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851.
Allen S. Krieger 《Solar physics》1978,56(1):107-120
The sizes and shapes of X-ray emitting loops brightened by flares and other coronal transients have been derived from the Skylab S-054 photographs. This information has been combined with estimates of temperature and emission measure derived from the photographs and from Solrad data to compute brightness decay times attributable to various coronal energy loss mechanisms. The computed decay times are compared to those actually observed. Examples are presented of the brightness decay of soft X-ray flare kernels, post-flare loops, and the coronal X-ray enhancement asssociated with an H filament disappearance.The computed decay time due to conductive losses is always found to be much more rapid than that due to radiative losses in the corona. However, the observed soft X-ray brightness decay times are always much longer than those computed from conductive cooling.The role of geometrical inhibition of conduction as discussed by Antiochos and Sturrock (1976a) is examined for these events. It is shown that this mechanism might be adequate to account for the observed results in two of the five cases examined, but it is inadequate in the other three. The possible breakdown of classical collisional thermal conductivity (Forslund, 1970) is examined and it is shown that this mechanism is not applicable to the cases presented here. Confirmation of the existence of the very high conductive fluxes predicted by the coronal flare conductive cooling models is sought from EUV and H observations. No evidence is found which unequivocally demonstrates the presence, at lower levels in the atmosphere, of very high conductive fluxes. The soft X-ray results are consistent with the continuation of evaporation driven by thermal conduction (Antiochos and Sturrock, 1976b) late into the decay phase of the event. In this case, no source of continued magnetic energy dissipation after the initial stages of the flare is required to explain the lifetime of the X-ray emitting loops. 相似文献
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855.
Iskender Sahin Assistant Professor Allen H. Magnuson Asssciate Professor 《Ocean Engineering》1984,11(5):451-461
A modified source-and-dipole type singularity panel method is proposed to calculate the flow properties for an oscillating arbitrary body in the presence of a free surface. The technique is based on Green's identity whereby the boundary value problem is expressed as a boundary integral equation which is solved numerically. The free-space Green function is used in the integral equation. To demonstrate the feasibility of the method, the problem of a pulsating submerged line source under a free surface is treated and results are compared with the exact solution.An excellent agreement with the theory is obtained for panel density of about ten panels per wavelength and paneled water surface length of two wavelengths with very low computing times, indicating the feasibility of the method for unsteady water wave problems. 相似文献
856.
Christel Prudhomme Andy Young Glenn Watts Tracey Haxton Sue Crooks Jennifer Williamson Helen Davies Simon Dadson Stuart Allen 《水文研究》2012,26(7):1115-1118
As climate change may modify the hydrological cycle significantly, understanding the impact on river flow is important because it affects long‐term water resources planning. Here, we describe a high‐resolution British assessment of changes in river flows in the 2050s under 11 different realisations of HadRM3. In winter, river flows may either increase or decrease, with a wide range of possible decreases in summer flow. These results should encourage adaptation that copes with a broad range of future hydrological conditions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
857.
In a recent Letter, Litvinenko, Forbes, and Priest (1996) claimed that the rate of the very fast flux-pile up reconnection is severely limited by the effects of plasma pressure. They considered however only two-dimensional, zero-vorticity flows. Here we show that this limitation is a feature of these restrictive assumptions and can be removed by relaxing either of them. 相似文献
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859.
Sonia Scarselli Guy D. H. Simpson Philip A. Allen Giorgio Minelli Lorenzo Gaudenzi 《地学学报》2007,19(1):74-81
The Marche Apennines (Italy) offer an excellent opportunity to constrain the temporal and spatial relationships between drainage network formation and tectonic activity. Using a combination of field data, seismic lines and boreholes we show that the main deformation phase took place during the Messinian when the area, affected by the Messinian sea level drop, emerged and evolved from marine to continental conditions. The results highlight that during the Messinian emersion a drainage network developed contemporaneously with an increase in tectonic activity that could be related to sea level fall and river erosion. The present‐day river system, which is dominated by transverse rivers that cut straight across the tectonic grain, is located in older Messinian palaeovalleys, even though the region was subsequently covered by water until the late Pliocene–early Pleistocene. 相似文献