| 1. |
- Li, Longxiang, et al.
(författare)
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A spatiotemporal ensemble model to predict gross beta particulate radioactivity across the contiguous United States
- 2021
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Ingår i: Environment International. - : Elsevier BV. - 0160-4120. ; 156
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Tidskriftsartikel (refereegranskat)abstract
- Particulate radioactivity, a characteristic of particulate matter, is primarily determined by the abundance of radionuclides that are bound to airborne particulates. Exposure to high levels of particulate radioactivity has been associated with negative health outcomes. However, there are currently no spatially and temporally resolved particulate radioactivity data for exposure assessment purposes. We estimated the monthly distributions of gross beta particulate radioactivity across the contiguous United States from 2001 to 2017 with a spatial resolution of 32 km, via a multi-stage ensemble-based model. Particulate radioactivity was measured at 129 RadNet monitors across the contiguous U.S. In stage one, we built 264 base learning models using six methods, then selected nine base models that provide different predictions. In stage two, we used a non-negative geographically and temporally weighted regression method to aggregate the selected base learner predictions based on their local performance. The results of block cross-validation analysis suggested that the non-negative geographically and temporally weighted regression ensemble learning model outperformed all base learning model with the smallest rooted mean square error (0.094 mBq/m3). Our model provided an accurate estimation of particulate radioactivity, thus can be used in future health studies.
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| 2. |
- Li, Longxiang, et al.
(författare)
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Exposure to unconventional oil and gas development and all-cause mortality in Medicare beneficiaries
- 2022
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Ingår i: Nature Energy. - : Springer Science and Business Media LLC. - 2058-7546. ; 7:2, s. 177-185
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Tidskriftsartikel (refereegranskat)abstract
- Little is known about whether exposure to unconventional oil and gas development is associated with higher mortality risks in the elderly and whether related air pollutants are exposure pathways. We studied a cohort of 15,198,496 Medicare beneficiaries (136,215,059 person-years) in all major US unconventional exploration regions from 2001 to 2015. We gathered data from records of more than 2.5 million oil and gas wells. For each beneficiary’s ZIP code of residence and year in the cohort, we calculated a proximity-based and a downwind-based pollutant exposure. We analysed the data using two methods: a Cox proportional hazards model and a difference-in-differences design. We found evidence of a statistically significant higher mortality risk associated with living in proximity to and downwind of unconventional oil and gas wells. Our results suggest that primary air pollutants sourced from unconventional oil and gas exploration can be a major exposure pathway with adverse health effects in the elderly.
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| 3. |
- Li, Longxiang, et al.
(författare)
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Ratios between Radon Concentrations in Upstairs and Basements : A Study in the Northeastern and Midwestern United States
- 2022
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Ingår i: Environmental Science and Technology Letters. - : American Chemical Society (ACS). - 2328-8930. ; 9:2, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- Temporally resolved assessment of residential exposure to radon is essential for investigating radon's acute health effects. Recent studies have used large numbers of short-term radon measurements to model the spatiotemporal variations in radon concentrations. However, most short-term radon measurements in the northeastern and midwestern United States were conducted in the basements, which were less frequently occupied and had higher average radon concentrations than the upstairs spaces. Disproportionate usage of basement radon measurements in exposure assessment potentially introduces misclassifications. In an effort to mitigate the issue, we investigated the spatiotemporal gradients in ratios between the radon concentrations in the upstairs and basements (hereafter upstairs/basement ratio). Building-specific ratios were calculated on the basis of 10774 pairs of simultaneous short-term measurements and then aggregated by state and season. We found that upstairs/basement ratios of northeastern states are generally lower than those of Midwestern states, a pattern also found in 3508 pairs of simultaneous long-term radon measurements. Ratios in winter are higher than those in other seasons. Our results, in conjunction with behavior data, can improve the assessment of short-term residential exposure to radon and therefore facilitate future studies regarding the acute health effects of radon.
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| 4. |
- Metcalfe, Travis S., et al.
(författare)
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Asteroseismology and Spectropolarimetry of the Exoplanet Host Star Lambda Serpentis
- 2023
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Ingår i: Astronomical Journal. - : Institute of Physics (IOP). - 0004-6256 .- 1538-3881. ; 166:4
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Tidskriftsartikel (refereegranskat)abstract
- The bright star lambda Ser hosts a hot Neptune with a minimum mass of 13.6 M & OPLUS; and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface differential rotation very similar to the Sun. We aim to characterize the fundamental properties of this system and constrain the evolutionary pathway that led to its present configuration. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite, and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and estimate the wind braking torque. We conclude that the remaining uncertainty on the stellar age currently prevents an unambiguous interpretation of the properties of lambda Ser, and that the rate of angular momentum loss appears to be higher than for other stars with a similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.
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| 5. |
- Zhou, Yixiao, et al.
(författare)
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The relationship between photometric and spectroscopic oscillation amplitudes from 3D stellar atmosphere simulations
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 503:1, s. 13-27
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Tidskriftsartikel (refereegranskat)abstract
- We establish a quantitative relationship between photometric and spectroscopic detections of solar-like oscillations using ab initio, 3D, hydrodynamical numerical simulations of stellar atmospheres. We present a theoretical derivation as a proof of concept for our method. We perform realistic spectral line formation calculations to quantify the ratio between luminosity and radial velocity amplitude for two case studies: the Sun and the red giant ϵ Tau. Luminosity amplitudes are computed based on the bolometric flux predicted by 3D simulations with granulation background modelled the same way as asteroseismic observations. Radial velocity amplitudes are determined from the wavelength shift of synthesized spectral lines with methods closely resembling those used in Birmingham Solar Oscillations Network (BiSON) and Stellar Oscillations Network Group (SONG) observations. Consequently, the theoretical luminosity to radial velocity amplitude ratios are directly comparable with corresponding observations. For the Sun, we predict theoretical ratios of 21.0 and 23.7 ppm [m s−1]−1 from BiSON and SONG, respectively, in good agreement with observations 19.1 and 21.6 ppm [m s−1]−1. For ϵ Tau, we predict K2 and SONG ratios of 48.4 ppm [m s−1]−1, again in good agreement with observations 42.2 ppm [m s−1]−1, and much improved over the result from conventional empirical scaling relations that give 23.2 ppm [m s−1]−1. This study thus opens the path towards a quantitative understanding of solar-like oscillations, via detailed modelling of 3D stellar atmospheres.
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