST).Comment: 19 pages, 4 figures and 1 tabl
Longtintudinal asscociations of experience of adversity and socioeconomic disadvantage during childhood with labour force participation and exit in later adulthood
The Extending Working Lives (EWL) agenda seeks to sustain employment up to and beyond traditional retirement ages. This study examined the potential role of childhood factors in shaping labour force participation and exit among older adults, with a view to informing proactive interventions early in the life-course to enhance individuals’ future capacity for extending their working lives. Childhood adversity and socioeconomic disadvantage have previously been linked to ill-health across the life-span and sickness benefit in early adulthood. This study builds upon previous research by examining associations between childhood adversity and self-reported labour force participation among older adults (aged 55). Data was from the National Child Development Study – a prospective cohort of all English, Scottish, & Welsh births in one week in 1958. There was evidence for associations between childhood adversity and increased risk of permanent sickness at 55 years – which were largely sustained after adjustment for educational disengagement and adulthood factors (mental/physical health, qualifications, socioeconomic disadvantage). Specifically, children who were abused or neglected were more likely to be permanently sick at 55 years. In addition, among males, those in care, those experiencing illness in the home, and those experiencing two or more childhood adversities were more likely to be permanently sick at 55 years. Childhood factors were also associated with part-time employment and retirement at 55 years. Severe childhood adversities may represent important distal predictors of labour force exit at 55 years, particularly via permanent sickness. Notably, some adversities show associations among males only, which may inform interventions designed to extend working lives
Wearable devices can predict the outcome of standardized 6-minute walk tests in heart disease
Wrist-worn devices with heart rate monitoring have become increasingly popular. Although current guidelines advise to consider clinical symptoms and exercise tolerance during decision-making in heart disease, it remains unknown to which extent wearables can help to determine such functional capacity measures. In clinical settings, the 6-minute walk test has become a standardized diagnostic and prognostic marker. We aimed to explore, whether 6-minute walk distances can be predicted by wrist-worn devices in patients with different stages of mitral and aortic valve disease. A total of n = 107 sensor datasets with 1,019,748 min of recordings were analysed. Based on heart rate recordings and literature information, activity levels were determined and compared to results from a 6-minute walk test. The percentage of time spent in moderate activity was a predictor for the achievement of gender, age and body mass index-specific 6-minute walk distances (p < 0.001; R2 = 0.48). The uncertainty of these predictions is demonstrated
The impact of pregnancy on the pharmacokinetics of antiseizure medications:A systematic review and meta-analysis of data from 674 pregnancies
Objective: Increasing evidence suggests that the physiological changes of pregnancy may impact pharmacokinetics of antiseizure medications (ASM), and this may affect treatment outcomes. The aim of this study was to quantify the pregnancy impact on the ASM pharmacokinetics. Methods: A systematic literature search was conducted in PubMed/EMBASE in November 2022 and updated in August 2023 for studies comparing levels of ASM in the same individuals during pregnancy and in the preconception/postpartum period. Alteration ratios between the 3rd trimester and baseline were estimated. We also performed a random-effects meta-analysis calculating between-timepoint differences in mean differences (MDs) and 95% confidence intervals (95%CIs) for dose-adjusted plasma concentrations (C/D ratios). Study quality was assessed using the ClinPK guidelines. Results: A total of 65 studies investigating 15 ASMs in 674 pregnancies were included. The largest differences were reported for lamotrigine, oxcarbazepine and levetiracetam (alteration ratio 0.42, range 0.07–2.45, 0.42, range 0.08–0.82 and 0.52, range 0.04–2.77 respectively): accordingly, C/D levels were lower in the 3rd trimester for lamotrigine, levetiracetam and the main oxcarbazepine metabolite monohydroxycarbazepine (MD = -12.33 × 10−3, 95%CI = -16.08 to −8.58 × 10−3 (μg/mL)/(mg/day), p < 0.001, MD = -7.16 (μg/mL)/(mg/day), 95%CI = -9.96 to −4.36, p < 0.001, and MD = -4.87 (μg/mL)/(mg/day), 95%CI = -9.39 to −0.35, p = 0.035, respectively), but not for oxcarbazepine (MD = 1.16 × 10−3 (μg/mL)/(mg/day), 95%CI = -2.55 to 0.24 × 10−3, p = 0.10). The quality of studies was acceptable with an average rating score of 11.5. Conclusions: Data for lamotrigine, oxcarbazepine (and monohydroxycarbazepine) and levetiracetam demonstrate major changes in pharmacokinetics during pregnancy, suggesting the importance of therapeutic drug monitoring to assist clinicians in optimizing treatment outcomes.</p
The impact of pregnancy on the pharmacokinetics of antiseizure medications:A systematic review and meta-analysis of data from 674 pregnancies
Objective: Increasing evidence suggests that the physiological changes of pregnancy may impact pharmacokinetics of antiseizure medications (ASM), and this may affect treatment outcomes. The aim of this study was to quantify the pregnancy impact on the ASM pharmacokinetics. Methods: A systematic literature search was conducted in PubMed/EMBASE in November 2022 and updated in August 2023 for studies comparing levels of ASM in the same individuals during pregnancy and in the preconception/postpartum period. Alteration ratios between the 3rd trimester and baseline were estimated. We also performed a random-effects meta-analysis calculating between-timepoint differences in mean differences (MDs) and 95% confidence intervals (95%CIs) for dose-adjusted plasma concentrations (C/D ratios). Study quality was assessed using the ClinPK guidelines. Results: A total of 65 studies investigating 15 ASMs in 674 pregnancies were included. The largest differences were reported for lamotrigine, oxcarbazepine and levetiracetam (alteration ratio 0.42, range 0.07–2.45, 0.42, range 0.08–0.82 and 0.52, range 0.04–2.77 respectively): accordingly, C/D levels were lower in the 3rd trimester for lamotrigine, levetiracetam and the main oxcarbazepine metabolite monohydroxycarbazepine (MD = -12.33 × 10−3, 95%CI = -16.08 to −8.58 × 10−3 (μg/mL)/(mg/day), p < 0.001, MD = -7.16 (μg/mL)/(mg/day), 95%CI = -9.96 to −4.36, p < 0.001, and MD = -4.87 (μg/mL)/(mg/day), 95%CI = -9.39 to −0.35, p = 0.035, respectively), but not for oxcarbazepine (MD = 1.16 × 10−3 (μg/mL)/(mg/day), 95%CI = -2.55 to 0.24 × 10−3, p = 0.10). The quality of studies was acceptable with an average rating score of 11.5. Conclusions: Data for lamotrigine, oxcarbazepine (and monohydroxycarbazepine) and levetiracetam demonstrate major changes in pharmacokinetics during pregnancy, suggesting the importance of therapeutic drug monitoring to assist clinicians in optimizing treatment outcomes.</p
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