Statistical estimation of corner frequency and its application to seismic event-identification     

G.R. Dargahi-Noubary 《Soil Dynamics and Earthquake Engineering》1998,17(5):297-309

A statistical method is proposed for estimation of the corner frequency. It is based on inference for a stochastic model whose short-term behavior resembles the established source time functions. Properties of the estimates are investigated and some numerical examples are presented. A discussion concerning earthquake–explosion discrimination and the way corner frequency can be related to the rate of zero-crossings is also included. The paper is concluded with some numerical examples.  相似文献   

On the relative performance of spectrum superposition methods considering modal interaction effects     

R.G. Joshi  I.D. Gupta 《Soil Dynamics and Earthquake Engineering》1998,17(6):357-369

The contribution of modal interaction in the various available spectrum superposition methods is accounted via the modal cross-correlation coefficient, which has been defined in several different approximate ways. Further, in these methods, to define the final expressions directly in terms of the response spectrum amplitudes, the peak factors for all the modal responses are approximated to be equal to the peak factor for the total structural response. However, these assumptions have been found to be violated significantly in many cases and do not hold good in general. Therefore, some recent studies have attempted to improve upon these assumptions. In this paper, detailed investigations are made to study the relative performance of the various available methods considering the modal interaction effects. To find out which of the available methods, in general, gives the better results, the response of a five-storey asymmetric hypothetical building, characterized by significant interaction effects, has been computed from different methods for several widely differing input excitations and the results have been compared with the exact time-history solution.  相似文献   

Enhancing the relative Fe-to-proton abundance in ultra-high-energy cosmic rays     

Carl BlaksleyEtienne Parizot 《Astroparticle Physics》2012,35(6):342-345

We study a generic class of models for ultra-high energy cosmic ray (UHECR) phenomenology, in which the sources accelerate protons and nuclei with a power-law spectrum having the same index, but with different values for the maximum proton energies, distributed according to a power-law. We show that, for energies sufficiently lower than the maximum proton energy, such models are equivalent to single-type source models, with a larger effective power law index and a heavier composition at the source. We calculate the resulting enhancement of the abundance of nuclei, and find typical values of a factor 2-10 for Fe nuclei. At the highest energies, the heavy nuclei enhancement ratios become larger, and the granularity of the sources must also be taken into account. We conclude that the effect of a distribution of maximum energies among sources must be considered in order to understand both the energy spectrum and the composition of UHECRs, as measured on Earth.  相似文献   

The far-ultraviolet albedo of Šteins measured with Rosetta-ALICE     

Michael F. A’Hearn  Lori M. Feaga 《Planetary and Space Science》2010,58(9):1088-1096

During Rosetta’s flyby of the asteroid (2867) Šteins in 2008, we used the ALICE instrument to measure the first far-ultraviolet (FUV) reflectivity spectrum of an asteroid (850-2000 Å). It is very dark in the FUV, ∼4%, compared to its very high reflectivity (40%) at optical wavelengths. The FUV albedo does not exhibit a systematic color trend across the spectral range, but there is a broad absorption feature, not yet identified with a specific mineral, with maximum depth near 1650 Å. The shape of this feature implies a very low abundance of Fe²⁺ ions in the surface minerals. The FUV brightness exhibits a significant opposition surge at phases below 10°. The visible/FUV color gets much redder with increasing phase angle inside the opposition surge and gets gradually redder at larger phase angles. We also conducted a deep search for an exosphere of atoms sputtered from the surface and set upper limits on any column densities of oxygen and hydrogen atoms at the time of our observations. The upper limit for H is comparable to that predicted by the only theoretical prediction of which we are aware, while that for O is higher than predicted by about an order of magnitude.  相似文献   

基于多相滤波器的宽带射电频谱仪设计     

陈林杰  颜毅华  刘飞  王威 《天文研究与技术》2010,7(2)

提出了一种基于多相滤波器的新型宽带射电频谱仪的设计方案。通过多相滤波器实现宽带射电信号的滤波,对滤波后的基带信号进行数字功率检波,再通过积分控制,最终得到射电信号的频谱强度。仿真分析表明,这一设计具有很好的效果,通过多相滤波器,使信号的速率大为降低,克服了传统频谱仪以及采用FFT实现频谱变换方法的缺点,可以实现对超宽带射电信号的实时频谱分析。  相似文献   

一次多回击闪电过程的物理特性分析   总被引：1，自引：0，他引：1  

瞿海燕  袁萍  张廷龙  郄秀书  张义军  张广庶 《高原气象》2012,31(1):218-222

利用西藏那曲无狭缝光栅摄谱仪获得的一次多回击云对地闪电光谱,研究了各放电通道的温度及其变化。结果表明,一次闪电不同回击过程的通道温度有明显差异,闪电前期的温度通常较高,之后呈逐渐降低趋势。将闪电光谱与同步电学观测资料相结合,讨论了光谱特征、通道温度与闪电放电特性、电流热效应的相关性。数据分析显示,光谱总强度与辐射电场的变化幅度成正比;光谱总强度与放电电流的大小成正比;通道温度与回击过程传输的能量为正相关。  相似文献