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张晓晖 《成都信息工程学院学报》2002,17(3):166-169
通过对影响能见度的因素的分析,提出了一种能见度预报方法-综合分析法,极大地提高了能见度的预报准确率。 相似文献
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THECONSTRUCTIONANDITSDEVELOPMENTOFTHEOVERSEASTRANSPORTSYSTEMINNORTHEASTCHINAGaoShali(高莎丽)(DepartmentofGeography,NortheastNorm... 相似文献
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The sand–loess transition zone in north China is sensitive to climate change, and is an ideal place to investigate past environmental changes. However, past climate change at millennial–centennial timescales in this region has not been well reconstructed because of limited numerical dating. Alternations of sandy loam soils with aeolian sand layers in the Mu Us and Otindag sand fields, which lie along the sand–loess transition zone, indicate multiple intervals of dune activity and stability. This change is probably a response to variations of the East Asian monsoon climate during the late Quaternary. The single aliquot regeneration (SAR) optically stimulated luminescence (OSL) dating protocol, which has been successfully applied to aeolian deposits worldwide, is applied to these two sand fields in this study. The OSL ages provide reliable constraints for reconstruction of past climate changes at suborbital timescale. Sections in both sand fields contain aeolian sand beds recording millennial‐scale episodes of dry climate and widespread dune activation, including episodes at about the same time as Heinrich Event 5 and the Younger Dryas in the North Atlantic region. These results demonstrate the potential of aeolian sediments in semi‐arid north China to record millennial‐scale climatic events, and also suggest that dry–wet climate variation at the desert margin in China may be linked to climatic change elsewhere in the Northern Hemisphere, through atmospheric circulation. This article was published online on 27 November 2008. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected (16 December 2008). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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R. J. Protheroe 《Monthly notices of the Royal Astronomical Society》2003,341(1):230-238
I re-examine the brightness temperature problem in PKS 0405-385, which is an extreme intra-day variable radio quasar with an inferred brightness temperature of ∼5 × 1014 K at 5 GHz, well above the Compton catastrophe limit of ∼1011 K that is reached when the synchrotron photon energy density exceeds the energy density of the magnetic field. If one takes into account the uncertainty in the distance to the ionized clouds responsible for interstellar scintillation causing rapid intra-day variability in PKS 0405-385, it is possible that the brightness temperature could be as low as ∼1013 K at 5 GHz, or even lower. The radio spectrum can be fitted by optically thin emission from mono-energetic electrons, or an electron spectrum with a low-energy cut-off such that the critical frequency of the lowest energy electrons is above the radio frequencies of interest. If one observes optically thin emission along a long narrow emission region, the average energy density in the emission region can be many orders of magnitude lower than calculated from the observed intensity if one assumed a spherical emission region. I discuss the physical conditions in the emission region and find that the Compton catastrophe can then be avoided using a reasonable Doppler factor. I also show that MeV to 100-GeV gamma-ray emission at observable flux levels should be expected from extreme intra-day variable sources such as PKS 0405-385. 相似文献
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J. C. B. Papaloizou 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):53-83
We consider orbital resonances in multiplanet systems. These are expected to arise during or just after formation in a gaseous disc. Disc–planet interaction naturally produces orbital migration and circularization through the action of tidal torques which in turn may lead to an orbital resonance. The mass and angular momentum content of the disc is likely to be comparable to that in the planets so that it is essential to fully incorporate the disc in the analysis.We study the orbital evolution of two planets locked in 2:1 commensurability through migration tidally induced by the disc using both analytic methods and numerical hydrodynamic simulations. The planets are assumed to orbit in an inner cavity containing at most only a small amount of disc material. Results are found to be sensitive to initial surface density profile, planet masses and disc parameters. The evolution may range between attaining and subsequently maintaining a resonance lock with two angles librating to divergent migration with no commensurability formed. In the former case eccentricities increase monotonically with time while the system undergoes inward migration. If the migration is halted by loss of the disc leaving the planets in a final configuration, there is likely to be a low probability of seeing resonant planets at small radii as well as a sensitive dependence on past history.We have also considered a multiplanet system in secular apsidal resonance. We consider the system as being in just one secular normal mode and include the effects of a gaseous disc. It is suggested that a normal mode may be selected by adding in some weak dissipative process in the disc and that it may remain, involving only the planets, when the disc is slowly removed. 相似文献
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基于CTI技术的守时系统故障报警实现 总被引:2,自引:0,他引:2
介绍了计算机电话集成(CTI-Computer Telephony Integration)技术在守时系统故障自动报警中的应用。简要介绍了构成报警系统的两个关键产品,电话语音卡和TTS(Text-To-Speech),详细讨论了ActiveX控件(Phonic.OCX)编程接口的一系列事件和方法以及由此而开发的故障报警模块。该模块不仅用于守时主系统的故障报警,也将用于电源系统、钟房环境监控系统的故障报警。 相似文献
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