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91.
Selection of ground motion time series and limits on scaling 总被引:4,自引:0,他引:4
Jennie Watson-Lamprey Norman Abrahamson 《Soil Dynamics and Earthquake Engineering》2006,26(5):477-482
A procedure to select time series for use in non-linear analyses that are intended to result in an average response of the non-linear system is proposed that is not based simply on magnitude, distance, and spectral shape. A simple model of a yielding system is used as a proxy for the non-linear behavior of a more complicated yielding system. As an example, Newmark displacements are used as a proxy for more complex slope-stability models. The candidate scaled time series are evaluated to find those that yield a response of the simple non-linear system that is near the expected response for the design event. Those scaled time series with responses near the expected value are selected as the optimum time series for defining average response even if the scale factors are larger than commonly accepted (e.g. scale factors >factor of 2). 相似文献
92.
93.
Sarah L. Holloway 《Geoforum》2007,38(1):7-20
In the past decade geographers have critiqued the exclusivity of idyllic representations of rurality and sought to explore the diverse experiences of Other social groups in the countryside. This paper builds upon that small but significant strand of research which has highlighted the whiteness of representations of rurality and the consequences of this for racialised minorities. These debates have been crucially important in forwarding our understanding of racially-exclusive constructions of idyllic country living; however, it is important that academics neither assume that such ideas are forever fixed, nor that they affect all minority ethnic groups in the same ways. This paper takes both the potential power and frailty of these ideas seriously, as it examines how the concepts of race, racism and rurality are deployed by different commentators as they debate the place of one specific minority ethnic group in the English countryside. The route taken into this is a consideration of print-media reporting of events in Firle, Sussex, where, in 2003, some white rural residents symbolically purged their village of Gypsy-Travellers by burning a mock caravan complete with effigies at their annual bonfire celebrations. In conclusion, the paper challenges the relative lack of attention to these issues within the white-dominated discipline of geography, and argues that it is imperative to trace the dynamic ways in which the whiteness of idyllic understandings of the rural are reinforced and challenged through contemporary social practice. 相似文献
94.
On the link between GPS pseudorange noise and day-boundary discontinuities in geodetic time transfer solutions 总被引:1,自引:3,他引:1
When neglecting calibration issues, the accuracy of GPS-based time and frequency transfer using a combined analysis of code
and carrier phase measurements highly depends on the noise of the GPS codes. In particular, the pseudorange noise is responsible
for day-boundary discontinuities which can reach more than 1 ns in the time transfer results obtained from geodetic analysis.
These discontinuities are caused by the fact that the data are analyzed in daily data batches where the absolute clock offset
is determined by the mean code value during the daily data batch. This pseudorange noise is not a white noise, in particular
due to multipath and variations of instrumental delays. In this paper, the pseudorange noise behavior is characterized in
order to improve the understanding of the origin of the large day-boundary discontinuities in the geodetic time transfer results.
In a first step, the effect of short-term noise and multipath is estimated, and shown to be responsible for only a maximum
of 150 ps (picoseconds) of the day-boundary jumps, with only one exception at NRC1 where the correction provides a jump reduction
of 300 ps. In a second step, a combination of time transfer results obtained with pseudoranges only and geodetic time transfer
results is used to characterize the long-term evolution of pseudorange errors. It demonstrates that the day-boundary jumps,
especially those of large amplitude, can be explained by an instrumental effect imposing a common behavior on all the satellite
pseudoranges. Using known influences as temperature variations at ALGO or cable damages at HOB2, it is shown that the approach
developed in this study can be used to look for the origin of the day-boundary discontinuities in other stations. 相似文献
95.
《遥感图像处理》课程教学在地理学专业中的探索与实践 总被引:1,自引:0,他引:1
针对地理专业的自身特点和当前遥感图像处理的教学现状,提出了遥感图像处理课程在地理专业中的主要教学内容框架、教学方法以及教学改革方向,并对该课程的实践教学部分做了重点介绍,最后论述了该课程在地理学专业实践教学中的取得一些教改成果。 相似文献
96.
太阳常数的变化与太阳软x射线辐射流量及低频天波时延的关系 总被引:1,自引:0,他引:1
本文对1982年在陕西临潼接收的美国罗兰-C西北大平洋链Y台发射的100kHz低频一跳天波时延的实测资料及SMS-GOES测量的太阳1~8A软x射线的每日辐射流量与SMM/ACRIMI测量的太阳常数之间的关系进行了分析。结果表明:太阳1~8A软x射线辐射流量与太阳常数之间存在较强的负相关;低频一跳天波时延与太阳常数之间存在着较强的正相关。并对此进行了讨论。 相似文献
97.
关于建立我国卫星电视授时系统的方案 总被引:2,自引:1,他引:1
提出搭载现存的卫星TV广播系统进行高精度授时的方案,改进和提高我国的授时服务。该方案与现存的短波、长波授时比较,有许多优点:精度高、复盖面大、用户设备简单,能24小时连续服务,并包含有更多的时间信息、自动定时和输出标准频率。2~3年就能建成本系统.即可以投入使用,且投资很少。 相似文献
98.
毫秒脉冲星计时观测的研究进展 总被引:8,自引:1,他引:7
对毫秒脉冲星时间测量的理论、方法和技术研究的进展进行了阐述。根据近年来取得的观测研究结果,毫秒脉冲星计时测量误差~2×10-7秒,毫秒脉冲星自转周期稳定性足以和现代原子钟相媲美:其相对频率不稳定度达到1×10-14(1年≤γ≤5.2年),并可望更高。近年来,脉冲星计时观测系统的接收灵敏度获得很大改进,计时观测的数据采集、处理技术、脉冲到达时间分析模型研究等都有长足发展。通过综合脉冲星时间算法得到的脉冲星时间尺度将比现代原子时具有更高的长期稳定度。叙述了脉冲星的物理特性及有关计时观测系统的技术成果,如观测频率和带宽的选择,消色散和接收系统灵敏度等问题。最后对毫秒脉冲星时间测量的误差源进行了讨论,并对脉冲星时间尺度的应用前景做了展望。 相似文献
99.
100.
滇-黔-桂微细浸染型金成矿带处于滇-黔-桂裂谷中。金矿床分布与深大断裂存在依附性。金矿带基本展布于深大断裂限定的三角区内,金矿床则分布于深大断裂旁侧或其交叉部位。由幔源岩浆岩(超基性岩及玄武岩)和幔源矿物沿深大断裂分布可推断,深大断裂延伸较深,可达上地幔,属超壳深大断裂。金矿床分布不受地层层位的限制,金矿化具有多层位成矿性。铅、硫、碳、氢、氧同位素地球化学综合对比研究表明,成矿热液中的矿质、矿化剂和水具深源与浅源的混合特征。热液成矿期矿石中石英及萤石的电子自旋共振(ESR)定年结果为68.40±32.41Ma,表明本区金矿床的成矿可能发生在燕山晚期-喜山早期。 相似文献