| 31. |
- Lee, Ben H, et al.
(författare)
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Highly functionalized organic nitrates in the southeast United States: Contribution to secondary organic aerosol and reactive nitrogen budgets.
- 2016
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 1091-6490. ; 113:6, s. 1516-21
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Tidskriftsartikel (refereegranskat)abstract
- Speciated particle-phase organic nitrates (pONs) were quantified using online chemical ionization MS during June and July of 2013 in rural Alabama as part of the Southern Oxidant and Aerosol Study. A large fraction of pONs is highly functionalized, possessing between six and eight oxygen atoms within each carbon number group, and is not the common first generation alkyl nitrates previously reported. Using calibrations for isoprene hydroxynitrates and the measured molecular compositions, we estimate that pONs account for 3% and 8% of total submicrometer organic aerosol mass, on average, during the day and night, respectively. Each of the isoprene- and monoterpenes-derived groups exhibited a strong diel trend consistent with the emission patterns of likely biogenic hydrocarbon precursors. An observationally constrained diel box model can replicate the observed pON assuming that pONs (i) are produced in the gas phase and rapidly establish gas-particle equilibrium and (ii) have a short particle-phase lifetime (∼2-4 h). Such dynamic behavior has significant implications for the production and phase partitioning of pONs, organic aerosol mass, and reactive nitrogen speciation in a forested environment.
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| 32. |
- Mahajan, Anubha, et al.
(författare)
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Trans-ethnic Fine Mapping Highlights Kidney-Function Genes Linked to Salt Sensitivity
- 2016
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Ingår i: American Journal of Human Genetics. - : Elsevier BV. - 0002-9297 .- 1537-6605. ; 99:3, s. 636-646
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Tidskriftsartikel (refereegranskat)abstract
- We analyzed genome-wide association studies (GWASs), including data from 71,638 individuals from four ancestries, for estimated glomerular filtration rate (eGFR), a measure of kidney function used to define chronic kidney disease (CKD). We identified 20 loci attaining genome-wide-significant evidence of association (p < 5 × 10(-8)) with kidney function and highlighted that allelic effects on eGFR at lead SNPs are homogeneous across ancestries. We leveraged differences in the pattern of linkage disequilibrium between diverse populations to fine-map the 20 loci through construction of "credible sets" of variants driving eGFR association signals. Credible variants at the 20 eGFR loci were enriched for DNase I hypersensitivity sites (DHSs) in human kidney cells. DHS credible variants were expression quantitative trait loci for NFATC1 and RGS14 (at the SLC34A1 locus) in multiple tissues. Loss-of-function mutations in ancestral orthologs of both genes in Drosophila melanogaster were associated with altered sensitivity to salt stress. Renal mRNA expression of Nfatc1 and Rgs14 in a salt-sensitive mouse model was also reduced after exposure to a high-salt diet or induced CKD. Our study (1) demonstrates the utility of trans-ethnic fine mapping through integration of GWASs involving diverse populations with genomic annotation from relevant tissues to define molecular mechanisms by which association signals exert their effect and (2) suggests that salt sensitivity might be an important marker for biological processes that affect kidney function and CKD in humans.
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| 33. |
- Mahiey, S, et al.
(författare)
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A Broadband Frequency Tripler for SIS Receivers
- 1998
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Ingår i: Ninth International Symposium on Space Terahertz Technology. ; , s. 481-491
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Konferensbidrag (refereegranskat)abstract
- Considerable success has recently been gained in the design and production of high powered frequency triplers incorporating Schottky varactor diodes. The design approach that was used for this goal has now been turned to the design of fixed tuned, broadband frequency triplers specifically intented for use in SIS receivers.The tripler reported here makes the use of a Heterostructure Barrier Varactor or HBV. A waveguide circuit has been designed that provides more than 50µW of output power for an input power of 10mW over a frequency range of 250 - 300GHz completely fixed tuned and without the need for bias.Further modification of the waveguide circuit should extend the useful fixed tuned bandwidth to greater than 100GHz centered at 300GHz.
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| 34. |
- McCarrick, Heather, et al.
(författare)
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The Simons Observatory Microwave SQUID Multiplexing Detector Module Design
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 922:1
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Tidskriftsartikel (refereegranskat)abstract
- Advances in cosmic microwave background (CMB) science depend on increasing the number of sensitive detectors observing the sky. New instruments deploy large arrays of superconducting transition-edge sensor (TES) bolometers tiled densely into ever larger focal planes. High multiplexing factors reduce the thermal loading on the cryogenic receivers and simplify their design. We present the design of focal-plane modules with an order of magnitude higher multiplexing factor than has previously been achieved with TES bolometers. We focus on the novel cold readout component, which employs microwave SQUID multiplexing (μmux). Simons Observatory will use 49 modules containing 70,000 bolometers to make exquisitely sensitive measurements of the CMB. We validate the focal-plane module design, presenting measurements of the readout component with and without a prototype detector array of 1728 polarization-sensitive bolometers coupled to feedhorns. The readout component achieves a 95% yield and a 910 multiplexing factor. The median white noise of each readout channel is 65 pA √Hz . This impacts the projected SO mapping speed by <8%, which is less than is assumed in the sensitivity projections. The results validate the full functionality of the module. We discuss the measured performance in the context of SO science requirements, which are exceeded.
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| 35. |
- Militello, Fulvio, et al.
(författare)
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Characterisation of the L-mode scrape off layer in MAST: decay lengths
- 2016
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 56:1, s. 016006-
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a detailed characterisation of the MAST Scrape Off Layer in L-mode. Scans in line averaged density, plasma current and toroidal magnetic field were performed. A comprehensive and integrated study of the SOL was allowed by the use of a wide range of diagnostics. In agreement with previous results, an increase of the line averaged density induced a broadening of the midplane density profile. This increase was not correlated with divertor detachment, as confirmed by the systematic increase of the target ion flux and decrease of the ${{D}_{\gamma}}/{{D}_{\alpha}}$ emission. Also, no clear correlation is found with the density of the neutral particles at the wall. At comparable density levels, discharges with higher current did not show broadening. Outer target ion saturation current and heat flux decay lengths were measured and compared with midplane data. For the saturation current, the upstream projections of the target values, based on diffusive models, did not match the midplane measurements, neither in amplitude nor in trend, while agreement was found for the heat fluxes, suggesting a different perpendicular transport mechanism for the two channels. Furthermore, the value of the target heat flux decay length was quite insensitive to changes in the thermodynamic conditions, in agreement with recent scaling laws. In all the cases studied, sawtooth oscillations were present but they simply rescaled self-similarly the target profiles. The separatrix conditions changed significantly during a sawtooth cycle, but the target heat flux decay length and divertor spreading factor remained nearly constant, indicating that these quantities are rather insensitive to the upstream thermodynamic state of the SOL.
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| 36. |
- Mylrea-Foley, Bronacha, et al.
(författare)
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Perinatal and 2-year neurodevelopmental outcome in late preterm fetal compromise : the TRUFFLE 2 randomised trial protocol
- 2022
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Ingår i: BMJ Open. - : BMJ Publishing Group Ltd. - 2044-6055. ; 12:4
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Following the detection of fetal growth restriction, there is no consensus about the criteria that should trigger delivery in the late preterm period. The consequences of inappropriate early or late delivery are potentially important yet practice varies widely around the world, with abnormal findings from fetal heart rate monitoring invariably leading to delivery. Indices derived from fetal cerebral Doppler examination may guide such decisions although there are few studies in this area. We propose a randomised, controlled trial to establish the optimum method of timing delivery between 32 weeks and 36 weeks 6 days of gestation. We hypothesise that delivery on evidence of cerebral blood flow redistribution reduces a composite of perinatal poor outcome, death and short-term hypoxia-related morbidity, with no worsening of neurodevelopmental outcome at 2 years.Methods and analysis: Women with non-anomalous singleton pregnancies 32+0 to 36+6 weeks of gestation in whom the estimated fetal weight or abdominal circumference is <10th percentile or has decreased by 50 percentiles since 18-32 weeks will be included for observational data collection. Participants will be randomised if cerebral blood flow redistribution is identified, based on umbilical to middle cerebral artery pulsatility index ratio values. Computerised cardiotocography (cCTG) must show normal fetal heart rate short term variation (>= 4.5 msec) and absence of decelerations at randomisation. Randomisation will be 1:1 to immediate delivery or delayed delivery (based on cCTG abnormalities or other worsening fetal condition). The primary outcome is poor condition at birth and/or fetal or neonatal death and/or major neonatal morbidity, the secondary non-inferiority outcome is 2-year infant general health and neurodevelopmental outcome based on the Parent Report of Children's Abilities-Revised questionnaire.Ethics and dissemination: The Study Coordination Centre has obtained approval from London-Riverside Research Ethics Committee (REC) and Health Regulatory Authority (HRA). Publication will be in line with NIHR Open Access policy.
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| 37. |
- Pemberton, Hugh G., et al.
(författare)
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Automated quantitative MRI volumetry reports support diagnostic interpretation in dementia : a multi-rater, clinical accuracy study
- 2021
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Ingår i: European Radiology. - : Springer. - 0938-7994 .- 1432-1084. ; 31:7, s. 5312-5323
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Tidskriftsartikel (refereegranskat)abstract
- Objectives We examined whether providing a quantitative report (QReport) of regional brain volumes improves radiologists' accuracy and confidence in detecting volume loss, and in differentiating Alzheimer's disease (AD) and frontotemporal dementia (FTD), compared with visual assessment alone. Methods Our forced-choice multi-rater clinical accuracy study used MRI from 16 AD patients, 14 FTD patients, and 15 healthy controls; age range 52-81. Our QReport was presented to raters with regional grey matter volumes plotted as percentiles against data from a normative population (n = 461). Nine raters with varying radiological experience (3 each: consultants, registrars, 'non-clinical image analysts') assessed each case twice (with and without the QReport). Raters were blinded to clinical and demographic information; they classified scans as 'normal' or 'abnormal' and if 'abnormal' as 'AD' or 'FTD'. Results The QReport improved sensitivity for detecting volume loss and AD across all raters combined (p = 0.015* and p = 0.002*, respectively). Only the consultant group's accuracy increased significantly when using the QReport (p = 0.02*). Overall, raters' agreement (Cohen's kappa) with the 'gold standard' was not significantly affected by the QReport; only the consultant group improved significantly (kappa(s) 0.41 -> 0.55, p = 0.04*). Cronbach's alpha for interrater agreement improved from 0.886 to 0.925, corresponding to an improvement from 'good' to 'excellent'. Conclusion Our QReport referencing single-subject results to normative data alongside visual assessment improved sensitivity, accuracy, and interrater agreement for detecting volume loss. The QReport was most effective in the consultants, suggesting that experience is needed to fully benefit from the additional information provided by quantitative analyses.
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| 38. |
- Prytherch, John, et al.
(författare)
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Air-sea CO2 and CH4 gas transfer velocity in Arctic sea-ice regions from eddy covariance flux measurements onboard Icebreaker Oden
- 2017
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Ingår i: Geophysical Research Abstracts. - 1029-7006 .- 1607-7962. ; 19
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic Ocean is an important sink for atmospheric CO2, and there is ongoing debate on whether seafloor seeps in the Arctic are a large source of CH4 to the atmosphere. The impact of warming waters, decreasing sea-ice extent and expanding marginal ice zones on Arctic air-sea gas exchange depends on the rate of gas transfer in the presence of sea ice. Sea ice acts as a near-impermeable lid to air-sea gas exchange, but is also hypothesised to enhance gas transfer rates through physical processes such as increased surface-ocean turbulence from ice-water shear and ice-edge form drag. The dependence of the gas transfer rate on sea-ice concentration remains uncertain due to a lack of in situ measurements. Here we present the first direct estimates of gas transfer rate in a wide range of Arctic sea-ice conditions. The estimates were derived from eddy covariance CO2 and CH4 fluxes, measured from the Swedish Icebreaker Oden during two expeditions: the 3-month duration Arctic Clouds in Summer Experiment (ACSE) in 2014, a component of the Swedish-Russian-US Arctic Ocean Investigation on Climate-Cryosphere-Carbon Interactions (SWERUS-C3) in the eastern Arctic Ocean shelf region; and the Arctic Ocean 2016 expedition to the high latitude Arctic Ocean. Initial CO2 results from ACSE showed that the gas transfer rate has a near-linear dependence on sea-ice concentration, and that some previous indirect measurements and modelling estimates overestimate gas transfer rates in sea-ice regions. This supports a linear sea-ice scaling approach for assessments of polar ocean carbon fluxes. Air-sea gas transfer model assumptions (e.g. Schmidt number dependence) will be examined using simultaneous CO2 and CH4 measurements, and observations in different ice conditions (e.g. summer melt, autumn freeze up, central Arctic and marginal ice zones) will be compared.
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| 39. |
- Prytherch, John, et al.
(författare)
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Central Arctic Ocean surface-atmosphere exchange of CO2 and CH4 constrained by direct measurements
- 2024
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Ingår i: Biogeosciences. - : Copernicus Publications. - 1726-4170 .- 1726-4189. ; 21:2, s. 671-688
-
Tidskriftsartikel (refereegranskat)abstract
- The central Arctic Ocean (CAO) plays an important role in the global carbon cycle, but the current and future exchange of the climate-forcing trace gases methane (CH4) and carbon dioxide (CO2) between the CAO and the atmosphere is highly uncertain. In particular, there are very few observations of near-surface gas concentrations or direct air-sea CO2 flux estimates and no previously reported direct air-sea CH4 flux estimates from the CAO. Furthermore, the effect of sea ice on the exchange is not well understood. We present direct measurements of the air-sea flux of CH4 and CO2, as well as air-snow fluxes of CO2 in the summertime CAO north of 82.5 N from the Synoptic Arctic Survey (SAS) expedition carried out on the Swedish icebreaker Oden in 2021. Measurements of air-sea CH4 and CO2 flux were made using floating chambers deployed in leads accessed from sea ice and from the side of Oden, and air-snow fluxes were determined from chambers deployed on sea ice. Gas transfer velocities determined from fluxes and surface-water-dissolved gas concentrations exhibited a weaker wind speed dependence than existing parameterisations, with a median sea-ice lead gas transfer rate of 2.5cmh-1 applicable over the observed 10m wind speed range (1-11ms-1). The average observed air-sea CO2 flux was -7.6mmolm-2d-1, and the average air-snow CO2 flux was -1.1mmolm-2d-1. Extrapolating these fluxes and the corresponding sea-ice concentrations gives an August and September flux for the CAO of -1.75mmolm-2d-1, within the range of previous indirect estimates. The average observed air-sea CH4 flux of 3.5μmolm-2d-1, accounting for sea-ice concentration, equates to an August and September CAO flux of 0.35μmolm-2d-1, lower than previous estimates and implying that the CAO is a very small (‰ 1%) contributor to the Arctic flux of CH4 to the atmosphere.
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| 40. |
- Prytherch, John, et al.
(författare)
-
Central Arctic Ocean surface-atmosphere exchange of CO2 and CH4 constrained by direct measurements
- 2024
-
Ingår i: Biogeosciences. - : Copernicus Publications. - 1726-4170 .- 1726-4189. ; 21, s. 671-688
-
Tidskriftsartikel (refereegranskat)abstract
- The central Arctic Ocean (CAO) plays an important role in the global carbon cycle, but the current and future exchange of the climate-forcing trace gases methane (CH4) and carbon dioxide (CO2) between the CAO and the atmosphere is highly uncertain. In particular, there are very few observations of near-surface gas concentrations or direct air-sea CO2 flux estimates and no previously reported direct air-sea CH4 flux estimates from the CAO. Furthermore, the effect of sea ice on the exchange is not well understood. We present direct measurements of the air-sea flux of CH4 and CO2, as well as air-snow fluxes of CO2 in the summertime CAO north of 82.5 N from the Synoptic Arctic Survey (SAS) expedition carried out on the Swedish icebreaker Oden in 2021. Measurements of air-sea CH4 and CO2 flux were made using floating chambers deployed in leads accessed from sea ice and from the side of Oden, and air-snow fluxes were determined from chambers deployed on sea ice. Gas transfer velocities determined from fluxes and surface-water-dissolved gas concentrations exhibited a weaker wind speed dependence than existing parameterisations, with a median sea-ice lead gas transfer rate of 2.5 cm h-1 applicable over the observed 10m wind speed range (1-11 m s-1). The average observed air-sea CO2 flux was -7.6 mmol m-2 d-1, and the average air-snow CO2 flux was -1.1 mmol m-2 d-1. Extrapolating these fluxes and the corresponding sea-ice concentrations gives an August and September flux for the CAO of -1.75 mmol m-2 d-1, within the range of previous indirect estimates. The average observed air-sea CH4 flux of 3.5 μmol m-2 d-1, accounting for sea-ice concentration, equates to an August and September CAO flux of 0.35 μmol m-2 d-1, lower than previous estimates and implying that the CAO is a very small (<< 1%) contributor to the Arctic flux of CH4 to the atmosphere.
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