Dynamic response of debris flows impacting curved joint check dams     

《国际泥沙研究》2022,37(5):589-600

The dynamic impact force of debris flow on dams with a curved upstream face curved was investigated using laboratory experiments and a theoretical approach. Equations describing the impact force and maximum run-up height were derived. The experiments and theoretical considerations reveal that the impact force and maximum run-up height are mainly controlled by the Froude number (Fr) reduced by the cosine of the channel slope angle (cosα). Both the impact force and the maximum run-up height have a quadratic relation with the modified Froude number (Fr/(cosα)^0.5). The experimental data and the results of the theoretical approach are in good agreement, indicating that the theoretical approach can be used in practical applications. It is concluded that the comparison between the curved-joint dam and the more conventional sharp-joint dam shows no differences in the maximum impact force and run-up height for the same modified Froude number. With the sharp-joint dam, the peak values of the impact force are reached more quickly than with the curved-joint dam.  相似文献   

独立分量分析改进的图像去噪方法     

杨信能  朱宝山 《测绘科学》2015,40(3):132-134

针对传统去噪算法在复杂噪声污染图像处理中能力较弱的问题,该文基于信号高阶统计量的独立分量分析,通过其自适应变换,分离出源信号中的统计独立的分量,在分析对比传统图像去噪方法的基础上,讨论了独立分量分析的基本模型及原理;提出了一种结合中值滤波与wiener滤波的最大似然估计的图像去噪改进方法。仿真实验表明改进的独立分量分析去噪方法具有较大的优越性。  相似文献   

Linking pesticides and human health: A geographic information system (GIS) and Landsat remote sensing method to estimate agricultural pesticide exposure     

《Applied geography (Sevenoaks, England)》2015

Accurate pesticide exposure estimation is integral to epidemiologic studies elucidating the role of pesticides in human health. Humans can be exposed to pesticides via residential proximity to agricultural pesticide applications (drift). We present an improved geographic information system (GIS) and remote sensing method, the Landsat method, to estimate agricultural pesticide exposure through matching pesticide applications to crops classified from temporally concurrent Landsat satellite remote sensing images in California. The image classification method utilizes Normalized Difference Vegetation Index (NDVI) values in a combined maximum likelihood classification and per-field (using segments) approach. Pesticide exposure is estimated according to pesticide-treated crop fields intersecting 500 m buffers around geocoded locations (e.g., residences) in a GIS. Study results demonstrate that the Landsat method can improve GIS-based pesticide exposure estimation by matching more pesticide applications to crops (especially temporary crops) classified using temporally concurrent Landsat images compared to the standard method that relies on infrequently updated land use survey (LUS) crop data. The Landsat method can be used in epidemiologic studies to reconstruct past individual-level exposure to specific pesticides according to where individuals are located.  相似文献   

Last Glacial Maximum Sea Surface Temperatures: A Model-Data Comparison          下载免费PDF全文

WANG Tao  LIU Yi  HUANG Wei 《大气和海洋科学快报》2013,6(5):233-239

In this study,the authors investigated changes in Last Glacial Maximum(LGM)sea surface temperature(SST)simulated by the Paleoclimate Modelling Intercomparison Project(PMIP)multimodels and reconstructed by the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface(MARGO)project,focusing on model-data comparison.The results showed that the PMIP models produced greater ocean cooling in the North Pacific and Tropical Ocean than the MARGO,particularly in the northwestern Pacific,where the modeldata mismatch was larger.All the models failed to capture the anomalous east-west SST gradient in the North Atlantic.In addition,large discrepancies among the models were observed in the mid-latitude ocean,particularly with models in the second phase of the PMIP.Although these models showed better agreement with the MARGO,the latest models in the third phase of the PMIP did not show substantial progresses in simulating LGM ocean surface conditions.That is,improvements in the modeling community are still needed to describe SST for a better understanding of climate during the LGM.  相似文献   

喀什地区1961—2010年最大冻土深度变化     

阿布都克日木·阿巴司 《沙漠与绿洲气象(新疆气象)》2013,7(3):25-29

利用1961～2010年喀什地区所属喀什市、莎车县、巴楚县、塔什库尔干县等4个代表性站50a的年最大冻土深度、冬季平均气温、极端最低气温、极端最低地温等资料,采用气候趋势系数和气候倾向率方法,对1961年以来喀什地区最大冻土深度变化进行了分析。结果表明,喀什地区平原多年平均最大冻土深度为48.1 cm,年际最大值与最小值深度差为82cm,随年际变化总体呈明显的减小趋势,其变化倾向率为-3.8cm/10a,年代际变化呈阶梯状逐渐减小,冻土深度减小主要受冬季平均气温升高的影响,气温每升高1℃,冻土深度减小7.75 cm;山区多年平均最大冻土深度为148.8cm,年际最大值与最小值深度差为88cm,随年际变化总体呈明显的减小趋势,其变化倾向率为-2.5cm/10a。  相似文献   

The Last Glacial Maximum in the North Sea Basin: micromorphological evidence of extensive glaciation     

S. J. Carr  R. Holmes  J. J. M. van der Meer  J. Rose 《第四纪科学杂志》2006,21(2):131-153

Despite a long history of investigation, critical issues regarding the last glacial cycle in northwest Europe remain unresolved. One of these refers to the extent, timing and dynamics of Late Devensian/Weichselian glaciation of the North Sea Basin, and whether the British and Scandinavian ice sheets were confluent at any time during this period. This has been the result of the lack of the detailed sedimentological data required to reconstruct processes and environment of sediments recovered through coring. This study presents the results of seismic, sedimentological and micromorphological evidence used to reconstruct the depositional processes of regionally extensive seismic units across the North Sea Basin. Thin section micromorphology is used here to provide an effective means of discriminating between subglacial and glacimarine sediments from cored samples and deriving process‐based interpretations from sediment cores. On the basis of micromorphology, critical formations from the basin have been reinterpreted, with consequent stratigraphic implications. Within the current stratigraphic understanding of the North Sea Basin, a complex reconstruction is suggested, with a minimum of three major glacial episodes inferred. On at least two occasions during the Weichselian/Devensian, the British and Scandinavian ice sheets were confluent in the central North Sea. Whilst micromorphology can provide much greater confidence in the interpretation of Late Quaternary offshore stratigraphic sequences, it is noted that a much better geochronology is required to resolve key stratigraphic issues between the onshore and offshore stratigraphic records. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Fossil hyrax dung and evidence of Late Pleistocene and Holocene vegetation types in the Namib Desert     

Louis Scott  Eugene Marais  George A. Brook 《第四纪科学杂志》2004,19(8):829-832

Pollen was derived from fossil dung of herbivorous hyraxes, deposited in a rock shelter on the highest mountain in Namibia, Dâures or Brandberg, situated on the Namib Desert margin. Radiocarbon dating ranging in age between modern times and 30 000 yr BP showed it represents the first empirical pollen evidence of continental palaeovegetation during the Late Pleistocene along the western escarpment of southern Africa. The initial results indicate Last Glacial Maximum vegetation differed totally from the current pattern as vegetation types were dominated by small Asteraceae shrubs, in contrast to those of the Holocene and modern times which show more succulents, grass and woody elements (arboreal pollen). The results suggest that Cape floral communities did not reach into the tropics along the western escarpment of Africa, despite such pollen types occurring in marine cores. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Polynomial expansions in likelihoods for spatial data: A case study     

A. J. Watkins  P. Heatley 《Mathematical Geology》1996,28(8):987-999

This paper illustrates the computational benefits of polynomial representations for quantities in the likelihood function for the spatial linear model based on the power covariance scheme. These benefits include a comprehensive study of likelihoods and maximum likelihood estimators for data. For simplicity, we focus on a relatively simple covariance scheme and data observed at equal intervals along a transect; we briefly indicate how generalizations to more complicated covariance functions and higher dimensions will operate.  相似文献   

Mixture models and atypical values     

N. A. Campbell 《Mathematical Geology》1984,16(5):465-477

The resolution of a mixture of two or more populations into its component distributions may be markedly influenced by one or a few atypical values. The maximum likelihood solution effectively assigns (part of) each observation to one or another of the components via the posterior probabilities, even though the observation may be widely discrepant from all components. This paper presents a modification of the mixture problem, in which the typicality of each observation is considered, as well as the posterior probabilities, with the contribution of atypical observations being downweighted. The extension to the multivariate case is discussed.  相似文献   

A note on the calculation of covariance and resolution     

Robert L. Nowack  William J. Lutter 《Geophysical Journal International》1988,95(1):205-207

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