Dust supply from river floodplains: the case of the lower Huang He (Yellow River) recorded in a loess–palaeosol sequence from the Mangshan Plateau     

Maarten A. Prins  Hongbo Zheng  Kay Beets  Simon Troelstra  Patrick Bacon  Ilse Kamerling  Wouter Wester  Martin Konert  Xiangtong Huang  Wang Ke  Jef Vandenberghe 《第四纪科学杂志》2009,24(1):75-84

The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Rapid climatic changes recorded in loess successions     

J. Vandenberghe  G. Nugteren 《Global and Planetary Change》2001,28(1-4)

Detailed grain-size analyses, both in China and western Europe, indicate the occurrence of short climatic cycles during loess deposition of the last glacial. Cold episodes coincided with enhanced deposition of relatively coarse loess and alternated with relatively warmer episodes with decreased deposition of finer loess and soil formation. In Europe, these oscillations may coincide with alternations of permafrost development and degradation. The short-term climatic events in the loess sections are similar to the Dansgaard–Oeschger events in ice-core records.  相似文献   

Palaeotemperature reconstructions of the European permafrost zone during marine oxygen isotope Stage 3 compared with climate model results     

Ko van Huissteden  Jef Vandenberghe  David Pollard 《第四纪科学杂志》2003,18(5):453-464

A palaeotemperature reconstruction based on periglacial phenomena in Europe north of approximately 51 °N, is compared with high‐resolution regional climate model simulations of the marine oxygen isotope Stage 3 (Stage 3) palaeoclimate. The experiments represent Stage 3 warm (interstadial), Stage 3 cold (stadial) and Last Glacial Maximum climatic conditions. The palaeotemperature reconstruction deviates considerably for the Stage 3 cold climate experiments, with mismatches up to 11 °C for the mean annual air temperature and up to 15 °C for the winter temperature. However, in this reconstruction various factors linking climate and permafrost have not been taken into account. In particular a relatively thin snow cover and high climatic variability of the glacial climate could have influenced temperature limits for ice‐wedge growth. Based on modelling the 0 °C mean annual ground temperature proves to be an appropriate upper temperature limit. Using this limit, mismatches with the Stage 3 cold climate experiments have been reduced but still remain. We therefore assume that the Stage 3 ice wedges were generated during short (decadal time‐scale) intervals of extreme cold climate, below the mean temperatures indicated by the Stage 3 cold climate model simulations. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Al hematites prepared by homogeneous precipitation of oxinates: material characterization and determination of the Morin transition     

G. M. da Costa  E. Van San  E. De Grave  R. E. Vandenberghe  V. Barrón  L. Datas 《Physics and Chemistry of Minerals》2002,29(2):122-131

A novel method for synthesis of aluminium hematites, based upon the homogeneous precipitation of Fe and Al oxinates in various proportions, is presented. The precursor precipitates are heated in air at 700?°C. X-ray diffraction, thermal analyses, BET, FTIR, optical reflection analysis, TEM and Mössbauer spectroscopy at room temperature and 80?K of the resulting products indicate that single-phase hematites are formed with structural Al substitution of up to 10 at%. Interestingly, the particle size (>100?nm) is not substantially reduced by the Al content. Although it remains difficult to obtain a homogeneously distributed Al substitution in the final hematite, this processing line offers a unique opportunity to separate the effects of grain size and Al substitution on the Morin transition temperature (T _M) of Al hematite. From the comparison between the present hematites and a series of Al-substituted hematites with lepidocrocite as precursor, it could be shown that the effect on T _M, associated with a change of a factor 10 in grain size, is about 1/3 of the effect caused by a change of 10 in the degree of substitution. Finally, it is suggested that proper thermal treatments under different conditions of the same precursors are likely to produce spinel phases.  相似文献   

Spectral-element simulations of global seismic wave propagation—II. Three-dimensional models, oceans, rotation and self-gravitation     

Dimitri Komatitsch  Jeroen Tromp 《Geophysical Journal International》2002,150(1):303-318

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Tensorial formulation of the wave equation for modelling curved interfaces   总被引：1，自引：0，他引：1  

Dimitri Komatitsch  Fabien Coutel  Peter Mora 《Geophysical Journal International》1996,127(1):156-168

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Risk Assessment of Soil Compaction in the Walloon Region in Belgium   总被引：1，自引：0，他引：1  

Dimitri D’Or  Marie-France Destain 《Mathematical Geosciences》2016,48(1):89-103

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Geomorphological evolution of a Lowland valley system during the Weichselian     

J. Van Huissteden  L. Van Der Valk  J. Vandenberghe 《地球表面变化过程与地形》1986,11(2):207-216

Weichselian geomorphological and fluvial evolution has been recorded in the valley fill of the Reusel, a small tributary of the lower Maas river. It has been studied by means of borehole sections. A first deep incision into the substratum occurred during the Early Weichselian-Lower Pleniglacial. This was followed by aggradation, at first by a braided river, at a later date by a meandering river, dating respectively from the Lower and Middle Pleniglacial. The Upper Pleniglacial aggradation again points to a braided river system. The end of the Pleniglacial is characterized by aeolian infilling of the valley and decreasing carrying capacity of the river.  相似文献   

Uniform half-plane elastodynamic problems by an approximate boundary element method     

Dionyssia-Pinelopi N. Kontoni  Dimitri E. Beskos 《Soil Dynamics and Earthquake Engineering》1987,6(4):227-238

In this paper the applicability of an approximate Boundary Element Method to uniform half-plane elastodynamic problems is investigated. This method employs the concept of images to construct approximate fundamental solutions for the half-plane and does not require any half-plane surface discretization. The method is formulated in the frequency domain for the case of harmonic disturbances or the Laplace transform domain for the case of transient disturbances. In the latter case a numerical inversion of the transformed solution is necessary to obtain the time domain response. The proposed method can be used as an alternative to boundary element methods that either utilize the infinite plane fundamental solution and thus require a half-plane surface discretization, or employ the exact half-plane fundamental solution, which even though leads to no surface discretization, is of a very lengthy and complicated form. Two characteristics numerical examples are used to illustrate the proposed method and study its advantages and disadvantages.  相似文献   

Contribution au probleme de la compensation des reseaux de triangulation     

Dimitri G. Vlachos 《Journal of Geodesy》1970,44(3):213-223

Résumé Dans cette étude on expose une adaptation de la méthode des directions —pour la compensation d’un réseau de triangulation—aux possibilités de l’ordinateur électronique. On présente les formules par lesquelles on calcule les coefficients des inconnues dans les équations de condition (équations aux angles et équations aux c?tés) et on dresse leur matrice. Ensuite on traite de la formation de la matrice des coefficients des équations normales et son inversion, qui fournit les quantités corrélatives de Lagrange. Enfin, après avoir déterminé les corrections à apporter aux directions observées, on calcule l’erreur moyenne quadratique d’une observation isolée et l’erreur moyenne de chacune des directions compensées.

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Summary In this study, an adaptation to the computers’ possibilities, regarding the method of directions, is disclosed in order to realise the adjustment of triangulation nets. The computing formulae of the coefficients of the unknown quantities in the condition equations and the creation of their matrix are given herebelow. The treatment leading towards the construction of the matrix of normal equations and its inversion, that furnishes Lagrange’s quantities, follows. After the computation of the corrections applied on the observed directions, the mean error of a single observation and the mean error of every adjusted direction are determined. The study is executed in such a way that it can be included in only one programme for automatic computation.

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