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- Sallee, J. B., et al.
(author)
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Southern ocean carbon and heat impact on climate
- 2023
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In: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. - 1364-503X .- 1471-2962. ; 381:2249
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Journal article (peer-reviewed)abstract
- The Southern Ocean greatly contributes to the regulation of the global climate by controlling important heat and carbon exchanges between the atmosphere and the ocean. Rates of climate change on decadal timescales are therefore impacted by oceanic processes taking place in the Southern Ocean, yet too little is known about these processes. Limitations come both from the lack of observations in this extreme environment and its inherent sensitivity to intermittent processes at scales that are not well captured in current Earth system models. The Southern Ocean Carbon and Heat Impact on Climate programme was launched to address this knowledge gap, with the overall objective to understand and quantify variability of heat and carbon budgets in the Southern Ocean through an investigation of the key physical processes controlling exchanges between the atmosphere, ocean and sea ice using a combination of observational and modelling approaches. Here, we provide a brief overview of the programme, as well as a summary of some of the scientific progress achieved during its first half. Advances range from new evidence of the importance of specific processes in Southern Ocean ventilation rate (e.g. storm-induced turbulence, sea-ice meltwater fronts, wind-induced gyre circulation, dense shelf water formation and abyssal mixing) to refined descriptions of the physical changes currently ongoing in the Southern Ocean and of their link with global climate.This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.
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- Elimian, K, et al.
(author)
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Epidemiology, diagnostics and factors associated with mortality during a cholera epidemic in Nigeria, October 2020-October 2021: a retrospective analysis of national surveillance data
- 2022
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In: BMJ open. - : BMJ. - 2044-6055. ; 12:9, s. e063703-
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Journal article (peer-reviewed)abstract
- Nigeria reported an upsurge in cholera cases in October 2020, which then transitioned into a large, disseminated epidemic for most of 2021. This study aimed to describe the epidemiology, diagnostic performance of rapid diagnostic test (RDT) kits and the factors associated with mortality during the epidemic.DesignA retrospective analysis of national surveillance data.Setting33 of 37 states (including the Federal Capital Territory) in Nigeria.ParticipantsPersons who met cholera case definition (a person of any age with acute watery diarrhoea, with or without vomiting) between October 2020 and October 2021 within the Nigeria Centre for Disease Control surveillance data.Outcome measuresAttack rate (AR; per 100 000 persons), case fatality rate (CFR; %) and accuracy of RDT performance compared with culture using area under the receiver operating characteristic curve (AUROC). Additionally, individual factors associated with cholera deaths and hospitalisation were presented as adjusted OR with 95% CIs.ResultsOverall, 93 598 cholera cases and 3298 deaths (CFR: 3.5%) were reported across 33 of 37 states in Nigeria within the study period. The proportions of cholera cases were higher in men aged 5–14 years and women aged 25–44 years. The overall AR was 46.5 per 100 000 persons. The North-West region recorded the highest AR with 102 per 100 000. Older age, male gender, residency in the North-Central region and severe dehydration significantly increased the odds of cholera deaths. The cholera RDT had excellent diagnostic accuracy (AUROC=0.91; 95% CI 0.87 to 0.96).ConclusionsCholera remains a serious public health threat in Nigeria with a high mortality rate. Thus, we recommend making RDT kits more widely accessible for improved surveillance and prompt case management across the country.
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- Zayachuk, Y., et al.
(author)
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Impact of water ingress on deuterium release, oxidation, and dust generation in beryllium plasma-facing components
- 2023
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In: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 35
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Journal article (peer-reviewed)abstract
- Beryllium samples from the JET ITER-like wall limiter tiles with either co-deposits or surface cracks caused by melt damage, were immersed into boiling water for 4 h 15 min to simulate and assess the impact of coolant water ingress into a tokamak on the state of Be components. Microscopy of the water-treated surfaces and the lack of residue in the water revealed that no thermomechanical damage (cracking or exfoliation) occurred to the samples during the exposure. Ion beam analysis showed no measurable release of deuterium from the samples. Combined ion beam analysis and Raman spectroscopy indicated only some degree of surface oxidation, but no thick oxide films were formed.
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- Metcalfe, Travis S., et al.
(author)
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Asteroseismology and Spectropolarimetry of the Exoplanet Host Star Lambda Serpentis
- 2023
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In: Astronomical Journal. - : Institute of Physics (IOP). - 0004-6256 .- 1538-3881. ; 166:4
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Journal article (peer-reviewed)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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| 8. |
- Metcalfe, Travis S., et al.
(author)
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Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and tau Cet
- 2023
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In: Astrophysical Journal Letters. - : Institute of Physics (IOP). - 2041-8205 .- 2041-8213. ; 948:1
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Journal article (peer-reviewed)abstract
- During the first half of their main-sequence lifetimes, stars rapidly lose angular momentum to their magnetized winds, a process known as magnetic braking. Recent observations suggest a substantial decrease in the magnetic braking efficiency when stars reach a critical value of the Rossby number, the stellar rotation period normalized by the convective overturn timescale. Cooler stars have deeper convection zones with longer overturn times, reaching this critical Rossby number at slower rotation rates. The nature and timing of the transition to weakened magnetic braking have previously been constrained by several solar analogs and two slightly hotter stars. In this Letter, we derive the first direct constraints from stars cooler than the Sun. We present new spectropolarimetry of the old G8 dwarf tau Cet from the Large Binocular Telescope, and we reanalyze a published Zeeman Doppler image of the younger G8 star 61 UMa, yielding the large-scale magnetic field strengths and morphologies. We estimate mass-loss rates using archival X-ray observations and inferences from Ly alpha measurements, and we adopt other stellar properties from asteroseismology and spectral energy distribution fitting. The resulting calculations of the wind braking torque demonstrate that the rate of angular momentum loss drops by a factor of 300 between the ages of these two stars (1.4-9 Gyr), well above theoretical expectations. We summarize the available data to help constrain the value of the critical Rossby number, and we identify a new signature of the long-period detection edge in recent measurements from the Kepler mission.
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- Rubel, Marek, et al.
(author)
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Search for mobilised dust during operations with equipment for remote handling in JET with ITER-like wall
- 2020
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In: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; T171:1
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Journal article (peer-reviewed)abstract
- Accumulation of dust on the equipment for remotely handled (RH) operations was studied in JET with the ITER-like wall (JET-ILW) during the shutdown period following the third ILW campaign. The topic is connected to licensing procedures for ITER: the need to assess risks related to the external transfer of beryllium and radioactive matter with tritium and activation products. Ten adhesive carbon pads were placed in different locations on the robotic arm operated in-vessel for 672 h. Also air samplers were used during the RH operation and smear tests of the RH boom were performed to quantify specific contamination levels by beryllium and tritium. Dust morphology was determined by microscopy techniques. The areal density of dust varies at different sticker position on the boom. On some parts (e.g. 'wrists' of the robot) the density of particles exceeds 1000 per mm(2). Their morphology is very diverse but most collected objects originate from the construction material (aluminium) of the RH equipment itself. The accumulation of Be- and W-based particles is negligible. The study confirms earlier experimental evidence that Be-rich co-deposits (and also W coatings on CFC) adhere well to plasma-facing components and they are not easily mobilised.
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