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101.
The backscatter process for low energy electrons in the upper atmosphere is studied, and it is shown how variations in the pitch-angle and energy distributions of these particles may affect the backscatter ratio and also the electron component of the upward Birkeland current. “Softening” of the electron energy spectrum combined with a field-alignment of the electron fluxes may enhance the current carried by the greater than 200 eV energy electrons significantly. 相似文献
102.
Nils Ekeroth Magnus Lindstr?m Sven Blomqvist Per O. J. Hall 《Aquatic Geochemistry》2012,18(6):499-513
In recent decades, eutrophication has increased the extent of hypoxic and anoxic conditions in many coastal marine environments. In such conditions, the nutrient flux across the sediment?Cwater interface is a key process controlling the biogeochemical dynamics, and thereby the level and character of biological production. In some areas, management attempts to drive the ecosystem towards phosphorus (P) limitation, which calls for reliable knowledge on the mechanisms controlling P-cycling. We report a well-controlled laboratory experiment on benthic fluxes of P, when shifting from a state of hypoxic and azoic sediments to oxic and zoic bottom conditions. Adding any of three types of macrobenthic fauna (mysid shrimp, pontoporeid amphipod and tellinid clam) to oxygenated aquarium sections resulted in benthic P fluxes that differed consistently from the azoic control sections. All species caused liberation of dissolved organically bound P (DOP) from the sediment, in contrast to the azoic systems. The shrimp and the amphipod also resuspended the sediment, which resulted in a release of P bound to particles (>0.45???m). Dissolved inorganic phosphate (DIP) was released during hypoxic conditions, but was taken up after oxygenation, irrespective of the presence or absence of bottom fauna. In the presence of fauna, the uptake of DIP roughly equalled the release of DOP, suggesting that the benthic efflux of DOP following oxygenation and bottom fauna (re)colonisation might be considerable. This is an hitherto overlooked animal-controlled nutrient flux, which is missing from coastal marine P budgets. 相似文献
103.
An interpretation of a series of precise relationships (Barricelli, 1972a) between planetary perihelion and aphelion distances, leading to the definition of preferential perihelion and aphelion distances, designated as meeting distances is outlined. The interpretation is based on Alfvén's (1969) jet stream theory and the hypothesis of harmonic resonance between intersecting jet streams. 相似文献
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An experimental study of rip channel flow 总被引:2,自引:0,他引:2
Nils Drnen Harshinie Karunarathna Jrgen Fredse B. Mutlu Sumer Rolf Deigaard 《Coastal Engineering》2002,45(3-4)
A laboratory study of the flow over a bar with a single rip channel has been performed. First, the well-known pattern of a bar circulation cell with a strong offshore-directed current out through the rip channel and a weaker onshore-directed return flow over the bar is documented. Then measurements of the three-dimensional structure of the flow in the area where the rip channel, the bar and the trough meet and well inside the rip channel are presented. These measurements reveal that 3D effects play an important role, and that a depth-integrated viewpoint may not always be sufficient for predicting the flow in the near bed region. Particle-tracking experiments illustrate the near bed flow pattern over the entire area. These demonstrate how the overall trajectory pattern changes as a function of the distance of wave breaking from the bar crest: For some conditions, the rip current is fed from the trough and for other conditions it is fed directly from the bar. Both the 3D measurements and the trajectory tests show the existence of a weaker onshore-directed near-bed drift in the area where the rip current ceases. Finally, in a series of sensitivity tests, measurements of the rip current intensity for different wave climate and water level conditions reveal a strong correlation between the rip current intensity and the wave height (both normalized). 相似文献
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Nils Edelman 《International Journal of Earth Sciences》1967,56(1):362-363
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