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To study the characteristic features of the in-plane free-field response, two actual sites of nuclear power plants, a soft and a rock site, are analysed, by varying the location of the control point and the nature of the wave pattern. Harmonic and transient seismic excitations are examined. The conclusions reached in the vast parametric study of Reference 6 are confirmed for the actual sites. These apply to the range of possible apparent velocities and the associated motions, the spatial variations with depth and in the horizontal direction. If only one component of the control motion, e.g. the horizontal, is matched, then it can be associated either with a body wave or with a surface wave. In the latter case, a specific mode is used up to the frequency at which the next higher mode starts, since for a given frequency, the higher modes attenuate less. The other component of the motion follows. If both components are prescribed, the motion can be interpreted as arising from a combination of a P- and an SV-wave (with a common apparent velocity). Surface waves alone cannot be used to match both components. A body wave has to be included, at least up to the frequency at which the second mode starts. For the soft site, the surface waves decay significantly, especially in the range of higher frequencies, where the apparent velocity is considerably smaller than the shear-wave velocity of the rock. For this site, it seems sufficient to examine only (extremely shallow) body waves. For a rock site, however, Rayleigh-waves exist which attenuate little, leading to smaller apparent velocities than extremely shallow body waves. 相似文献
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Daniel Okoh Jarken Esimbek Jian Jun Zhou Xin Di Tang Augustine Chukwude Johnson Urama Pius Okeke 《Astrophysics and Space Science》2014,350(2):657-681
Intriguing work on observations of 4.83 GHz formaldehyde (H2CO) absorptions and 4.87 GHz H110α radio recombination lines (RRLs) towards 6.7 GHz methanol (CH3OH) maser sources is presented. Methanol masers provide ideal sites to probe the earliest stages of massive star formation, while 4.8 GHz formaldehyde absorptions are accurate probes of physical conditions in dense (103–105 cm?3) and low temperature molecular clouds towards massive star forming regions. The work is aimed at studying feature similarities between the formaldehyde absorptions and the methanol masers so as to expand knowledge of events and physical conditions in massive star forming regions. A total of 176 methanol maser sources were observed for formaldehyde absorptions, and formaldehyde absorptions were detected 138 of them. 53 of the formaldehyde absorptions were newly detected. We noted a poor correlation between the methanol and formaldehyde intensities, an indication that the signals (though arise from about the same regions) are enhanced by different mechanisms. Our results show higher detection rates of the formaldehyde lines for sources with stronger methanol signals. The strongest formaldehyde absorptions were associated with IRAS sources and IRDCs that have developed HII regions, and that do not have EGOs. 相似文献
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East African food security as influenced by future climate change and land use change at local to regional scales 总被引：3，自引：0，他引：3
Nathan Moore Gopal Alagarswamy Bryan Pijanowski Philip Thornton Brent Lofgren Jennifer Olson Jeffrey Andresen Pius Yanda Jiaguo Qi 《Climatic change》2012,110(3-4):823-844
Climate change impacts food production systems, particularly in locations with large, vulnerable populations. Elevated greenhouse gases (GHG), as well as land cover/land use change (LCLUC), can influence regional climate dynamics. Biophysical factors such as topography, soil type, and seasonal rainfall can strongly affect crop yields. We used a regional climate model derived from the Regional Atmospheric Modeling System (RAMS) to compare the effects of projected future GHG and future LCLUC on spatial variability of crop yields in East Africa. Crop yields were estimated with a process-based simulation model. The results suggest that: (1) GHG-influenced and LCLUC-influenced yield changes are highly heterogeneous across this region; (2) LCLUC effects are significant drivers of yield change; and (3) high spatial variability in yield is indicated for several key agricultural sub-regions of East Africa. Food production risk when considered at the household scale is largely dependent on the occurrence of extremes, so mean yield in some cases may be an incomplete predictor of risk. The broad range of projected crop yields reflects enormous variability in key parameters that underlie regional food security; hence, donor institutions’ strategies and investments might benefit from considering the spatial distribution around mean impacts for a given region. Ultimately, global assessments of food security risk would benefit from including regional and local assessments of climate impacts on food production. This may be less of a consideration in other regions. This study supports the concept that LCLUC is a first-order factor in assessing food production risk. 相似文献
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Using the example of the Geff Alternative Site in Wayne County, Illinois, for the disposal of low-level radioactive waste, this paper demonstrates, from a policy and public opinion perspective, the importance of accurately determining site stratigraphy. Complete and accurate characterization of geologic materials and determination of site stratigraphy at potential low-level waste disposal sites provides the frame-work for subsequent hydrologic and geochemical investigations. Proper geologic characterization is critical to determine the long-term site stability and the extent of interactions of groundwater between the site and its surroundings. Failure to adequately characterize site stratigraphy can lead to the incorrect evaluation of the geology of a site, which in turn may result in a lack of public confidence. A potential problem of lack of public confidence was alleviated as a result of the resolution and proper definition of the Geff Alternative Site stratigraphy. The integrity of the investigation was not questioned and public perception was not compromised. 相似文献
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Kirui Pius Oiro Samson Waithaka Hunja Odera Patroba Riedel Björn Gerke Markus 《Natural Hazards》2022,111(1):213-237
Natural Hazards - Himalayan mountains are one of the most seismo-tectonically active zones on the surface of the earth. Recurring moderate and high magnitude earthquakes are not uncommon in this... 相似文献
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To identify the key features of the free-field response for inplane motion, a vast parametric study is performed, varying the location of the control point, the nature of the wave pattern and the site properties. Harmonic excitation for a site consisting of a layer on bedrock is investigated. The nature of the wave pattern producing the site response is classified with respect to the apparent velocity of the motion propagating horizontally across the site. When the control point is selected at the outcrop of the bedrock, the amplification of the motion to the free surface of the site depends on the angle of incidence of the incoming wave in the bedrock. The amplification of the vertical motion for incident P-waves hardly depends (with a tendency of being somewhat larger compared to vertical incidence) on the angle of incidence in the bedrock. The amplification of the horizontal motion for incident SV-waves is affected strongly by the angle of incidence, being larger or smaller than for vertical incidence. Interpreting the two components of the motion at the free surface as arising from a combination of incident P- and SV-waves leads to amplifications within the site (for the horizontal and vertical directions) which do not depend, from a practical point of view, on the angle of incidence and on the prescribed motion up to the fundamental frequency in the horizontal and vertical directions, respectively. The variation of the motion for the first Rayleigh-mode with depth in the two directions bears comparison, in general, with that of vertically incident waves up to the corresponding fundamental frequency. The higher Rayleigh-modes lead to a completely different variation with depth. In contrast to Rayleigh-waves the attenuation of the motion in the horizontal direction for inclined body waves depends on the damping of only the bedrock. Rayleigh-waves thus attenuate more strongly than body waves, especially in the higher-frequency range. Generally, higher Rayleigh-modes attenuate less than the first. 相似文献
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