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- Catalán, Núria, 1985-, et al.
(författare)
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Behind the Scenes : mechanisms Regulating Climatic Patterns of Dissolved Organic Carbon Uptake in Headwater Streams
- 2018
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Ingår i: Global Biogeochemical Cycles. - : American Geophysical Union (AGU). - 0886-6236 .- 1944-9224. ; 32:10, s. 1528-1541
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Tidskriftsartikel (refereegranskat)abstract
- Large variability in dissolved organic carbon (DOC) uptake rates has been reported for headwater streams, but the causes of this variability are still not well understood. Here we assessed acetate uptake rates across 11 European streams comprising different ecoregions by using whole-reach pulse acetate additions. We evaluated the main climatic and biogeochemical drivers of acetate uptake during two seasonal periods. Our results show a minor influence of sampling periods but a strong effect of climate and dissolved organic matter (DOM) composition on acetate uptake. In particular, mean annual precipitation explained half of the variability of the acetate uptake velocities (Vf(Acetate)) across streams. Temperate streams presented the lowest Vf(Acetate), together with humic-like DOM and the highest stream respiration rates. In contrast, higher Vf(Acetate) were found in semiarid streams, with protein-like DOM, indicating a dominance of reactive, labile compounds. This, together with lower stream respiration rates and molar ratios of DOC to nitrate, suggests a strong C limitation in semiarid streams, likely due to reduced inputs from the catchment. Overall, this study highlights the interplay of climate and DOM composition and its relevance to understand the biogeochemical mechanisms controlling DOC uptake in streams. Plain Language Summary Headwater streams receive and degrade organic carbon and nutrients from the surrounding catchments. That degradation can be assessed by measuring the uptake of simple compounds of carbon or nitrogen such as acetate or nitrate. Here we determine the variability in acetate and nitrate uptake rates across headwater streams and elucidate the mechanisms behind that variability. The balance between nutrients, the composition of the organic materials present in the streams, and the climatic background is at interplay.
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| 2. |
- Wang, L., et al.
(författare)
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On the use of a metasurface prism in gap-waveguide technology to reduce the dispersion of leaky-wave antennas
- 2018
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Ingår i: IET Conference Publications. - : Institution of Engineering and Technology.
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Konferensbidrag (refereegranskat)abstract
- Leaky-wave antennas (LWAs) feature the advantages of high directivity, wide impedance bandwidth, and their ability to scan with frequency. However, the dispersive beam-scanning makes the LWAs very difficult to be utilized in systems that require high-speed data transfer, wide band and high directive antennas. This paper proposes a simple but effective method to reduce the dispersion of LWAs by loading with a metasurface prism realized in gap-waveguide technology. Naturally combining the two technologies, a leaky-wave gap waveguide antenna and a dispersive prism, a low-dispersive gap-waveguide leaky-wave antenna is achieved, with a specific radiation direction that in this example is =4l°. The main radiation direction varies only ±0.5° from 11.5 to 13.0 GHz, with side-lobe levels lower than -13 dB. A 20% half-power gain-drop frequency bandwidth has been obtained. The realized gain varies from 16.4 to 16.8 dBi with a narrow half-power beamwidth of 5°. The full-wave simulations in HFSS agree well with the theoretical calculations.
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