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61.
电路参数随时间变化的介观LC电路的波函数和压缩效应 总被引:2,自引:0,他引:2
本文通过正则变换,采用路径积分的方法,得出了电路参数随时间变化的介观LC电路的严格波函数,研究了含时相干态下电路中电荷和电流的压缩效应。 相似文献
62.
航空发动机的高温蠕变分析 总被引:6,自引:0,他引:6
详述了航空发动机主要零部件抗蠕变的设计要求 ,综合概括了有关蠕变的设计准则和计算分析方法以及寿命预测方法 相似文献
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S.N.V.S. Prasad P.V.S. Rama Rao D.S.V.V.D. Prasad K. Venkatesh K. Niranjan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
The amplitude scintillations data recorded at 244 MHz from the geostationary satellite, FLEETSAT (73°E) at a low latitude station, Waltair (17.7°N, 83.3°E) during the ten year period of high to low solar activity from 2001 to 2010 is considered to study the occurrence characteristics of the VHF scintillations. A close association between the intense scintillations on VHF signals during pre-midnight hours, associated with range type of spread-F on ionograms and a relatively weak and slow fading scintillations during post-midnight hours associated with frequency type of spread-F is observed during the relatively high sunspot years from 2001 to 2004, whereas during the low sunspot years from 2005 to 2010 the scintillation activity as well as spread-F activity are found to be minimum. During both the high and low sunspot years, it is observed that the maximum scintillation activity occurs during equinoctial months followed by winter with the minimum occurrence during summer months. The annual mean percentage occurrence of scintillations is found to be clearly associated with the variations in the annual mean sunspot number. The nocturnal variations in the occurrence of scintillations show the onset of scintillation activity starts from 19:00 h LT with maximum of occurrence around 21:00 h LT. A clear semiannual variation in the occurrence of scintillations is observed during pre-midnight hours with two peaks in equinoctial months of March/April and September/October. The number of scintillation patches observed is found to be more during pre-midnight hours compared to those during post-midnight hours. The most probable scintillation patch duration lies around 30 min. Further, it is also found that the number of scintillation patches with durations of 60 min and more decreases with the increase in the patch duration. It is also observed in general that the scintillation activity is inhibited during geomagnetic disturbed days. 相似文献
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B. Spandana S. Srinivasa Rao Adithi R. Upadhya Padmavati Kulkarni V. Sreekanth 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3134-3146
The PM2.5/PM10 ratio (PM2.5 and PM10 are defined as mass concentration of particles having aerodynamic diameter less than 2.5 and 10 µm respectively) is one of the important parameters in understanding the severity of the fine mode surface particulate matter pollution. The present study characterises PM2.5/PM10 ratio estimates from eight Indian urban sites with varying levels of urbanization. Five years (2015–2019) of collocated PM2.5, PM10, and meteorological (ambient temperature, relative humidity (RH), and wind speed) measurements are used to understand the spatial and temporal variability in the PM2.5/PM10 ratio at different scales and to investigate its relationship with meteorological parameters. Over the study sites, the seasonal mean PM2.5/PM10 ratio varied between 0.31 ± 0.08 (mean ± standard deviation) and 0.65 ± 0.13. Seasonally, the highest PM2.5/PM10 ratio was observed during winter and post-monsoon seasons. Sites in the Indo-Gangetic Plain (IGP) exhibited higher PM levels (PM2.5 and PM10) and higher PM2.5/PM10 ratios than the corresponding values recorded at other sites. The seasonal mean PM2.5/PM10 ratio estimated (over the study sites) using MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) ranged between 0.25 ± 0.08 and 0.77 ± 0.16, and exhibited consistent overestimation (when compared to values derived from measurements) during winter and pre-monsoon seasons. Grossly, the PM2.5/PM10 ratio exhibited a weak association with meteorological parameters. Interestingly, despite variations in geography, population, anthropogenic activities and PM concentrations across seasons and sites, the PM2.5/PM10 ratio showed low variability. 相似文献
67.
S.S. Rao Shweta Sharma P. Galav R. Pandey 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Ionosonde data of a mid latitude station Novosibirsk (Geog. Lat. 54.6°N, Geog. Long. 83.2°E) has been analyzed for the years 1997–2006 that covers the major part of solar cycle 23. Our results show the presence of winter anomaly in the daytime F2 layer critical frequency during different phases of solar activity. Results also reveal a semiannual variation of foF2 with two maxima and a minimum that always appears in summer. While the first maximum is in the spring equinox, the second one is found to shift from autumn to winter with the increase of solar activity. The maximum height of F2 layer during the daytime shows variation with the solar activity. It is higher during the higher activity periods and lower during the periods of low activity. Results of ionosonde observations have been compared with those obtained from IRI-2007 model and it is found that model reproduces gross features of foF2 variation. However, the modeled hmF2 variations during equinoxes are significantly different from the ones derived using the ionosonde data. The model also underestimates the hmF2 values. 相似文献
68.
Bartley William C. McCracken Kenneth G. Rao U.R. 《IEEE transactions on aerospace and electronic systems》1967,(2):230-235
This paper describes an aspect system flown on PIONEERS VI and VII2 which incorporates an extremely accurate adaptive digital computer in order to define rigorously equal time intervals which are submultiples of the spacecraft spin period. The several submultiples which compose the complete spin period exhibit equality to within 2.5 parts in 105. This system has potential applications in other experiments involving the study of the angular dependence of cosmic radiation and other physical phenomena being measured by a single directional detector mounted on spin-stabilized spacecraft. Included here are the scientific goals for this experiment, system restraints, and the generalized system operation. Some details on specific logic and hardware implementation for the Pioneer experiments are included along with in-flight performance evaluation of the system aboard PIONEER VI. 相似文献
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Technological advances in remote sensing capabilities, wider participation of commercial firms and the possibilities of ‘processing’ spatial data to create value-added information have given rise to a range of policy and legal issues in the geographic information (GI) field. How far satellite images can still be considered a ‘public good’, conflicts between commercial and national interests is becoming a major issue, especially where security is concerned, sovereignty and the rights of sensed states, shutter control vs transparency is debated, data access, IPR and infringement of privacy becoming more relevant are all discussed. At the same time, the societal and public good of GI is well accepted with innumerable national and international examples. It is clear that societies would greatly benefit from the proper use of GI. A multilateral debate to formulate a GI policy that will take account of these while ensuring that the full benefits of remote sensing are available to society is called for. 相似文献