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排序方式: 共有167条查询结果,搜索用时 15 毫秒
1.
JoAnn Browning 《地震工程与结构动力学》2002,31(6):1267-1280
A maximum allowable period criterion is used to determine reasonable stiffness requirements for reinforced concrete frames with the seismicity associated with central and eastern U.S. A general relationship is developed to describe the displacement demand expected for central and eastern U.S. based on a survey of available ground motions, opinions of seismologists, and code‐based provisions. A series of hypothetical reinforced concrete frames is proportioned using a maximum allowable period criterion and evaluated for expected maximum displacement response using non‐linear dynamic analyses and a suite of ground motions. Results indicate that for the reinforced concrete structural systems considered in the study, proportioning for gravity loads will provide sufficient stiffness in central and eastern U.S. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
Jeremy C. Ely Chris D. Clark Richard C. A. Hindmarsh Anna L. C. Hughes Sarah L. Greenwood Sarah L. Bradley Edward Gasson Lauren Gregoire Niall Gandy Chris R. Stokes David Small 《第四纪科学杂志》2021,36(5):946-960
Palaeo-ice sheets are important analogues for understanding contemporary ice sheets, offering a record of ice sheet behaviour that spans millennia. There are two main approaches to reconstructing palaeo-ice sheets. Empirical reconstructions use the available glacial geological and chronological evidence to estimate ice sheet extent and dynamics but lack direct consideration of ice physics. In contrast, numerically modelled simulations implement ice physics, but often lack direct quantitative comparison with empirical evidence. Despite being long identified as a fruitful scientific endeavour, few ice sheet reconstructions attempt to reconcile the empirical and model-based approaches. To achieve this goal, model-data comparison procedures are required. Here, we compare three numerically modelled simulations of the former British–Irish Ice Sheet with the following lines of evidence: (a) position and shape of former margin positions, recorded by moraines; (b) former ice-flow direction and flow-switching, recorded by flowsets of subglacial bedforms; and (c) the timing of ice-free conditions, recorded by geochronological data. These model–data comparisons provide a useful framework for quantifying the degree of fit between numerical model simulations and empirical constraints. Such tools are vital for reconciling numerical modelling and empirical evidence, the combination of which will lead to more robust palaeo-ice sheet reconstructions with greater explicative and ultimately predictive power. 相似文献
3.
Dong Zhijie Sasha Meng Lingyu Christenson Lauren Fulton Lawrence 《Natural Hazards》2021,106(3):2077-2109
Natural Hazards - Prediction in ungauged basins (PUB) is as crucial as it is challenging. Thus far, there have been abundant regionalization studies on PUB, whereas "regionalization" is... 相似文献
4.
Lauren Patterson Marie Urban Aaron Myers Budhendra Bhaduri Eddie Bright Phillip Coleman 《GeoJournal》2007,69(1-2):93-102
Geospatial technologies and digital data have developed and disseminated rapidly in conjunction with increasing computing
efficiency and Internet availability. The ability to store and transmit large datasets has encouraged the development of national
infrastructure datasets in geospatial formats. National datasets are used by numerous agencies for analysis and modeling purposes
because these datasets are standardized and considered to be of acceptable accuracy for national scale applications. At Oak
Ridge National Laboratory a population model has been developed that incorporates national schools data as one of the model
inputs. This paper evaluates spatial and attribute inaccuracies present within two national school datasets, Tele Atlas North
America and National Center of Education Statistics (NCES).
Schools are an important component of the population model, because they are spatially dense clusters of vulnerable populations.
It is therefore essential to validate the quality of school input data. Schools were also chosen since a validated schools
dataset was produced in geospatial format for Philadelphia County; thereby enabling a comparison between a local dataset and
the national datasets.
Analyses found the national datasets are not standardized and incomplete, containing 76 to 90 percent of existing schools.
The temporal accuracy of updating annual enrollment values resulted in 89 percent inaccuracy for 2003. Spatial rectification
was required for 87 percent of NCES points, of which 58 percent of the errors were attributed to the geocoding process. Lastly,
it was found that by combining the two national datasets, the resultant dataset provided a more useful and accurate solution. 相似文献
5.
Analysis And Simulation Of Surface-Layer Winds Using Multiplicative Cascade Models With Self-Similar Probability Densities 总被引:1,自引:0,他引:1
Statistical analysis techniques based on multiplicative cascades are investigated for use with surface-layer wind data sets collected in the atmospheric boundary layer over flat farm land. The data were found to exhibit multiscaling statistics, allowing the surface-layer winds to be simulated with the use of multiplicative random cascades. The study found evidence that, for the surface-layer at least, these cascade models (andhence the methods of multifractal analysis) should be applied in separate ways to the microscale inertial range, and the mesoscale. This is at odds with the view found in the existing literature, which proposes a `universal multifractal' model to replace the widely held view that there exists separate microscale, mesoscale and synoptic scales for which the processes governing each are different. At least two separate ranges of scaling are suggested for surface-layer wind data, corresponding to the microscale inertial range and the mesoscale. For the case of the mesoscale range, a self-similar distribution of weighting factors was found for the wind speed data themselves, rather than for an intermediate (dissipation) field, as is required for themicroscale data. 相似文献
6.
This paper describes some of the results that were obtained in an experimental study of an inversion capping a convective boundary layer, during which a balloon-borne probe was flown through the actual interface at the same time as it was scanned by a high power 10-cm Doppler radar. The initial analysis has revealed several interesting features including the possible presence of small-scale Kelvin-Helmholtz billows at the crest of the hummocks of the inversion and the absence of an inertial subrange. A model is proposed for the transfer of sensible heatdownwards across the inversion. This is hypothesised as a two-stage process — sporadic thickening by the entrainment of air from above and below due to the action of the breaking billows, and a continual erosion of the lower surface by convective activity. 相似文献
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9.
When exposed to methylmercury in the laboratory, grass shrimp, Palaemonetes pugio, parasitized by the isopod Probopyrus pandalicola, accumulated lower concentrations of mercury than their unparasitized counterparts. The parasitic isopod accumulated far less mercury than the grass shrimp. When exposed to mercury in a contaminated field site, mummichogs, Fundulus heteroclitus, parasitized with the nematode Eustrongylides, similarly accumulated lower concentrations of mercury than unparasitized fish, and the parasite similarly accumulated less than the host. The lower uptake by the parasites compared to their hosts is counter to the general view of biomagnification of methylmercury, since parasites are a trophic level above their hosts. The mechanism whereby parasitized animals accumulate less toxicant than unparasitized ones is unknown, but may be partially due to lower metabolic rate. 相似文献
10.
Bromage B.J.J. Alexander D. Breen A. Clegg J.R. Del Zanna G. DeForest C. Dobrzycka D. Gopalswamy N. Thompson B. Browning P.K. 《Solar physics》2000,193(1-2):181-193
Coronal holes on the Sun are the source of high-speed solar wind streams that produce magnetic disturbances at the Earth. A series of multi-wavelength, multi-instrument observations obtained during the 1996 Whole Sun Month campaign examined a large coronal hole in greater detail than ever before. It appeared on the Sun in August, and extended from the north pole to a large active region in the southern hemisphere. Its physical and magnetic structure and subsequent evolution are described. 相似文献