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Bigg Grant R. Cropper T. E. O’Neill Clare K. Arnold Alex K. Fleming A. H. Marsh R. Ivchenko V. Fournier Nicolas Osborne Mike Stephens Robin 《Natural Hazards》2018,92(2):1113-1136
Natural Hazards - With the polar regions opening up to more marine activities but iceberg numbers more likely to increase than decline as a result of global warming, the risk from icebergs to... 相似文献
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J. P. Osborne 《Astrophysics and Space Science》1987,130(1-2):207-223
The X-ray observatory EXOSAT spent over 1000 hours observing cataclysmic variables. Some of the major results reviewed here are: soft X-ray light curve changes in AM Her objects, orbital effects in the X-ray light curves of intermediate polars and U Gem, regular behaviour in the inter-outburst X-ray flux of VW Hyi, and X-ray emission from the tenuous remnant of the recent recurrent nova RS Oph. The ability of EXOSAT to make long uninterupted observations at high sensitivity over a broad spectral range and to react quickly to cosmic events has yielded a dataset of a quality that will not be surpassed for many years.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986. 相似文献
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A. P. Beardmore K. Mukai A. J. Norton J. P. Osborne & C. Hellier 《Monthly notices of the Royal Astronomical Society》1998,297(2):337-347
Comparison of five X-ray observations of the intermediate polar FO Aqr reveals that the morphology of the X-ray light curve changes considerably with time. In particular, power spectra of the 1988 Ginga and 1993 ASCA data reveal strong sideband and orbital variations, whereas the 1990 Ginga observation does not. This suggests that the amount of stream-fed accretion varies with epoch, and the system was accreting predominantly from a disc in 1990. In contrast to other intermediate polars, the X-ray spin-pulse profiles show significant variations between observations, ranging from relatively sinusoidal to sawtooth-shaped at medium energies. During the 1988 and 1990 observations a notch is visible at spin phase zero, due to the presence of an interpulse at phase 0.85, which is absent during the other observations. At lower energies a narrow pulse of emission is seen at spin phase 0.2. We interpret the pulse profile from the 1990 Ginga observation using a model for accretion from a disc on to a dipolar magnetic field, the axis of which is offset from the white dwarf centre by ∼ 0.15 white dwarf radii. In order to account for the later occurrence of the hardness-ratio maximum in 1988 and 1993, we suggest that the accretion-rate profile changes so that accretion is favoured along the field lines which trail the magnetic pole. This also accounts for the disappearance of the interpulse and notch in 1993. 相似文献
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The Late Devensian-Flandrian transition depicted by serial insect faunas from West Bromwich, Staffordshire, England 总被引:1,自引:0,他引:1
A bed of peat resting on sands and gravels and reaching the present-day ground surface, was investigated for beetles, and seven radiocarbon dates were obtained. The beetles indicated that the lowest layers of the peat, dated around 12,000 B.P., were laid down in boggy conditions in a treeless landscape under a climatic regime which was rather cooler than present day. Two quite sudden changes in the aspect of the fauna then followed. The first was the incoming of an assemblage indicative of a climate of arctic severity. This layer was not dated but if the rate of deposition was constant during this period it must have been around 11,000 B. P. The second change was the equally rapid disappearance of this northern fauna about 1000 years later. Succeeding layers then contained beetles suggesting conditions as warm as those of the present day, with species indicating both coniferous and deciduous trees appearing before 9500 B.P. 相似文献