Robust Resampling Confidence Intervals for Empirical Variograms   总被引：1，自引：0，他引：1  

Robert Graham Clark  Samuel Allingham 《Mathematical Geosciences》2011,43(2):243-259

The variogram function is an important measure of the spatial dependencies of a geostatistical or other spatial dataset. It plays a central role in kriging, designing spatial studies, and in understanding the spatial properties of geological and environmental phenomena. It is therefore important to understand the variability attached to estimates of the variogram. Existing methods for constructing confidence intervals around the empirical variogram either rely on strong assumptions, such as normality or known variogram function, or are based on resampling blocks and subject to edge effect biases. This paper proposes two new procedures for addressing these concerns: a quasi-block-bootstrap and a quasi-block-jackknife. The new methods are based on transforming the data to decorrelate it based on a fitted variogram model, resampling blocks from the decorrelated data, and then recorrelating. The coverage properties of the new confidence intervals are compared by simulation to a number of existing resampling-based intervals. The proposed quasi-block-jackknife confidence interval is found to have the best properties of all of the methods considered across a range of scenarios, including normally and lognormally distributed data and misspecification of the variogram function used to decorrelate the data.  相似文献   

The strength of biogenic sand reefs: Visco-elastic behaviour of cement secreted by the tube building polychaete Sabellaria alveolata, Linnaeus, 1767     

Jean-Benoît Le Cam  Jérôme Fournier  Samuel Etienne  Jérôme Couden 《Estuarine, Coastal and Shelf Science》2011

Mechanical properties of the biomineralised cement from tube-building marine worms are poorly known. Secreted from an organ connected to the polychaetes specialised glands, the cement glues sand grains and calcareous shell fragments of a given size and, on a larger scale, ensures the resistance of the reef to waves. In this study, three kinds of mechanical tests were performed with worm tubes to establish the nature of the cement behaviour. Results obtained show that cement behaves like a visco-elastic material. This property allows the tubes to dissipate the mechanical energy from the waves to which they are subject and to reduce the mechanical stress transmitted inside the tubes to the polychaetes. Comparison of “fresh” and “dry” cements highlights that the visco-elastic behaviour of the cement is maintained after five years. The viscosity of the cement is therefore not related to moisture but to its chemical composition. More generally, these results offer a better understanding of the role of cement on worm reefs strength and their persistence in the geological record.  相似文献   

Fine-scale population structure in a deep-sea teleost (orange roughy, Hoplostethus atlanticus)     

Jens Carlsson  Samuel Shephard  James CoughlanClive N. Trueman  Emer RoganTom F. Cross 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(6):627-636

Microsatellite and otolith chemistry variability were analysed to assess fine scale genetic structure in the deep-sea teleost orange roughy (Hoplostethus atlanticus). The Porcupine Bank located on the continental shelf west of Ireland, comprises a complex system of mounds and flat areas that are broken up by canyons. Orange roughy form spawning aggregations on mounds and flat areas, and were heavily fished until the resource was depleted. By analysing adults in spawning condition and juvenile orange roughy from six mounds and one flat area, shallow but significant genetic population structure was evident (F_ST=0.0031, D_est across loci=0.0306 and G-test). Most of the structure was accounted for by inclusion of a sample from the flats (six of ten significant pairwise F_ST estimates and G-tests, and five of the highest D_est estimates included the flat sample). While the flat sample contributed most to the genetic structure, there was still significant (albeit weaker) structure among mound samples. The observed structure was supported by otolith analyses. Fish caught as late juveniles in either the flat or mound areas showed consistent differences in chemistry at the otolith core throughout the initial 10 years of growth, which could indicate site fidelity. We hypothesise that seafloor topographic structures (mounds and flats) may provide discrete spawning areas for orange roughy and that the limited gene flow between these spawning areas is insufficient to counteract genetic drift.  相似文献   

Theoretical mean wave resistance of precursor soliton generation of single-layer flow     

徐肇廷  史峰岩  楼顺里  Samuel Shan-pu SHEN 《中国海洋湖沼学报》1996,14(4):330-336

Theoretical mean wave resistance and regional division of the energy of single-layer flow over topogra-phy is studied at the near-resonant region in the weakly nonlinear, long wave limit. The theoretical meanwave resistance is determined in terms of the 1st and 2nd conservation laws of the fKdV equation. It isproved by the asymptotic mean method that the theoretical mean wave resistance depends only on the intensityand moving velocity of the topography. The theoretical results of this paper are in good agreement withnumerical calculations. Comparisons between the theoretical and numerical results showed that the theoryof the present paper holds for any small compact topography.  相似文献   

A Compilation of Silicon and Thirty One Trace Elements Measured in the Natural River Water Reference Material SLRS-4 (NRC-CNRC)   总被引：1，自引：0，他引：1  

Delphine Yeghicheyan  Jean Carignan  Michel Valladon  Martine Bouhnik Le  Coz  Florence Le Cornec  Maryse Castrec-Rouelle  Michel Robert  Luc Aquilina  Emmanuel Aubry  Carine Churlaud  Aline Dia  Samuel Deberdt  Bernard Dupré  Rémi Freydier  Gérard Gruau  Odile Hénin  Anne-Marie de  Kersabiec  Joël Macé  Luc Marin  Nicole Morin  Patrice Petitjean  Elodie Serrat 《Geostandards and Geoanalytical Research》2001,25(2-3):465-474

The natural river water certified reference material SLRS-4 (NRC-CNRC, National Research Council-Conseil National de Recherches Canada) has been routinely analysed for major and trace elements by six French laboratories. Most measurements were made using inductively coupled plasma-mass spectrometry. For silicon and thirty one trace elements (rare earth elements, Ag, B, Br, Cs, Ga, Ge, Li, P, Pd, Rb, Se, Th, Ti, Tl, W, Y and Zr), no certified values are assigned by NRC-CNRC. We propose some compilation values and related uncertainties according to the results obtained by the different laboratories.  相似文献   

Geomorphic application of the hausdorff-besicovich dimension     

Samuel I. Outcalt  Mark A. Melton 《地球表面变化过程与地形》1992,17(8):775-787

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The force-restore method revisited     

Samuel Y. K. Yee 《Boundary-Layer Meteorology》1988,43(1-2):85-90

The so-called ‘force-restore method’ has been used with considerable success in numerical weather prediction models to simulate diurnal variations of ground temperature. This note demonstrates that the force-restore equation is no more nor less than an approximation to the surface-energy-balance equation. The applicability of the method to the case of multi-component heating functions and to the case in which the soil is covered by a litter layer is discussed.  相似文献   

A 1600-year record of human impacts on a floodplain lake in the Mississippi River Valley     

Richard B. Brugam  Samuel E. Munoz 《Journal of Paleolimnology》2018,60(3):445-460

In North America, land use practices of the last two centuries have strongly influenced aquatic communities and freshwater quality, but the impacts of prehistoric land use on freshwater resources remain poorly documented. Here we investigate the influence of prehistoric and historical land use on Horseshoe Lake, Illinois, USA, an oxbow lake in a floodplain of the Mississippi River that is adjacent to Cahokia, the largest prehistoric indigenous population center north of Mexico. Diatom assemblages from Horseshoe Lake’s sedimentary record track shifts in aquatic environmental conditions over the last ca. 1600 years. During the period of prehistoric population growth and agricultural intensification associated with Cahokia’s emergence (ca. 600–1200 CE), the relative abundance of Aulacoseira granulata—a planktonic diatom associated with shallow eutrophic lakes—increased. Following the abandonment of Cahokia in the 14th century CE, the diatom flora of the lake shifted from planktonic Aulacoseira taxa to the epiphytic taxa Cocconeis and Gomphonema. This shift in diatom assemblages is consistent with a reduction of nutrient inputs to the lake and/or reduced fishing pressure as prehistoric populations abandoned the area. Following the intensification of historic settlement after 1800 CE, diatom assemblages shift to epipelic species of small Staurosira and Fragilaria, indicating a reduction in aquatic macrophytes and increased turbidity. Our results document prehistoric indigenous impacts on a freshwater system beginning nearly 1000 years before European colonization of the Americas and demonstrate the antiquity of human impacts on freshwater resources in North America.  相似文献   

Future evolution of extreme precipitation in the Mediterranean     

Yves Tramblay  Samuel Somot 《Climatic change》2018,151(2):289-302

Mediterranean basins can be impacted by severe floods caused by extreme rainfall, and there is a growing awareness about the possible increase in these heavy rainfall events due to climate change. In this study, the climate change impacts on extreme daily precipitation in 102 catchments covering the whole Mediterranean basin are investigated using nonstationary extreme value model applied to annual maximum precipitation in an ensemble of high-resolution regional climate model (RCM) simulations from the Euro-CORDEX experiment. Results indicate contrasted trends, with significant increasing trends in Northern catchments and conversely decreasing trends in Southern catchments. For most cases, the time of signal emergence for these trends is before the year 2000. The same spatial pattern is obtained under the two climate scenarios considered (RCP4.5 and RCP8.5) and in most RCM simulations, suggesting a robust climate change signal. The strongest multi-model agreement concerns the positive trends, which can exceed +?20% by the end of the twenty-first century in some simulations, impacting South France, North Italy, and the Balkans. For these areas, society-relevant strong impacts of such Mediterranean extreme precipitation changes could be expected in particular concerning flood-related damages.  相似文献   

Supra-subduction and abyssal mantle peridotites of the Coast Range ophiolite,California   总被引：6，自引：0，他引：6  

Sung Hi Choi  John W. Shervais  Samuel B. Mukasa 《Contributions to Mineralogy and Petrology》2008,156(5):551-576

The Coast Range ophiolite (CRO) of California is one of the most extensive tracts of oceanic crust preserved in the North American Cordillera, but its origin has long remained controversial. We present here new data on mineral compositions in mantle peridotites that underlie crustal sections of the ophiolite, and show that these are dominantly refractory harzburgites related to high apparent melting in a supra-subduction zone (SSZ) setting. Abyssal peridotite (characterized by high-Al spinels and relatively high Ti, Na, Nd, Sm, Lu, and Hf in pyroxene) occurs at one location where it is associated with SSZ mantle peridotite and volcanic rocks with both oceanic and arc-like geochemistry. SSZ mantle peridotites (characterized by intermediate-Cr/Al or high-Cr spinels, and by extremely low Ti, Na, Nd, Sm, Lu, and Hf in pyroxenes) are associated with crustal sections containing arc-related volcanic rocks, including boninites. This convergence between conclusions based on crustal lithologies and their underlying mantle sections confirms previous proposals that link the CRO to SSZ processes, and seriously undermines hypotheses that invoke formation of the ophiolite at a mid-ocean ridge spreading center.  相似文献