IAG Newsletter     

Ole Baltazar Andersen 《Journal of Geodesy》2002,76(4):238-245

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IAG Newsletter     

O. B. Andersen 《Journal of Geodesy》2000,74(3-4):376-380

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Terrestrial carbon-isotope records from coastal deposits (Algarve, Portugal): a tool for chemostratigraphic correlation on an intrabasinal and global scale     

Ulrich Heimhofer  Peter A. Hochuli  Stefan Burla  Nils Andersen  Helmut Weissert 《地学学报》2003,15(1):8-13

ABSTRACT The carbon-isotope signature of terrestrial organic matter (OM) offers a valuable tool to develop stratigraphic correlations for near-shore deposits. A mid-Cretaceous coastal succession of the western Algarve Basin, Portugal, displays a marked negative δ¹³C excursion ranging from − 21.2‰ to − 27.8‰ in the Early Aptian followed by two shifts towards higher values (up to − 19.3‰) during the Early and Late Aptian, respectively. The dominance of cuticle and leaf debris in the bulk OM fraction is confirmed by optical studies, Rock-Eval pyrolysis and by comparison with the δ¹³C signature of four different types of fossilized land-plant particles. Correlation of two terrestrial δ¹³C_bulk OM records from different study sites leads to a significant enhancement of the intrabasinal stratigraphic correlation within the Algarve Basin. Three prominent excursions in the Portuguese records can be correlated with existing δ¹³C curves from pelagic and terrestrial environments. The general carbon-isotope pattern is superimposed by small-scale fluctuations which can be explained by compositional variations within the OM.  相似文献   

MAX, a Laue diffraction lens for nuclear astrophysics     

N. Barrière  P. von Ballmoos  H. Halloin  N. Abrosimov  J. M. Alvarez  K. Andersen  P. Bastie  S. Boggs  P. Courtois  T. Courvoisier  M. Harris  M. Hernanz  J. Isern  P. Jean  J. Knödlseder  G. Skinner  B. Smither  P. Ubertini  G. Vedrenne  G. Weidenspointner  C. Wunderer 《Experimental Astronomy》2005,20(1-3):269-278

The next generation of instrumentation for nuclear astrophysics will have to achieve a factor of 10–100 improvement in sensitivity over present technologies. With the focusing gamma-ray telescope MAX we take up this challenge: combining unprecedented sensitivity with high spectral and angular resolution, and the capability of measuring the polarization of the incident photons. The feasibility of such a crystal diffraction gamma-ray lens has recently been demonstrated with the prototype lens CLAIRE. MAX is a proposed mission which will make use of satellite formation flight to achieve 86 m focal length, with the Laue lens being carried by one satellite and the detector by the other. In the current design, the Laue diffraction lens of MAX will consist of 13740 copper and germanium (Ge_1−x Si _x , x ∼ 0.02) crystal tiles arranged on 36 concentric rings. It simultaneously focuses in two energy bands, each centred on one of the main scientific objectives of the mission: the 800–900 keV band is dedicated to the study of nuclear gamma-ray lines from type Ia supernovae (e.g. ⁵⁶ Co decay line at 847 keV) while the 450–530 keV band focuses on electron-positron annihilation (511 keV emission) from the Galactic centre region with the aim of resolving potential point sources. MAX promises a breakthrough in the study of point sources at gamma-ray energies by combining high narrow-line sensitivity (better than 10⁻⁶ cm⁻² s⁻¹) and high energy resolution (E/dE ∼ 500). The mission has successfully undergone a pre-phase A study with the French Space Agency CNES, and continues to evolve: new diffracting materials such as bent or composite crystals seem very promising. PACS: 95.55.Ka, 29.30.Kv, 61.10.-i  相似文献   

Variations of the Wake Height over the Bolund Escarpment Measured by a Scanning Lidar     

Julia Lange  Jakob Mann  Nikolas Angelou  Jacob Berg  Mikael Sjöholm  Torben Mikkelsen 《Boundary-Layer Meteorology》2016,159(1):147-159

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On the effects of constraining atmospheric circulation in a coupled atmosphere-ocean Arctic regional climate model     

Peter Berg  Ralf Döscher  Torben Koenigk 《Climate Dynamics》2016,46(11-12):3499-3515

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A machine learning approach for regional geochemical data:Platinum-group element geochemistry vs geodynamic settings of the North Atlantic Igneous Province     

Jordan J. Lindsay  Hannah S.R. Hughes  Christopher M. Yeomans  Jens C.Ø. Andersen  Iain McDonald 《地学前缘(英文版)》2021,12(3):101098

Whilst traditional approaches to geochemistry provide valuable insights into magmatic processes such as melting and element fractionation, by considering entire regional data sets on an objective basis using machine learning algorithms(MLAs), we can highlight new facets within the broader data structure and significantly enhance previous geochemical interpretations.The platinum-group element(PGE) budget of lavas in the North Atlantic Igneous Province(NAIP) has been shown to vary systematically according to age, geographic location and geodynamic environment.Given the large multi-element geochemical data set available for the region, MLAs were employed to explore the magmatic controls on these shifting concentrations.The key advantage of using machine learning in analysis is its ability to cluster samples across multi-dimensional(i.e., multi-element)space.The NAIP data set is manipulated using Principal Component Analysis(PCA) and t-Distributed Stochastic Neighbour Embedding(t-SNE) techniques to increase separability in the data alongside clustering using the k-means MLA.The new multi-element classification is compared to the original geographic classification to assess the performance of both approaches.The workflow provides a means for creating an objective high-dimensional investigation on a geochemical data set and particularly enhances the identification of metallogenic anomalies across the region.The techniques used highlight three distinct multi-element end-members which successfully capture the variability of the majority of elements included as input variables.These end-members are seen to fluctuate in prominence throughout the NAIP, which we propose reflects the changing geodynamic environment and melting source.Crucially, the variability of Pt and Pd are not reflected in MLA-based clustering trends, suggesting that they vary independently through controls not readily demonstrated by the NAIP major or trace element data structure(i.e., other proxies for magmatic differentiation).This data science approach thus highlights that PGE(here signalled by Pt/Pd ratio) may be used to identify otherwise localised or cryptic geochemical inputs from the subcontinental lithospheric mantle(SCLM) during the ascent of plume-derived magma, and thereby impact upon the resulting metallogenic basket.  相似文献   

Accurate masses and radii of normal stars: modern results and applications     

G. Torres  J. Andersen  A. Giménez 《Astronomy and Astrophysics Review》2010,18(1-2):67-126

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Modelling of landslides with the material-point method   总被引：2，自引：0，他引：2  

S. Andersen  L. Andersen 《Computational Geosciences》2010,14(1):137-147

A numerical model for studying the dynamic evolution of landslides is presented. The numerical model is based on the Generalized Interpolation Material Point Method. A simplified slope with a house placed on top is analysed. An elasto-plastic material model based on the Mohr–Coulomb yield criterion is employed for the soil. The slide is triggered for the initially stable slope by removing the cohesion of the soil and the slide is followed from the triggering until a state of static equilibrium is again reached. Parameter studies, in which the angle of internal friction of the soil and the degree of discretisation are varied, are presented.  相似文献   

A diatom record of recent environmental change in Lake Duluti, northern Tanzania     

Helena ?berg  Thorbj?rn J. Andersen  Lars-Ove Westerberg  Jan Risberg  Karin Holmgren 《Journal of Paleolimnology》2012,48(2):401-416

Lake Duluti is a small, topographically closed crater lake located on the flanks of Mt Meru, northern Tanzania. Analyses of diatoms in three short sediment cores and four modern samples from Lake Duluti were used to infer past environmental changes. ²¹⁰Pb and ¹³⁷Cs activity profiles combined with AMS ¹⁴C dates provide the chronological framework. Weak agreement between the ²¹⁰Pb and ¹⁴C records, together with dating uncertainty, precludes construction of precise age models. The modern diatom flora, from plankton and three periphytic habitats, is dominated by Aulacoseira ambigua (Grunow) Simonsen, Gomphonema parvulum (Kützing) Grunow and Nitzschia amphibia Grunow. All three cores display similar stratigraphic succession, but the relative ratio of habitats represented by the diatoms varies substantially between cores. Diatoms indicate that the oldest part of the record is characterized by relatively low lake level and swampy vegetation. In the late nineteenth or early twentieth century there was a rapid lake level rise and the swamp turned into an open-water lake. High lake levels have prevailed since that time.  相似文献