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排序方式: 共有513条查询结果,搜索用时 15 毫秒
311.
本文利用美国喷气动力实验室(JPL)提供的电离层总电子含量(TEC)的地图网格产品,计算了中国区域上空电离层TEC与月均值偏差及其空间相关系数矩阵,从而分析了TEC与月均值偏差空间相关性的分布特征,根据统计学中定义的相关距离提取了这种偏差在经、纬度方向上的空间特征尺度.并以2008年和2011年为例,着重考察了TEC月偏差的空间特征尺度与太阳活动水平、地磁条件和季节变化之间的关系.结果发现,TEC与月均值偏差的空间相关性呈现椭圆形高斯分布的特征,沿纬线方向的特征尺度大于沿经线方向,不同纬度区域偏差的空间相关性特征差异明显,高纬的特征尺度在两个方向上均小于低纬,而不同经度区域在相同地方时条件下表现差异不大;两个方向的特征尺度在白天、太阳活动水平高和地磁活动剧烈时均存在增大的现象. 相似文献
312.
K.-H. Fornacon H. U. Auster E. Georgescu W. Baumjohann K.-H. Glassmeier G. Haerendel J. Rustenbach M. Dunlop 《Annales Geophysicae》1999,17(12):1521-1527
The special feature of the ringcore fluxgate magnetometer on Equator-S is the high time and field resolution. The scientific aim of the experiment is the investigation of waves in the 10–100 picotesla range with a time resolution up to 64 Hz. The instrument characteristics and the influence of the spacecraft on the magnetic field measurement will be discussed. The work shows that the applied pre- and inflight calibration techniques are sufficient to suppress spacecraft interferences. The offset in spin axis direction was determined for the first time with an independent field measurement by the Equator-S Electron Drift Instrument. The data presented gives an impression of the accuracy of the measurement. 相似文献
313.
Human space flight represents a heady mix of bravery and drama which can be inspirational to nations and to humankind but
at huge economic cost. Due to the current high launch costs only a handful of people have ventured beyond low Earth orbit
and walked on the Moon, propelled by aspirations related more to the Cold War than to science. Problems with reusable launch
vehicle development mean that severe launch cost limitations will exist for some time. Meanwhile, cheaper robotic probes have
visited all the planets except Pluto, flown by comets, landed on Mars, Venus and an asteroid, have probed Jupiter's atmosphere
and studied the Universe beyond our own solar system with telescopes. Using these data we are determining mankind's place
in the Universe. Public interest in the historic Eros landing eclipsed a simultaneous space walk at the fledgling International
Space Station and the Mars Pathfinder landing generated hundreds of millions of website hits in a few days. Given the fact
that hundreds of Mars missions could be flown for the still-escalating cost of the International Space Station, the unsuitability
of human bodies for deep space exploration, and the advances in 3-d and virtual reality techniques, we discuss whether human
exploration needs a place in a realistic, useful and inspirational space programme.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
314.
During the eighties, microgravity research focussed predominantly on the investigation of fundamental phenomena, often with
limited industrial support. Although this approach led to some rather impressive breakthroughs in terms of new theoretical
insights and microgravity experimentation, the need for increased co-ordination and interest from industry became increasingly
apparent. In this decade, a user-driven research strategy has been instigated by ESA to promote microgravity research. The objective is to coordinate ESA, national
activities and industry into an overall European strategy, which will allow valuable application-oriented microgravity research
to be performed aboard the International Space Station (ISS). On this basis, it is expected that scientific progress will
evolve even more rapidly due to the easier planning, regular access and longer experiment-durations associated with the ISS.
This paper highlights the wealth of microgravity research being co-ordinated by ESA in the field of physical sciences. A number of key areas of research under microgravity conditions are currently being explored such as alloy solidification,
crystal growth,measurement of thermophysical properties, combustion mechanisms, fluid flow, cold atom physics and complex
plasmas, to name but a few. The following sections will provide background information relating to the various ESA research
programmes, as well as emphasising their microgravity relevance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
315.
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317.
For the first time during the mission, the Anisotropy Telescopes instrument on board the Ulysses spacecraft measured constant zero anisotropy of protons in the 1.3/2.2 MeV energy range, for a period lasting more than three days. This measurement was made during the energetic particle event taking place at Ulysses between 25 November and 15 December 1998, an event characterised by constant high proton fluxes within a region delimited by two interplanetary forward shocks, at a distance of 5.2 AU from the Sun and heliographic latitude of 17°S. We present the ATs results for this event and discuss their possible interpretation and their relevance to the issue of intercalibration of the two telescopes. 相似文献
318.
319.
用双线偏振雷达研究云内粒子相态及尺度的空间分布 总被引:20,自引:5,他引:20
本文用中国科学院兰州高原大气物理研究所平凉雷达站的C波段双线偏振雷达的层状云、对流云的观测资料,结合不同粒子的生长规律及对C波段雷达波的散射特性的研究,用ZDR参量系统分析并解释了层状云、对流云内粒子相态及尺度的空间分布规律。从中发现:在发展旺盛的对流云中ZDR>3.0dB的区域经常会延伸到4km以上,这些区域可能存在过冷水滴和扁状冰相粒子,而这些粒子的存在与对流云的发展有一定的关系。零度层以下层状云ZDR的突增和实减反映了冰相粒子融化形成大雨滴然后大雨滴破碎的规律。冰雹云中负的ZDR与冰雹的取向和尺度有关。这一工作代表了中国双线偏振雷达最新研究成果,它证明了双线偏振雷达在研究云微物理机制方面优于普通雷达,双线偏振雷达为研究云的发展机制、人工影响天气指挥及效果检验提供了新的手段,这一结果也为该技术在中国的推广提供了有利的依据。 相似文献
320.
Jose Morales Alfred Stein Johannes Flacke Jaap Zevenbergen 《International journal of geographical information science》2020,34(7):1451-1474
ABSTRACT Spatial information of land values is fundamental for planners and policy makers. Individual appraisals are costly, explaining the need for predictive modelling. Recent work has investigated using Space Syntax to analyse urban access and explain land values. However, the spatial dependence of urban land markets has not been addressed in such studies. Further, the selection of meaningful variables is commonly conducted under non-spatialized modelling conditions. The objective of this paper is to construct a land value map using a geostatistical approach using Space Syntax and a spatialized variable selection. The methodology is applied in Guatemala City. We used an existing dataset of residential land value appraisals and accessibility metrics. Regression-kriging was used to conduct variable selection and derive a model for spatial prediction. The prediction accuracy is compared with a multivariate regression. The results show that a spatialized variable selection yields a more parsimonious model with higher prediction accuracy. New insights were found on how Space Syntax explains land value variability when also modelling the spatial dependence. Space Syntax can contribute with relevant spatialized information for predictive land value modelling purposes. Finally, the spatial modelling framework facilitates the production of spatial information of land values that is relevant for planning practice. 相似文献