| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Akiyama, Kazunori, et al.
(författare)
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First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5-11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of similar to 50 mu as, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*'s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.
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| 3. |
- Campbell, Charles, et al.
(författare)
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Bridging model and real catalysts: general discussion
- 2016
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Ingår i: Faraday Discussions. - 1359-6640 .- 1364-5498. ; 188, s. 565-589
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Charles Campbell opened the discussion of the paper by Hans-JoachimFreund: If you have a 3D gold particle and it spreads out to be a 2D particle whenyou adsorb CO2, it must gain energy stability. Did you estimate the energy changeof the overall process to do that?
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| 4. |
- Allan, Ian J., et al.
(författare)
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Evaluation of the Chemcatcher and DGT passive samplers for monitoring metals with highly fluctuating water concentrations
- 2007
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Ingår i: Journal of Environmental Monitoring. ; 9:7, s. 672-681
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Tidskriftsartikel (refereegranskat)abstract
- Passive sampling devices accumulate chems. continuously from water and can provide time weighted av. (TWA) concns. of pollutants over the exposure period. Hence, they offer a no. of advantages over other conventional monitoring techniques such as spot or grab sampling. The diffusive gradient in thin film (DGT) and the Chemcatcher passive samplers can be used to provide TWA concns. of labile metals, but the approaches to their calibration differ. DGT uses diffusion coeffs. of metals in the hydrogel layer, whereas Chemcatcher uses metal specific uptake rates, with both sets of values obtained under controlled lab. conditions with const. aq. metal concns. However, little is known of how such samplers respond to fluctuating concns. We evaluated the responsiveness of these two passive sampling devices to rapidly changing concns. of Cd, Cu, Ni, Pb and Zn in natural freshwater, over a relatively short deployment time. Maximum metal concns. in water were varied between 70 and 140 mg L-1. Expts. were carried out in a tank with a rotating carousel system and filled with Meuse River water, allowing a degree of control over exptl. conditions while using natural river water. Fluctuating concns. were obtained by stepwise addn. of std. solns. of the metals. The reliability and accuracy of the TWA concns. measured by the samplers were assessed by comparison with concns. of the metals in spot samples of water taken regularly over the deployment period. The spot samples of water were either unfiltered (total), filtered (0.45 mm) or ultrafiltered (5 kDa). Predictive speciation modeling using the visual MINTEQ program was also undertaken. There was reasonable agreement between the TWA concns. of Cd and Ni obtained with Chemcatcher and DGT and the total Cd and Ni concns. measured in repeated unfiltered spot samples. For elements (i.e. Cu, Pb, Zn) that assoc. to a significant degree with suspended solids, colloids or dissolved org. carbon, or form complexes with large org. ligands, optimum agreement was with the filtered or ultrafiltered fractions and with the predicted inorg. and inorg.-fulvic acid assocd. fractions. While Chemcatcher-based TWA concn. ranges for Cu and Zn were in best agreement with the total filtered fraction, there was lack of agreement for Pb. The combined use of DGT devices with open pore (OP) and restricted pore (RP) gels allowed the labile fraction of metal assocd. with large org. ligands or DOC to be differentiated and quantified, since this is available to DGT OP but unable to diffuse into the DGT RP. This evaluation of the two sampling devices clearly demonstrated their ability to react reliably to transient peaks in concn. of metal pollutants in water and indicated where future efforts are needed to improve calibration data. Such samplers may prove valuable in responding to the monitoring requirements of the European Union's Water Framework Directive. [on SciFinder (R)]
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| 5. |
- Allan, Ian J., et al.
(författare)
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Strategic monitoring for the European Water Framework Directive
- 2006
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Ingår i: TrAC - Trends in Analytical Chemistry. - : Elsevier BV. - 0165-9936. ; 25:7, s. 704-715
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Tidskriftsartikel (refereegranskat)abstract
- This article first reviews the principal monitoring requirements of the Water Framework Directive (WFD) of the European Union (EU) and assesses how contaminant monitoring may fit into a risk-assessment approach. In this context, we show the limited ability of conventional trace-contaminant-monitoring methods to fulfil all of the WFD requirements. We then clearly define and exemplify the roles and the functions of a new set of monitoring tools, using three case studies based on datasets that we obtained during a field trial in the River Meuse as part of the Screening methods for Water data InFormaTion (SWIFT-WFD) project in support of implementing the WFD.
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| 6. |
- Björklund-Persson, Lena, 1966, et al.
(författare)
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Performance of an in situ passive sampling system for metals in stormwater
- 2002
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Ingår i: Journal of Environmental Monitoring. - : Royal Society of Chemistry (RSC). - 1464-0333 .- 1464-0325. ; 4:2, s. 258-262
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Tidskriftsartikel (refereegranskat)abstract
- A passive sampler has been developed and is demonstrated in situ for urban runoff. The passive sampler is compared to conventional composite (time-dependent and flow-weighted) bottle sampling during and between storm events. The sampling was carried out at established stormwater stations; before and after a stormwater detention pond. In situ deployment of the passive sampler provides the metal concentrations, corresponding to the electrochemically available fraction of total metal, for time-dependent samples collected in parallel. The sampler provides improved accuracy compared to bottle sampling because contamination during sample transport and handling is minimised. Laboratory handling is reduced by direct analysis of the accumulated metals on the receiving membrane by laser ablation inductively coupled plasma mass spectrometry. Passive sampling also solves the problem of metal speciation change during transport to the laboratory, which is a potential problem for bottle samples. The low cost and convenience of the passive sampler and subsequent analysis should allow significantly more extensive spatial and temporal monitoring of metals in the aquatic environment than has previously been possible.
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| 7. |
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| 8. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 9. |
- Kim, Jae-Young, et al.
(författare)
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Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 640
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Tidskriftsartikel (refereegranskat)abstract
- 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique - global Very Long Baseline Interferometry (VLBI) at 1.3mm (230 GHz) - to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array, at an angular resolution of ∼20 μas (at a redshift of z = 0:536 this corresponds to ∼0:13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation.We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across diffierent imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI "core". This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet.We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of ∼15 c and ∼20 c (∼1:3 and ∼1:7 μas day-1, respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3mm core and the outer jet. The intrinsic brightness temperature of the jet components are ≤1010 K, a magnitude or more lower than typical values seen at ≥7mm wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.
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