Kerogen model breakdown: Comments to Lerche (1991) and Liu and Lerche (1990)     

Soren B. Nielsen  Alan K. Burnham 《Mathematical Geology》1993,25(1):81-89

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The geography of pastoral mobility: A spatio-temporal analysis of GPS data from Sahelian Senegal     

Hanne Kirstine Adriansen  Thomas Theis Nielsen 《GeoJournal》2005,64(3):177-188

The aim of this paper is to show the contribution of geography to the study of pastoral mobility. While pastoralists of Ferlo, Senegal, have become semi-sedentary, little is known about the mobility of their livestock. In this paper, pastoral mobility is analysed using GPS measurements of cattle movements made by a pastoralist from 1997 to 2000. Based on data from 3 years, a quantification of the extent of movements and mappings of the patterns are made. The results show that cattle walk about 5000 km on an annual basis, and while a great deal of the mobility can be characterised as daily circular movements between the camp and watering points, occasional transhumance is still used to make the most of variable resources.  相似文献   

Simulating galaxy clusters – II. Global star formation histories and the galaxy populations     

Alessio D. Romeo  Laura Portinari  Jesper Sommer-Larsen 《Monthly notices of the Royal Astronomical Society》2005,361(3):983-996

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Long wavelength ground surface temperature history from continuous temperature logs in the Transylvanian Basin     

Delia Zemira erban  Sren B. Nielsen  Cri an Demetrescu 《Global and Planetary Change》2001,29(3-4)

Continuous temperature logs to depths between 750 and 1400 m in the Transylvanian Basin, Romania, in many cases show temperature gradient variations with depth which cannot be explained by depth variations in thermal conductivity, topography and ground water flow. The only possible responsible agent seems to be past surface temperature variations. The temperature logs from nine boreholes have been interpreted individually and jointly by least squares inverse modelling with the surface temperature history and background heat flux as unknown parameters. All the temperature profiles are consistent with a temperature rise at the end of the last glaciation. The effects of borehole depth, of a wrong choice of thermal conductivity, and the level of uncorrelated random noise were examined using synthetic examples.  相似文献   

Rigid‐plastic seismic design of reinforced concrete structures     

J. L. Domingues Costa  R. Bento  Vsevolod Levtchitch  M. P. Nielsen 《地震工程与结构动力学》2007,36(1):55-76

In this paper a new seismic design procedure for Reinforced Concrete (R/C) structures is proposed—the Rigid‐Plastic Seismic Design (RPSD) method. This is a design procedure based on Non‐Linear Time‐ History Analysis (NLTHA) for systems expected to perform in the non‐linear range during a lifetime earthquake event. The theoretical background is the Theory of Plasticity (Rigid‐Plastic Structures). Firstly, a collapse mechanism is chosen and the corresponding stress field is made safe outside the regions where plastic behaviour takes place. It is shown that this allows the determination of the required structural strength with respect to a pre‐defined performance parameter using a rigid‐plastic response spectrum, which is characteristic of the ground motion alone. The maximum strength demand at any point is solely dependent on the intensity of the ground motion, which facilitates the task of distributing required strength throughout the structure. Any artificial considerations intended to adjust results according to empirical observations are avoided, which, from a conceptual point of view, is considered to be an advantage over other simplified design procedures for seismic design. The procedure is formulated using a step‐by‐step format followed by a design example of a 4‐storey‐R/C‐plane‐frame. Results are compared with refined NLTHA and found to be extremely encouraging. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Tracer Tests and Image Analysis of Biological Clogging in a Two-Dimensional Sandbox Experiment   总被引：1，自引：0，他引：1  

Jesper Kildsgaard  Peter Engesgaard 《Ground Water Monitoring & Remediation》2002,22(2):60-67

A two-dimensional flow experiment on biological clogging was carried out by biostimulating a sandbox packed with sand inoculated with bacteria. Biostimulation consisted of continuously injecting nutrients (acetate and nitrate). Clogging was visualized by frequently carrying out colored tracer experiments using Brilliant Blue. The tracer experiments were recorded with a digital camera and converted to concentration maps using an image-analysis method that revealed in detail the complex spreading pattern surrounding clogged areas. Clogging resulted in a finger-like spreading of the tracer around the main clogged area. Fingers were asymmetric and their dominant direction changed over time. Although the flow field was complex around the main clogged area, the effect on the bulk hydraulic conductivity at the scale of the sandbox was very small.  相似文献   

Converted P-waves Originating at the Continental Margin between the Iceland-Faeroe Ridge and the Faeroe Block     

M. H. P. Bott  P. H. Nielsen  J. Sunderland † 《Geophysical Journal International》1976,44(1):229-238

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Prior exposure to Cu contamination influences the outcome of toxicological testing of Fucus serratus embryos     

Nielsen HD  Burridge TR  Brownlee C  Brown MT 《Marine pollution bulletin》2005,50(12):1675-1680

Brown seaweeds are often employed in single species toxicity testing to study the association between the pollutant and the biota in contaminated marine habitats. We have used Fucus serratus (Phaeophyta) from one Cu resistant and one non-resistant population to evaluate the effect of prior exposure to metal pollution on toxicological endpoints. Analysis of comparative toxicity was conducted for embryo rhizoid elongation and adult relative growth rate (RGR). Algae that had previously been exposed to Cu expressed consistently lower levels of sensitivity to Cu than those that had no history of exposure to the pollutant. For both non-resistant and resistant populations rhizoid length was a more sensitive endpoint than adult RGR. While early life history stages of brown algae are generally regarded as being pollution-sensitive and inhibition of spore and embryo rhizoid elongation is frequently used as endpoints in bioassays, the test results may be affected by prior exposure of the parent algae to the pollutant. We conclude that the effect of prior exposure should be considered when comparing endpoints between studies and when selecting material for future testing.  相似文献   

Supervised Mineral Classification with Semiautomatic Training and Validation Set Generation in Scanning Electron Microscope Energy Dispersive Spectroscopy Images of Thin Sections     

Harald Flesche  Allan Aasbjerg Nielsen  Rasmus Larsen 《Mathematical Geology》2000,32(3):337-366

This paper addresses the problem of classifying minerals common in siliciclastic and carbonate rocks. Twelve chemical elements are mapped from thin sections by energy dispersive spectroscopy in a scanning electron microscope (SEM). Extensions to traditional multivariate statistical methods are applied to perform the classification. First, training and validation sets are grown from one or a few seed points by a method that ensures spatial and spectral closeness of observations. Spectral closeness is obtained by excluding observations that have high Mahalanobis distances to the training class mean. Spatial closeness is obtained by requesting connectivity. Second, class consistency is controlled by forcing each class into 5–10 subclasses and checking the separability of these subclasses by means of canonical discriminant analysis. Third, class separability is checked by means of the Jeffreys–Matusita distance and the posterior probability of a class mean being classified as another class. Fourth, the actual classification is carried out based on four supervised classifiers all assuming multinormal distributions: simple quadratic, a contextual quadratic, and two hierarchical quadratic classifiers. Overall weighted misclassification rates for all quadratic classifiers are very low for both the training (0.25–0.33%) and validation sets (0.65–1.13%). Finally, the number of rejected observations in routine runs is checked to control the performance of the SEM image acquisition and the classification. Although the contextual classifier performs marginally best on the validation set, the simple quadratic classifier is chosen in routine classifications because of the lower processing time required. The method is presently used as a routine petrographical analysis method at Norsk Hydro Research Centre. The data can be approximated by a Poisson distribution. Accordingly, the square root of the data has constant variance and a linear classifier can be used. Near orthogonal input data, enable the use of a minimum distance classifier. Results from both linear and quadratic minimum distance classifications are described briefly.  相似文献   

Integrated gravity and wide-angle seismic inversion fortwo-dimensional crustal modelling     

Lars Nielsen  & Bo Holm Jacobsen 《Geophysical Journal International》2000,140(1):222-232

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