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41.
For decades, ground-based radio observations of Jovian synchrotron radiation have shown emission originating predominantly from the equatorial region and from high-latitude regions (lobes) near L∼2.5. The observations show a longitudinally asymmetric gap between the emission peaks of the lobes and the atmosphere of Jupiter. One possible explanation for these gaps is the loss of electrons through collisions with atmospheric neutrals as the electrons bounce along magnetic field lines and drift longitudinally in the presence of asymmetric magnetic fields. To assess this hypothesis, we applied the recently developed O6 and VIP4 magnetic field models to calculate the trajectories of electrons as they drift longitudinally in Jupiter's magnetic field, and derive the sizes of their equatorial drift loss cones. We then identified the shells on which electrons would be lost due to collisions with the atmosphere. The calculated drift loss cone sizes could be applied in future to the modeling of electron distribution functions in this region and could also be applied to the study of Jovian auroral zone. This method also allowed us to compute the shell-splitting effects for these drifting electrons and we find the shell-splitting to be small (?0.05RJ). This justifies a recent modeling assumption that particles drift on the same shells in a three-dimensional distribution model of electrons. We also compared the computed gaps with the observed gaps, and found that the atmospheric loss mechanism alone is not able to sufficiently explain the observed gap asymmetry. 相似文献
42.
BRAUNSTEIN M. COMSTOCK R. HOFFMAN P. WOMACK M. DEGLMAN F. PINNICK D. AAKER G. GOLDSCHEN M. JACOBSON A. ZILKA J. FAITH D. MOORE S. RICOTTA J. WEIST A. MODI C. 《Earth, Moon, and Planets》1997,78(1-3):219-227
An optical archive of comet Hale-Bopp was obtained over 28 nights from June 1996 to May 1997 covering a range of heliocentric
distances of r = 4.12 − 0.91. The CCD images were obtained with the 0.8-m University of Washington Manastash Ridge Observatory
and the 0.25-m Pennsylvania State University at Eriemobile observatory. The reduced images clearly document the evolution
of features of the coma, which were dominated by radial jetsfrom r = 4.1 − 2.3 AU, curved fan-shaped jets from r = 1.2 − 1.0
AU, and arcs or shells for 0.9 < r < 1.0 AU. We present the images and derive an average dust expansion velocity of Vdust = 0.67 ± 0.07 km s−1 from measurements of the arc features. The images in thearchive will be made available to other researchers for further study.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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LAI Zhongping 《《地质学报》英文版》2014,(Z1)
正A geological feature in the Qaidam Basin known as the"Shell Bar"contains millions of freshwater articulated clam shells buried in-situ.Since the 1980s this feature in the now hyper-arid basin has been interpreted to be lake deposits that provide evidence for a warmer and more humid climate than present during late Marine Isotope Stage 3(MIS 3)(Bowler et al.,1986).However,the global climate during 相似文献
45.
浮游有孔虫壳体Mg/Ca值--SST的替代性指标 总被引:5,自引:0,他引:5
通过对东北印度洋区MD77181和MD81349两支岩心中Globigerinoides sacculifer壳体极为精细的清洗和溶样后,由ICP—MS测试获得了近260ka以来Mg/Ca值.结果表明Mg/Ca值与δ^18O值变化趋势较为吻合,随温度的增加而升高,浮游有孔虫G.sacculifer壳体Mg/Ca值是海洋表层水温(SST)良好的替代性指标.运用函数式Mg/Ca=0.4717exp(0.0825*SST)计算表明,包括印度洋在内的中、低纬地区,LGM时期的SST与全新世的温差大于最初CLIMAP推测的2℃,很可能达到4℃. 相似文献
46.
本文从石英包裹体的气液相成分分析数据和均一温度测定结果出发,计算出矿床的成矿压力、成矿热液的物理比学参数及其化学成分特征参数。结合矿床地质特征对矿床的成矿温度、矿床成矿热液的性质和来源、热液的流动方向、热液化学成分与金矿化的关系、热液中金的迁移形式和沉淀机制等问题作了进一步地探讨。结果表明,安家岔金矿床具有改造型金矿床的成因特点。 相似文献
47.
Manzini Federico Crippa Roberto Oldani Virgino Guaita Cesare 《Earth, Moon, and Planets》1999,87(2):73-85
Using a CCD camera attached to the 0.335 m and 0.20 m reflectors of S.A.S. Observatory (Novara, Italy), we followed the linear
jets and shells of comet Hale–Bopp between May 1996 and May 1997. In addition to confirming the model of Sekanina and Bohenhardt
(1997), the study of the linear jets provided indications concerning the orientation of the comet's axis of rotation over
time. The study of the shells revealed that the speed at which they move away from the nucleus was not constant. A periodic
variation of the shell expansion velocity may not be excluded : if so, a possible precessional effect on the axis of rotation
of the comet's nucleus could explain this behavior.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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50.
Richard G. West Karen L. Knudsen David N. Penney Richard. C. Preece J. Eric Robinson 《第四纪科学杂志》1994,9(4):357-366
Assemblages of foraminifers, ostracods and molluscs from temperate Ipswichian Stage (last temperate stage) sediments and overlying cold Devensian Stage (last cold stage) sediments at Somersham in the southern Fenland of Cambridgeshire have been analysed. The Ipswichian sediments contain faunas consistent with temperate brackish water conditions under tidal influence. The Devensian assemblages were recovered from a series of sands and gravels laterally accreting in a channel cutting into Ipswichian sediments. In contrast to the Ipswichian faunas, the faunas of particular Devensian samples show a complex mixture of temperate freshwater, brackish and marine taxa. The molluscs are mainly freshwater, with few land snails; they occur together with foraminifers and ostracods. Freshwater, brackish water and marine ostracods are present with foraminifers. A sample of Devensian fine laminated sediment in the channel was analysed for pollen; only abundant pre-Quaternary spores were present, with abundant foraminifers in the same sample. The taphonomy of the assemblages and the difficulties of their interpretation in environmental terms are discussed. The importance of taphonomy in assessing environments, climate, range of taxa and dating is stressed. 相似文献