Contaminated sediment from a marine harbour was maintained for 16 months in two flumes that continuously re-circulated the overlying water, sustaining a smooth flow at the sediment surface. The ...sediment was placed in one flume intact, while for the other it was pre-homogenised. The concentrations of trace metals in the porewaters were measured at a vertical resolution of 2 mm using the technique of diffusive equilibration in thin-films (DET) and microelectrodes were used to measure concentration profiles of oxygen and pH. Separate experiments showed good agreement between metals measured by DET and those measured in porewaters extracted by centrifugation and filtration. Local mobilisation of metals was measured in 2-dimensional arrays by deploying DGT (diffusive gradients in thin-films) probes. There were high concentrations of Fe in the porewaters, which limited the concentration of sulphide to less than 0.3 μM. With both DET and DGT measurements, there were sharply defined maxima of Cu and Cd within 2 mm of the sediment water interface, consistent with their release from organic material as it is oxidised. There was a Co maximum about 5–8 mm lower than the Cu and Cd maxima, apparently coincidental with Mn mobilisation. While there were clear Ni maxima, their location appeared to vary from being coincident with Co to a few mm above the Co maxima. The remobilisation of metals could not be explained by the pH gradients in the near-surface sediments. As sulphate reduction rates were appreciable, the apparent lack of metal mobilisation at depth was attributed to the formation of metal sulphides. The DGT measurements in the same probe were well replicated horizontally. This, the replication of the same features between flumes and the reasonable correspondence between DGT and DET, showed that the localised mobilisation of metals was associated with recent diagenetic processes, rather than the depositional history. There were substantial fluxes of Cu and Cd to the overlying water. Even though there were steep gradients of Fe, Mn, Ni and Co within 1 cm of the sediment–water interface, there was no clear evidence for any substantial metal fluxes across the interface. Adsorption of Mn to Fe oxides, rather than oxidation, may be responsible for its removal from solution at the same depth as Fe.
Specialization to a particular environment is one of the main factors used to explain species distributions. Antarctic fishes are often cited as a classic example to illustrate the specialization ...process and are regarded as the archetypal stenotherms. Here we show that the Antarctic fish Pagothenia borchgrevinki has retained the capacity to compensate for chronic temperature change. By displaying astounding plasticity in cardiovascular response and metabolic control, the fishes maintained locomotory performance at elevated temperatures. Our falsification of the specialization paradigm indicates that the effect of climate change on species distribution and extinction may be overestimated by current models of global warming.
A new sandwich sensor, consisting of an O2 planar optode overlain by a thin (90 µm) DGT layer is presented. This sensor can simultaneously resolve 2‐D O2 dynamics and trace metal fluxes in benthic ...substrates at a high spatial resolution. The DGT layer accumulates metals on a small particle size (0.2 µm) chelating resin and records the locally induced trace metal flux during the deployment, whereas the planar optode resolves the O2 dynamic in near real time at the same location in the sediment. Despite its ultrathin composition, the DGT layer has high carrying capacity for trace metals with no saturation problems during application to typical coastal‐ or contaminated sediments. Combined with laser ablation, accumulated metal fluxes could be resolved at a resolution of ~200 µm, whereas the O2 images had a resolution of ~100 µm. A 2‐D diffusion‐reaction model showed that the enhanced smearing and reduced response time of the O2 signal associated with the additional DGT layer were marginal. To test sensor performance at realistic conditions, it was applied to an artificial burrow system consisting of permeable dialysis tubing flushed with oxygenated seawater. The measurements demonstrated localized mobilization of Ni, Cu, and Pb close to the burrow wall, where O2 was elevated. The latter was also confirmed for Cu and Pb in natural sediments irrigated by the polychaete Hediste diversicolor. The sandwich sensor has great potential for investigating interrelations between O2 dynamics and metal mobilization in complex benthic systems such as burrows, rhizospheres, permeable sands, and microbial mats.
Vertical profiles of trace metals were measured at 1-mm intervals by deploying DGT probes in sediment cores collected from the deep Atlantic Ocean (Feni Drift) before and after the spring ...phytoplankton bloom. DGT (diffusive gradients in thin-films) accumulates metals on a chelating resin after their diffusive transport through a layer of hydrogel. The mean concentration of metal in the porewaters at the surface of the device during its deployment was derived from the measured mass of metal. Well-defined laboratory systems were used to establish the reproducibility and accuracy of the DGT technique for measuring metals at 1-mm intervals. The Fe and Mn profiles showed the expected redox sequence with depth, with additional fine-scale (2–5mm) features. The close correspondence between the Mn and Co profiles, on both coarse and fine scales, showed that their chemistry is closely coupled in sediments as well as water columns. Changes in the background concentrations of Cd, Cu, Ni and Zn with depth were well correlated with Mn and Co, but the four metals also displayed mm-scale maxima that were largely independent of Mn, Co or Fe. Two-dimensional measurements at a 100-μm resolution on a DGT probe, deployed in situ with an autonomous lander, showed that the maxima were most likely associated with near-spherical, highly localised sources. The results were consistent with release of Cd, Cu, Ni and Zn from organic and planktonic skeletal material. Where there was associated release of Mn and/or Fe, through their oxides acting as electron acceptors in the decomposition of the organic matter, trace metals could also be supplied by release from the oxides. The microniches responsible for high local concentrations of metals in the porewaters were hypothesised to be due to downward mixing of material by burrowing organisms, known to be prevalent in these sediments. Much of this material appeared to be present as faecal pellets of various origins, with sizes in the range of 50μm to 1cm.
A numerical model of the transport and dynamics of metal complexes in the resin and gel layers of a DGT (diffusive gradients in thin films) device was developed and used to investigate how the ...chelating resin and metal-ligand complexes in solution affect metal uptake. Decreasing the stability constant or concentration of the binding resin increases the competition for free metal ions by ligands in solution, lowering the rate of mass uptake. Such effects would be rarely observed for moderately or strongly binding resins (K> 10(12)), including Chelex, which out-compete labile ligands in solution. With weakly binding resins, strongly bound solution complexes can diffuse into the resin layer before a measurable amount of dissociation occurs, such that concentrations of bound metal at the rear and front surfaces of the resin layer are equal. With more strongly binding resins, metal mainly binds to the front surface of the resin. Only complexes with the largest binding constants penetrate the gel layer containing Chelex, buttheir lack of lability means thatthe DGT sensitivity to the complex is, in any case, very low. The slow diffusion of complexes, such as those of fulvic acids, which increases the time required to establish steady state, compromises the use of the simple DGT equation. Errors are negligible for 24 h deployments, when diffusive layer thicknesses are less than 1 mm, but 3 day deployments are required to ensure accuracy with 2.4 mm thick layers. The extent to which the commonly used equation, that accounts for the concentration and diffusion of metal-complex species, overestimates DGT uptake if the rate of dissociation is slow, was estimated.
The technique of diffusive gradients in thin films (DGT) with measurements by computer-imaging densitometry (CID) was used to study the in situ, two-dimensional distribution of sulfide-producing ...microniches in sediments from a eutrophic lake (Esthwaite Water, UK). The DGT-CID technique precipitates and immobilizes the net pore-water flux of dissolved sulfide as black Ag2S by reaction with a AgI binding gel. The mass of accumulated sulfide is then determined from a scanned grayscale image of this gel. DGT probes deployed in laboratory mesocosms of homogeneously mixed sediment, then analyzed at high spatial resolution (approximately 0.1 mm), showed that apparent niche areas (operationally defined by DGT-CID) were <1 mm2 for 30% of the niches. In eight DGT probes deployed in undisturbed sediment cores, the proportion of microniche-related sulfide flux was > or =1-8% of the total horizontal net pore-water flux of sulfide. This study suggests that microniches that introduce local redox gradients are common in sediments. As fluxes within these microenvironments can considerably exceed background values, consideration of the dynamics of the biogeochemical processes occurring at these sites is likely to be key to improving our understanding of early diagenesis. Measurement procedures and three-dimensional reaction-transport models should be designed with the aim of furthering understanding of the complexities associated with locally supplied particles of reactive organic matter.
Background
Prevention of secondary stroke following initial ictus is an important focus of after-stroke care. Blood pressure (BP) is a key risk factor, so usual care following stroke or transient ...ischaemic attack includes regular BP checks and monitoring of anti-hypertensive medication. This is traditionally carried out in primary care, but the evidence supporting self-monitoring and self-guided management of BP in the general population with hypertension is growing.
Objective
Our objective was to estimate the cost effectiveness of treatment as usual (TAU) versus (1) self-monitoring of BP (S-MON) and (2) self-monitoring and guided self-management of anti-hypertensive medication (S-MAN).
Methods
This was a within-trial economic evaluation of a randomised controlled trial estimating the incremental cost per 1 mmHg BP reduction and per quality-adjusted life-year (QALY) gained over a 6-month time horizon from the perspective of the UK National Health Service (NHS).
Results
Data were evaluable for 140 participants. Costs per patient were £473, £853 and £1035; mean reduction in systolic BP (SBP) was 3.6, 6.7 and 6.1 mmHg, and QALYs accrued were 0.427, 0.422 and 0.423 for TAU, S-MON and S-MAN, respectively. No statistically significant differences in incremental costs or outcomes were detected. On average, S-MAN was dominated or extended dominated. The incremental cost per 1 mmHg BP reduction from S-MON versus TAU was £137.
Conclusion
On average, S-MAN is an inefficient intervention. S-MON may be cost effective, depending on the willingness to pay for a 1 mmHg BP reduction, although it yielded fewer QALYs over the within-trial time horizon. Decision modelling is required to explore the longer-term costs and outcomes.
In situ measurements of Fe and Mn by dialysis and diffusive gradients in thin-films (DGT) in 5 lakes (pH 4.7-7.5, ionic strength 0.3-5 mmol l(-1)) and Cu and Zn in an acidic and circumneutral lake ...were compared to results from on site filtration. For the most acidic lake (pH 4.7) all measurements agreed, indicating an absence of colloids and negligible complexation by organic matter. There was little difference in the Mn concentrations measured by the three techniques for any lake, consistent with it being free from complexation. Zn measured by dialysis in circumneutral water was only slightly higher than DGT measurements, appropriate to only partial complexation. Substantial differences between dialysis and DGT for Cu were consistent with complexation by fulvic and humic substances, though not to the extent predicted by the speciation code WHAM. To achieve a good fit it was necessary to adjust the pK for Cu-fulvic binding from 0.8 to 1.3 and to assume that fulvic substances dominated. The presence of low molecular weight strong binding ligands would also be consistent with the data. Differences between the three measurement methods were greatest for Fe, attributable to the presence of large oxyhydroxide colloids, organic complexation and low molecular weight, reactive hydrolysis products. Fe and Mn concentrations measured by DGT on samples returned to the laboratory were much lower than in situ concentrations, illustrating the need for in situ measurements. While use of two in situ techniques provided useful information on the speciation of these natural waters, further refinements are required for unambiguous characterization of the solution. The use of DGT with a more restricted gel that excludes complexes with humic substances should provide complementary information to in situ dialysis.
STag: Supernova Tagging and Classification Davison, William; Parkinson, David; Tucker, Brad E.
The Astrophysical journal,
02/2022, Letnik:
925, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
Supernovae classes have been defined phenomenologically, based on spectral features and time series data, since the specific details of the physics of the different explosions remain ...unrevealed. However, the number of these classes is increasing as objects with new features are observed, and the next generation of large surveys will only bring more variety to our attention. We apply the machine learning technique of multi-label classification to the spectra of supernovae. By measuring the probabilities of specific features or “tags” in the supernova spectra, we can compress the information from a specific object down to that suitable for a human or database scan, without the need to directly assign to a reductive “class”. We use logistic regression to assign tag probabilities, and then a feed-forward neural network to filter the objects into the standard set of classes, based solely on the tag probabilities. We present
STag
, a software package that can compute these tag probabilities and make spectral classifications.
PDF
