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971.
V.K.D. Srinivasu N. Dashora D.S.V.V.D. Prasad K. Niranjan S. Gopi Krishna 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(7):1761-1775
This study presents unique perspectives of occurrence and strength of low latitude ionospheric scintillations on multiple signals of Global Navigation Satellite System (GNSS) and its frequency dependence using continuous observation records of 780 nights. A robust comparative analysis is performed using scintillation index, S4 and its variation during pre-midnight and post-midnight duration from a GNSS receiver located at Waltair (17.7°N, 83.3°E), India, covering period from July 2014 to August 2016. The results, generally exhibit the impact of declining phase of solar cycle 24 on occurrence and strength of scintillations, which, however, is evidently different over different frequencies transmitted from different GNSS systems. A deeper quantitative analysis uniquely reveals that apart from the solar cycle and seasonal effects, the number of visible satellites of a selected GNSS markedly affect the occurrence and also the strength. Processing scheme of adopting 6 hourly time windows of pre-midnight and post-midnight brought a novel result that the strength and occurrence of strong scintillations decrease with declining solar activity during pre-midnight hours but remarkably increase for moderate and weak scintillations during post-midnight. The physical processes that dominate the post-midnight equatorial ionosphere are invoked to explain such variations that are special during declining solar activity. Finally, inter-GNSS signal analysis in terms of the effect of strong, moderate and weak scintillations is presented with due consideration of number of satellite passes affected and frequency dependence of mean S4. The quantitative results of this study emphasize for the first time effect of low latitude scintillation on GNSS signals in Indian zone under changing background solar and seasonal conditions. 相似文献
972.
I.A. Molotkov B. Atamaniuk 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The article is devoted to modeling the impact on the ionosphere powerful obliquely incident wave beam. The basis of this analysis will be orbital variational principle for the intense wave beams-generalization of Fermat’s principle to the case of a nonlinear medium (, , and ). Under the influence of a powerful wave beam appears manageable the additional stratification of the ionospheric layer F2. Explicit expressions show how the properties of the test beam, with a shifted frequency, released in the same direction as the beam depend on the intensity of a powerful beam and the frequency shift. 相似文献
973.
Evelyn De Wachter Klemens Hocke Thomas Flury Dominik Scheiben Niklaus Kämpfer Soohyun Ka Jung Jin Oh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The period January–February 2008 was characterized by four Sudden Stratospheric Warmings (SSWs) in the Northern Hemisphere, of which the last warming, at the end of February 2008, was a major warming. A significant decrease in mesospheric water vapour (H2O) of more than 2 ppmv (∼40%) was observed by the ground-based microwave (GBMW) radiometer in Seoul, S. Korea [37.3°N, 126.3°E] during the major SSW. A comparison with ground-based mesospheric H2O observations from the mid-latitude station in Bern [46.9°N, 7°E] revealed an anticorrelation in the mesospheric H2O data during the major SSW. In addition, prior to the major warming, strong periodic fluctuations were recorded in the Aura MLS vertical temperature distribution between 15 and 0.05 hPa at Seoul. The mesospheric temperature oscillation was found to have a period of ∼10–14 days with a persistency of 3–4 cycles. 相似文献
974.
介绍了轧波成形+胀形的工艺过程、设备原理及技术改进.首先用轧波成形制出工件的大概形状,然后再用胀形工艺校圆.该成形方法不仅要求工装简单,而且成形精度较高,适用于旋转环形钣金零件. 相似文献
975.
P.K. Karmakar M. Maiti S. Mondal Carlos Frederico Angelis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The radiosonde data available from British Atmospheric Data Centre (BADC) for the latitudinal occupancy of 58° north through 45° south were analyzed to observe the variation of temperature and water vapor density. These two climatological parameters are largely assumed to be the influencing factors in determining the millimeter wave window frequencies over the chosen range of latitudes in between the two successive maxima occurring at 60 and 120 GHz. It is observed that between temperature and water vapor density, the later one is influencing mostly in determining the window frequency. It is also observed that the minima is occurring at 75 GHz through 94 GHz over the globe during the month January–February and 73 GHz through 85 GHz during the month July–August, depending on the latitudinal occupancy. It is observed that the large abundance of water vapor is mainly held responsible for shifting of minima towards the low value of frequencies. Hence, it is becoming most important to look at the climatological parameters in determining the window frequency at the place of choice. 相似文献
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