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71.
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73.
Propagation of solar flare-associated interplanetary shock waves in the heliospheric meridional plane 总被引:4,自引:0,他引:4
We have analyzed 149 flare-associated shock wave events based on interplanetary scintillation (IPS) observational data. All of the flare-associated shock waves tend to propagate toward the low latitude region near the solar equator for flares that are located in both the solar northern and southern hemispheres. Also, the fastest propagation directions tend toward the heliospheric current sheet near 1 AU. We suggest that this tendency is caused by the dynamic action of near-Sun magnetic forces on the ejected coronal plasma that traverses the helmet-like magnetic topologies near the Sun outward to the classical topology that is essentially parallel to the heliospheric current sheet. 相似文献
74.
A grid of seismic reflection lines has been used to image basal topography and infer basal conditions and flow processes beneath ~140 km2 of Rutford Ice Stream, West Antarctica. The subglacial topography in this region consists of two troughs flanking a central high and the bed is composed of water-saturated sediments. The two troughs are filled with deforming sediment, whereas the bed in the central region appears to undergo a transition from largely deforming conditions upstream to basal sliding downstream. The deforming bed is very flat along flow, but undulates across flow. Sliding areas show rougher bed topography. Cross-stream bed topography is characterised by streamlined mounds of deforming sediment aligned in the ice flow direction. These bedforms occur superimposed on the bed in regions of both basal sliding and sediment deformation. In places, they form finger-like mounds of material, which extend into the sliding region further downstream. Mean bedform height is 22 m, mean width is 267 m, and many of them extend for at least 1–2 km along flow. We interpret most of these bedforms as drumlins and one as a mega-scale glacial lineation. The juxtaposition of different basal conditions is consistent with models proposed from terrestrial studies in which the glacier bed is a mosaic of stable and deforming bed areas, variable both spatially and temporally. Any theory of subglacial sediment rheology must also be able to account for our conclusion that, at any given time, pervasive deformation extends at least a few metres into the bed and can persist over a considerable area (many km2). Bedform geometry and basal conditions concur with interpretations of former ice streams, with evidence for increasing elongation ratio with distance downstream. However, those studies also identified bedrock cropping out at the ice-bed interface, for which there is no evidence on Rutford Ice Stream. 相似文献
75.
Evidence for threshold gradients is reviewed. The consolidation problem, with threshold gradient, is properly formulated and solved numerically. An approximate analytical solution is also developed. The influence of a threshold gradient on the time rate of settlement is examined, and it is shown that by modifying the definition of the degree of consolidation a good approximation to the threshold gradient problem can be obtained directly from the Terzaghi solution. It is also shown that threshold gradients will have no influence on odometer testing and their effect is, therefore, to reduce the primary compression below that predicted from standard tests. 相似文献
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77.
Christopher Packham Keith L. Thompson Almudena Zurita Johan H. Knapen Ian Smail Robert Greimel Daniel F. M. Folha Chris Benn rew Humphrey Rene Rutten David Ciardi Matthieu Bec Richard Bingham Simon Craig Kevin Dee Derek Ives Paul Jolley Peter Moore Marti Pi i Puig Simon Rees Gordon Talbot Sue Worswick 《Monthly notices of the Royal Astronomical Society》2003,345(2):395-405
78.
Using Cassini images, we examine the faint material along the orbits of Methone, Anthe and Pallene, three small moons that reside between the orbits of Mimas and Enceladus. A continuous ring of material covers the orbit of Pallene; it is visible at extremely high phase angles and appears to be localized vertically to within ±25 km of Pallene's inclined orbit. By contrast, the material associated with Anthe and Methone appears to lie in longitudinally confined arcs. The Methone arc extends over ∼10° in longitude around the satellite's position, while the Anthe arc reaches ∼20° in length. The extents of these arcs are consistent with their confinement by nearby corotation eccentricity resonances with Mimas. Anthe has even been observed to shift in longitude relative to its arc in the expected manner given the predicted librations of the moon. 相似文献
79.
We have found sorted stone circles and polygons near the equator of Mars, using new 25 cm/pixel NASA HiRISE (High Resolution Imaging Science Experiment) images. The sorted circles occur in geologically recent catastrophic flood deposits in the equatorial Elysium Planitia region, and are diagnostic of periglacial processes: sorted polygons do not form from volcanic activity, as has been suggested for non-sorted polygons in this region. These landforms indicate that (i) a long-lived, geologically recent, active cryoturbation layer of ground ice was present in the regolith, (ii) there was some degree of freeze-thaw, and thus (iii) there were sustained period(s), likely within the last 10 Ma, in which the martian climate was 40 to 60 K warmer than current models predict. 相似文献
80.
C. L. Poppett J. R. Allington-Smith G. J. Murray 《Monthly notices of the Royal Astronomical Society》2009,399(1):443-452
We explore the use of remapping techniques to improve the efficiency of highly multiplexed fibre systems for astronomical spectroscopy. This is particularly important for the implementation of diverse field spectroscopy (DFS) using highly multiplexed monolithic fibre systems (MFS). DFS allows arbitrary distributions of target regions to be addressed to optimize observing efficiency when observing complex, clumpy structures such as protoclusters which will be increasingly accessible to extremely large telescopes. We show how the adoption of various types of remapping between the input and output of an MFS can allow contiguous regions of spatial elements to be selected using only simple switch arrays. Finally, we show how this compares in efficiency with integral-field and multi-object spectroscopy by simulations using artificial and real catalogues of objects. With the adoption of these mapping strategies, DFS outperforms other techniques when addressing a range of realistic target distributions. These techniques are also applicable to biomedical science and were in fact inspired by it. 相似文献