Sequestration of CO₂ after reaction with alkaline earth metal oxides CaO and MgO     

Martin Back  Markus BauerHelge Stanjek  Stefan Peiffer 《Applied Geochemistry》2011,26(7):1097-1107

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Characteristics of a paleosol and its implication for the Critical Zone development,Rocky Mountain Front Range of Colorado,USA     

Matthias Leopold  Jörg Völkel  David Dethier  Juliane Huber  Markus Steffens 《Applied Geochemistry》2011

Activity and stability phases as well as geomorphic processes within the Critical Zone are well known. Erosion and deposition of sediments represent activity; soils represent geomorphic stability phases. Data are presented from a 4 m deep sediment section that was dated by luminescence techniques. Upslope erosion and resulting sedimentation started in the late Pleistocene around 18 ka until 12 ka. Conditions at the study site then changed, which led to the formation of a well-developed soil. Radiocarbon dating of the organic matter yielded ages between 8552 and 8995 cal. BP. From roughly 6.2 to 5.4 ka another activity phase accompanied by according sediment deposition buried the soil and a new soil, a Cambisol, was formed at the surface. The buried soil is a strongly developed Luvisol. The black colors in the upper part of the buried soil are not the result of pedogenic accumulation of normal organic matter within an A-horizon. Nuclear magnetic resonance spectroscopy clearly documents the high amount of aromatic components (charcoal), which is responsible for the dark color. This indicates severe burning events at the site and the smaller charcoal dust (black carbon) was transported to deeper parts of the profile during the process of clay translocation.  相似文献   

Effects of molecular mass on the diffusion coefficient in a multiphase lattice Boltzmann model     

Elizabeth B. Liu  Markus Hilpert 《Computational Geosciences》2011,15(3):379-384

We introduce a simplified expression for the diffusion coefficient (D) of a multicomponent Lattice Boltzmann model. For dilute solutions, this expression is reduced to have dependence only on the molecular mass and relaxation time of the solute. By altering the molecular mass, the value of D can be varied by several orders of magnitude, thus, providing an additional parameter for use in tuning LB model values to physical systems. The ability to adjust the values of molecular mass can also be used to decrease simulation times. This is advantageous as it allows application of the LB model to solve problems that previously required prohibitive computational resources. The capability to model a wide range of diffusion coefficients and decrease simulation times is illustrated in a simple case study.  相似文献   

Coastal Mediterranean plankton stimulation dynamics through a dust storm event: An experimental simulation     

Estela Romero  Francesc Peters  Cèlia Marrasé  Òscar Guadayol  Josep M. Gasol  Markus G. Weinbauer 《Estuarine, Coastal and Shelf Science》2011

An enhancement of aeolian inputs to the ocean due to a future increase in aridity in certain parts of the world is predicted from global change. We conducted an experimental simulation to assess the biological response of NW Mediterranean coastal surface waters to an episodic dust addition. On the assumption that planktonic growth was limited by phosphorus, dust effects were compared to those induced by equivalent enrichments of phosphate. The experiment analyzed the dynamics of several parameters during one week: inorganic nutrients, total and fractioned chlorophyll a, bacterial abundance, phytoplankton species composition, abundance of autotrophic and heterotrophic flagellates, particulate organic carbon and particulate organic nitrogen. The maximum addition of dust (0.5 g dust L⁻¹) initiated an increase in bacterial abundance. After 48 h, bacterial numbers decreased due to a peak in heterotrophic flagellates and a significant growth of autotrophic organisms, mainly nanoflagellates but also diatoms, was observed. Conversely, lower inputs of dust (0.05 g dust L⁻¹) and phosphate enrichments (0.5 μmol PO₄³⁻ L⁻¹) only produced increases in phototrophic nanoflagellates. In our experiment, dust triggered bacterial growth, changed phytoplankton dynamics and affected the ratio of autotrophic to heterotrophic biomass, adding to the variability in the sources that affect system dynamics, energy and carbon budgets and ultimately higher trophic levels of the coastal marine food web.  相似文献   

On the Photometric Accuracy of RHESSI Imaging and Spectrosocopy     

Aschwanden  Markus J.  Metcalf  Thomas R.  Krucker  Säm  Sato  Jun  Conway  Andrew J.  Hurford  G.J.  Schmahl  Edward J. 《Solar physics》2004,219(1):149-157

We compare the photometric accuracy of spectra and images in flares observed with the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft. We test the accuracy of the photometry by comparing the photon fluxes obtained in different energy ranges from the spectral-fitting software SPEX with those fluxes contained in the images reconstructed with the Clean, MEM, MEM-Vis, Pixon, and Forward-fit algorithms. We quantify also the background fluxes, the fidelity of source geometries, and spatial spectra reconstructed with the five image reconstruction algorithms. We investigate the effects of grid selection, pixel size, field of view, and time intervals on the quality of image reconstruction. The detailed parameters and statistics are provided in an accompanying CD-ROM and web page. We find that Forward-fit, Pixon, and Clean have a robust convergence behavior and a photometric accuracy in the order of a few percent, while MEM does not converge optimally for large degrees of freedom (for large field of view and/or small pixel sizes), and MEM-Vis suffers in the case of time-variable sources. This comparative study documents the current status of the RHESSI spectral and imaging software, one year after launch. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/B:SOLA.0000021801.83038.aa  相似文献   

More evidence that the Chicxulub impact predates the K/T mass extinction     

Gerta KELLER  Thierry ADATTE  Wolfgang STINNESBECK  Doris STüBEN  Zsolt BERNER  Utz KRAMAR  Markus HARTING 《Meteoritics & planetary science》2004,39(7):1127-1144

Abstract Yaxcopoil‐1 (Yax‐1), drilled within the Chicxulub crater, was expected to yield the final proof that this impact occurred precisely 65 Myr ago and caused the mass extinction at the Cretaceous‐Tertiary (K/T) boundary. Instead, contrary evidence was discovered based on five independent proxies (sedimentologic, biostratigraphic, magnetostratigraphic, stable isotopic, and iridium) that revealed that the Chicxulub impact predates the K/T boundary by about 300,000 years and could not have caused the mass extinction. This is demonstrated by the presence of five bioturbated glauconite layers and planktic foraminiferal assemblages of the latest Maastrichtian zone CF1 and is corroborated by magnetostratigraphic chron 29r and characteristic late Maastrichtian stable isotope signals. These results were first presented in Keller et al. (2004). In this study, we present more detailed evidence of the presence of late Maastrichtian planktic foraminifera, sedimentologic, and mineralogic analyses that demonstrate that the Chicxulub impact breccia predates the K/T boundary and that the sediments between the breccia and the K/T boundary were deposited in a normal marine environment during the last 300,000 years of the Cretaceous.  相似文献   

The search for extrasolar giant planets using integral field spectroscopy: Simulations     

Alessandro Berton  Markus Feldt  Raffaele Gratton  Stefan Hippler  Thomas Henning 《New Astronomy Reviews》2006,49(10-12):661

We present here simulations of extrasolar planets detections obtained using a combination of extreme adaptive optics and integral field spectroscopy. The simulation code, written for IDL, provides images and, in particular, spectra, taking into account realistic Speckle Noise, AO correction effects and specific instrumental features. A detailed study has been done for ESO VLT telescopes (8.2 m), within the Phase A of the CHEOPS project, but the code is particularly flexible and can be updated for larger telescope diameters (ELTs) in order to give a realistic estimate of the detection limits, for giant telescopes, in standard conditions of seeing.  相似文献   

Chromospheric Height and Density Measurements in a Solar Flare Observed with RHESSI – I. Theory     

Brown  John C.  Aschwanden  Markus J.  Kontar  Eduard P. 《Solar physics》2002,210(1-2):373-381

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Analysing large-scale structure – I. Weighted scaling indices and constrained randomization     

Christoph Räth  Wolfram Bunk  Markus B. Huber  Gregor E. Morfill  Jörg Retzlaff  Peter Schuecker 《Monthly notices of the Royal Astronomical Society》2002,337(2):413-421

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Cosmic rays at ultra high energies (Neutrinos!)     

Markus Ahlers  Andreas Ringwald  Huitzu Tu 《Astroparticle Physics》2006,24(6):438-450

Resonant photo-pion production with the cosmic microwave background predicts a suppression of extragalactic protons above the famous Greisen–Zatsepin–Kuzmin cutoff at about E_GZK ≈ 5 × 10¹⁰ GeV. Current cosmic ray data measured by the AGASA and HiRes Collaborations do not unambiguously confirm the GZK cutoff and leave a window for speculations about the origin and chemical composition of the highest energy cosmic rays. In this work we analyze the possibility of strongly interacting neutrino primaries and derive model-independent quantitative requirements on the neutrino–nucleon inelastic cross section for a viable explanation of the cosmic ray data. Search results on weakly interacting cosmic particles from the AGASA and RICE experiments are taken into account simultaneously. Using a flexible parameterization of the inelastic neutrino–nucleon cross section we find that a combined fit of the data does not favor the Standard Model neutrino–nucleon inelastic cross section, but requires, at 90% confidence level, a steep increase within one energy decade around E_GZK by four orders of magnitude. We illustrate such an enhancement within some extensions of the Standard Model. The impact of new cosmic ray data or cosmic neutrino search results on this scenario, notably from the Pierre Auger Observatory soon, can be immediately evaluated within our approach.  相似文献