A model for presentation of seismic pore water pressures   总被引：3，自引：0，他引：3  

Tomislav Iv&#x;i&#x; 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):191-199

A model for presentation of pore water pressures induced in sand samples during cyclic undrained testing is described. The proposed model belongs to a class of so-called ‘damage parameter models’, which correlate the pore pressure rise with a parameter based on an accumulated variable during testing. The concept of threshold strain is also incorporated in the model. The model has been verified on several series of published cyclic test data. Its parameters lie in a narrow band for a wide range of sand properties. The empirical functions that represent the common shape of individual curves for interpreted pore pressure data are also suggested. The proposed procedure has been adapted for presentation of other cyclic soil tests, and examples of interpretation of cyclic stress-controlled as well as cyclic drained tests are included.  相似文献   

气候变化对中国农业温度阈值影响研究及其不确定性分析   总被引：10，自引：0，他引：10  

熊伟  居辉  许吟隆  林而达 《地球科学进展》2006,21(1):70-76

气候变化影响的温度阈值已经成为国际谈判的焦点问题。利用区域气候模式和作物模型相连接的方法，在50 km×50 km的网格尺度上模拟了IPCC (International Panel of Climate Change) SRES (Special Report on Emissions Scenarios) A2和B2情景下2011—2040年、2041—2070年和2071—2100年我国3种主要粮食作物（水稻、小麦和玉米）的平均单产变化情景，结合同时段的中国地区温度升高状况分析了造成我国主要粮食作物产量持续下降的升温阈值，并对阈值研究中的不确定性进行了初步分析。结果表明：如果同时考虑升温和CO2的肥效作用对作物的影响，目前预测的气温升高范围（0.9～3.9℃）中将不存在威胁我国粮食生产的温度阈值；而如果仅考虑升温对作物的影响时，全国平均温度升高2℃以后，将导致我国粮食单产水平的持续下降，威胁未来的粮食生产；气候变化适应措施如充分灌溉、播种期的调整和品种更替对阈值的确定有一定的影响，如单考虑充分灌溉可以使上述升温阈值延后到2.5℃左右，而播种期的调整和品种的更替也会对产量和产量变率造成一定的影响，进而调整温度阈值；目前研究的不确定性主要来源于情景、方法和适应措施3个方面。  相似文献   

A statistical assessment on the stochastic relationship between biomarker concentrations and environmental exposures   总被引：1，自引：1，他引：0  

C.-C.?Chen  K.-Y.?WuEmail author  M. J. W.?Chang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2004,18(6):377-385

Biological monitoring has gradually developed into a powerful tool in the identification and quantification of exposures to occupational and/or environmental hazards in environmental and occupational health studies. Aggregate individual exposure to pollutants and evidence for exploring dose-response relationship in the human bodies can be assessed through biomarker measurements. The existence of inter-individual differences among a study population, however, often hampers the relationship assessment between exposure and the biomarker. In this paper, a statistical random effects model identified from a simplified one-compartment pharmacokinetic model is applied to establish the dynamic relationship between a biomarker and its corresponding external exposure. This model avoids the complex parameter estimation problem encountered using a physiologically based pharmacokinetic (PBPK) model, and incorporates inter-individual variations often ignored in the usual regression approach. In addition, the relevant parameters for the generic kinetic process can be estimated directly. As a guideline for preliminary sampling strategy, tables of required sample sizes and the number of repeated measurements to achieve the desired statistical power and test efficiency are given. The currently established biological exposure indices (BEIs) for benzene and methyl chloroform are employed to illustrate the impact of inter- individual variations on the percentages of protection for workers exposed to the threshold limit value (TLV) of the corresponding chemical.This research was partially supported by the Environmental Protection Agency of Taiwan (Contract No. EPA-88-E102–03–003).  相似文献   

利用门限自回归建模预测广东地区2000年前后的地震强度     

刘特培 《华南地震》1998,18(3):41-45

利用自激励门限自回归建模的原理和方法,对广东地区陆地和珠江口外以及台湾海峡部分地区２０００年前后的最大地震强度进行了预测。结果表明,该区至２００１年可能发生地震的最大震级为ＭＬ５．２级,未来几年内发生Ｍ≥６．０级地震的可能性较小。  相似文献   

Lias clay slope sections and their implications for the prediction of limiting or threshold slope angles     

R. J. Chandler 《地球表面变化过程与地形》1982,7(5):427-438

  相似文献   

Profile response of a lacustrine multiple barred nearshore to a sequence of storm events     

Chris Houser  Brian Greenwood 《Geomorphology》2005,69(1-4):118-137

Profile change in a lacustrine multiple-barred nearshore was investigated over the ice-free season of 2001/2002 at Burley Beach on the southeastern shore of Lake Huron in order to identify the feedback mechanisms between the pre-existing morphology and the wave forcing and the consequence of those feedbacks to the behaviour of the nearshore environment. The characteristics of the offshore wave field were monitored using a Falmouth Scientific combined 3D-ACM wave recorder and pressure transducer. Supplemental wave data were downloaded from a 3-m discus buoy operated by the National Data Buoy Center, 75 km to the NW of the study site. The three nearshore bars were in a quasi-equilibrium state through a large part of the ice-free season, with dramatic changes occurring during relatively moderate storm events that followed much larger storms in late October. A comparison of the incident wave field with changes in the nearshore profile through canonical correlation analysis indicates that the morphology responds to the distribution of the significant, root-mean-square (rms) and average wave heights between surveys. The threshold between bar decay and onshore bar migration and growth is associated with the onset of breaking of the rms wave at the bar crest (H_rms h_cr⁻¹ ≈0.3–0.4). The threshold between onshore and offshore migration is associated with the onset of breaking of the average wave at the bar crest (H_avg h_cr⁻¹ ≈0.3–0.4), coincident with complete dissipation of the significant wave over the lakeward slope of the bar (H_s h_cr⁻¹ >0.6). Inshore wave data collected during an instrumented study at the same site revealed that the middle and inner bars remained at the threshold of onshore and offshore migration over a wide range of offshore significant wave heights (0.8 to 2.4 m) prior to the October storms. This self-organised equilibrium is a result of changes to the incident wave distribution through breaking on the outer bar. It is concluded that the prediction of bar response requires an understanding of the feedback between the bar and the local wave distribution in addition to an understanding of the feedback associated with the profile as a whole.  相似文献   

伽师强震群活动过程中喀什台地磁加卸载响应比变化特征研究     

史勇军  孙燕萍  朱燕  范素琴  巴克·买买提  热汗古·衣明克力木 《内陆地震》2002,16(1):84-88

应用地磁响应比方法 ,分析计算了喀什地磁台 1996— 1999年地磁资料 ,结果表明在伽师强震前地磁场有明显的异常 ,这为震磁信息提取和异常判断提供了依据  相似文献   

2000年前辽宁地区地震活动趋势预测     

Sun Wenfu Gu Haoding 《东北地震研究》1995,(3)

根据数理统计理论和有关文献，利用辽宁地区（３８．７°－４３°Ｎ，１１９°－１２５°Ｅ）１９７０年以来的地震资料，建立了逐年最高震级时间序列的门限自回归模型和修改的震级一频度关系。同时，对辽宁地区地震活动的时空分布特征也作了详细的研究。最后，对辽宁地区未来（到２０００年）地震活动趋势和强度作了预测。  相似文献   

用模式识别方法划分辽宁及其邻区的潜在震源区   总被引：1，自引：0，他引：1       下载免费PDF全文

蒋秀琴  王国新 《地震地质》1993,15(1):51-56

采用Cora-3修改方法和Hamming方法对辽宁及其邻区的地震地质、地球物理场和地震活动性特征进行研究,划分了6级、6.5级和7级以上潜在震源区,两种方法所得结果基本一致。经k值试验、删除对象试验和删除特征试验,均表明结果比较稳定可靠。这一成果弥补了辽宁地区这方面工作的不足,并为确定辽宁及其邻区的潜在震源区提供了依据  相似文献   

Threshold of coarse sediment transport in broad and narrow natural streams     

P. A. Carling 《地球表面变化过程与地形》1983,8(1):1-18

The threshold of coarse sediment transport has been examined in natural streambeds in an upland Pennine (U.K.) area. Threshold values of the total boundary shear stress (T₀) (for a given grain size), in a narrow natural stream (W/D < 11) are considerably higher than values of T₀ in a broad stream (W/D > 11). Efficiency in the entrainment process is related not only to the overall channel geometry, but also varies as a function of discharge in channels characterized by compound roughness. Empirical curves relating T₀ and a mean grain size (d ₅) are presented, but are limited in application to streams of similar physical and hydraulic characteristics as the ones examined in this investigation. Considerable divergence is noted between these empirical functions and a summary empirical function for general application obtained from a published source. The reasons for this divergence are discussed. The influence of grain shape was found not to be important in the initiation of motion criterion. This conclusion may reflect the limited range of natural grain shapes in the study streams, but might reasonably apply to other field investigations of similar streams. Modifications of the Shields' and Yalin diagrams are suggested for practical applications in shallow streams with poorly-graded bed material. The Shields' parameter may be regarded as an inverse function of the relative protrusion of individual grains in the shallow flow depth (d ₅/D). The increased importance of augmented drag forces, in the entrainment process in shallow flows, is suggested as the physical explanation for the reduced values of the Shields' parameter. However, the relationships presented should not be applied to laboratory experiments concerned with well-graded sediments (therefore beds with little deviation in level), in which the Shields' parameter may be regarded as constant at high Reynolds' grain numbers. Consistent estimated field values of ?, a threshold sediment transport parameter, might be used to compare field data to threshold values derived from statistical arguments and laboratory experiments reported in the literature.  相似文献