Crystal field transitions in Co2[Al4Si5]O18 cordierite and CoAl2O4 spinel determined by neutron spectroscopy     

Björn Winkler  Mark J. Harris  Roger S. Eccleston  Karsten Knorr  Bernard Hennion 《Physics and Chemistry of Minerals》1997,25(1):79-82

Inelastic magnetic neutron scattering has been used to determine the energy of the ⁴ A ₂→⁴ T ₂ transition in CoAl₂O₄ spinel and the δ₁ transition in Co₂[Al₄Si₅]O₁₈ cordierite. The observed crystal field splitting in Co-spinel is 485 meV (3900 cm⁻¹), which corresponds to a crystal field stabilization energy of 56.2 kJmol⁻¹. The transition energy of the δ₁ transition in Co-cordierite has been determined to be 21 meV (170 cm⁻¹). The present data demonstrate that magnetic neutron scattering can be used to measure crystal field transitions at energies of interest in the study of 3d-containing silicates. It may be used to measure transition energies when the use of optical spectroscopy is inappropriate. Received: 30 January 1997 / Accepted: 5 July 1997  相似文献   

The crustal role of the Agulhas Plateau, southwest Indian Ocean: evidence from seismic profiling   总被引：2，自引：1，他引：2  

Karsten Gohl  Gabriele Uenzelmann-Neben 《Geophysical Journal International》2001,144(3):632-646

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DMS oxidation and turbulent transport in the marine boundary layer: A numerical study     

Karsten Suhre  Robert Rosset 《Journal of Atmospheric Chemistry》1994,18(4):379-395

DMS oxidation in the marine boundary layer has been simulated with a mesoscale meteorological model including detailed physical parameterizations. The impact of vertical turbulent transport on the DMS and SO₂ diurnal cycles with and without in-cloud SO₂ oxidation has been studied in a one-dimensional version of the model and compared to results obtained with a zero-dimensional box model. Initialisation has been done using balanced values issued from the imposed sea-air fluxes, dry deposition fluxes and chemical source/sink terms. Particular emphasis has been put on the important role played by evolving vertical mixing in the marine boundary layer.  相似文献   

Global Warming and the Summertime Evapotranspiration Regime of the Alpine Region   总被引：1，自引：0，他引：1  

Pierluigi Calanca  Andreas Roesch  Karsten Jasper  Martin Wild 《Climatic change》2006,79(1-2):65-78

Changes of the summer evapotranspiration regime under increased levels of atmospheric greenhouse gases are discussed for three Alpine river basins on the basis of a new set of simulations carried out with a high-resolution hydrological model. The climate change signal was inferred from the output of two simulations with a state-of-the-art global climate model (GCM), a reference run valid for 1961–1990 and a time-slice simulation valid for 2071–2100 under forcing from the A2 IPCC emission scenario. In this particular GCM experiment and with respect to the Alpine region summer temperature was found to increase by 3 to 4 ^∘C, whereas precipitation was found to decrease by 10 to 20%. Global radiation and water vapor pressure deficit were found to increase by about 5% and 2 hPa, respectively. On this background, an overall increase of potential evapotranspiration of about 20% relative to the baseline was predicted by the hydrological model, with important variations between but also within individual basins. The results of the hydrological simulations also revealed a reduction in the evapotranspiration efficiency that depends on altitude. Accordingly, actual evapotranspiration was found to increase at high altitudes and to the south of the Alps, but to decrease in low elevation areas of the northern forelands and in the inner-Alpine domain. Such a differentiation does not appear in the GCM scenario, which predicts an overall increase in evapotranspiration over the Alps. This underlines the importance of detailed simulations for the quantitative assessment of the regional impact of climate change on the hydrological cycle.  相似文献   

The importance of alternative conceptual models for simulation of concentrations in a multi-aquifer system     

Lars Troldborg  Jens Christian Refsgaard  Karsten Høgh Jensen  Peter Engesgaard 《Hydrogeology Journal》2007,15(5):843-860

Four different conceptual models based on alternative geological interpretations were formulated for a shallow 600 km² aquifer system in Denmark comprising Quaternary deposits. Each of the four models was calibrated against groundwater heads and discharge measurements through inverse modeling. Subsequently, the transport capabilities of the four models were compared to 32 concentration measurements of environmental tracers (tritium ³H, helium-3 ³He, chlorofluorocarbons CFC11, CFC12 and CFC113). The flow simulations showed only minor differences in spatial head distribution associated with alternative conceptualizations despite the complexity of the aquifer system and the significant differences in geological interpretations. The models, however, showed major differences in predictions of the age of the groundwater and environmental tracer concentrations, differences that are seen as an effect of model structure uncertainty, because no additional calibrations to these data were performed. A single conceptualization may be adequate in characterizing the natural behavior of a field system after calibration, because the calibration procedure is able to compensate for errors in the data or in the conceptual model through biased parameter values. However, once extrapolation beyond the calibration base is attempted, different conceptual model formulations result in significantly different results. Consequently, it is crucial to take model conceptual uncertainty into account when making predictions beyond the calibration base.  相似文献   

Gottfried Konecny:The photogrammetric and remote sensing trend setter     

Karsten Jacobsen 《地球空间信息科学学报》2021,24(1):13-21

PREFACE There are various publications on the 90th birthday of Gottfried Konecny.His involvement in the International Society for Photogrammetry and Remote Sensing(ISPRS)is particularly described by others.Here,his forward-oriented impulses in research and development at the former Institute for Photogrammetry and Engineering Survey of the(Technical)University of Hannover,today Institute for Photogrammetry and Geoinformation,Leibniz University Hannover,and some of his activities supporting developing and other countries by given short-term courses are highlighted.Gottfried Konecny was always one of the first in pushing new technologies.With the analytical plotter AP/C-3,he introduced analytical photogrammetry in Germany.Based on his experience with this not really operational version,he induced the company Zeiss to develop the first really operational analytical plotter Planicomp,which resulted in the end of analog photogrammetric devices and their limitations.At the invitation of Gilbert Hobrough,a mainly hardware-based image correlator was developed for the AP/C-3 in Hannover which anticipated many of today's applications.Gottfried Konecny initiated remote sensing in Germany.Based on his proposal with the Metric Camera Flight on Spacelab,the then highest resolution civil stereoscopic space images available were generated.Despite limited computer performance at his institute,a digital stereo plotter was developed,using hardware components from the cooperating Swedish company Context Vision,long before digital stereo workstations with increased and affordable computer capacity were possible.Also,in the area of GIS,he too,pushed development in collaboration with companies and administrations.Shortly before the end of his time as head of the institute,and more so after he became emeritus professor,he started a series of educational workshops,particularly in developing countries,but also other countries,to support the development of photogram-metry,remote sensing and GIS.He promoted the use of space imagery for mapping to improve the situation of poorly updated topographic maps.  相似文献   

Investigation of the Ablation Behaviour of Andradite-Grossular Garnets and Rutile with Implications for U-Pb Geochronology     

Kate Jenkins  Karsten Goemann  Ivan Belousov  Maxwell Morissette  Leonid Danyushevsky 《Geostandards and Geoanalytical Research》2023,47(2):267-295

U-Pb dating of andradite-grossular garnet (grandite) and rutile by LA-ICP-MS can be used to constrain various metamorphic, metasomatic and igneous geological processes. In this study, we examine and compare the impact of different analytical conditions (fluence, pulse width, laser beam size and ablation frequency) on the ablation crater morphology, ablation rates, down-hole fractionation and U-Pb ages of grandite and rutile samples of different compositions. The shapes of grandite ablation craters suggest the mineral ablates by classical evaporation with significant melting that cannot be eliminated even at fluences just above the ablation threshold. Grandite garnets with higher andradite proportions have faster ablation rates. The overall low U contents of grandite require using large laser beam sizes to obtain acceptable precision of U-Pb ages. At such conditions and crater depths < 10 μm, fluences of 2.1 and 3.5 J cm^-2, laser pulse width of 5 ns and 20 ns, and ablation frequencies between 3.5 and 6.5 Hz, obtain similar and reproducible ages when the proportion of grossular is < 35%. Rutile ablation crater morphology shows evidence of melt splashing and thermal stress cracking. They have significant crater bottom features, which increase in relief with lower fluences and a higher number of laser shots, indicating the features are probably energy-related and making higher fluences, such as 5 J cm^-2, necessary for uniform ablation when using 193 nm excimer lasers. The slow ablation rate at low fluences and then steep increase at around 2.0 J cm^-2 suggests a transition in the ablation mechanism from exfoliation to classical vaporisation. Crater bottom features and other ablation behaviour vary between samples, which could be related to their difference in colour. Although the down-hole fractionation patterns of the samples are similar at 5 J cm^-2, the U-Pb ages of some samples vary significantly with different analytical conditions and/or measurement sessions, particularly when using laser beam sizes of 30 μm, suggesting differences in mass bias and more variable ablation behaviour. A laser beam size of at least 60 μm is recommended for reproducible U-Pb dating of rutile.  相似文献   

STDGL3, a Reference Material for Analysis of Sulfide Minerals by Laser Ablation ICP-MS: An Assessment of Matrix Effects and the Impact of Laser Wavelengths and Pulse Widths     

Ivan Belousov  Leonid Danyushevsky  Karsten Goemann  Sarah Gilbert  Paul Olin  Jay Thompson  Elena Lounejeva  Dieter Garbe-Schönberg 《Geostandards and Geoanalytical Research》2023,47(3):493-508

A new reference material, STDGL3, for the calibration of in situ analyses of sulfide minerals by LA-ICP-MS has been developed and characterised. It represents a lithium-borate-based glass containing a mixture of Zn- and Fe-sulfide concentrates doped with several chalcophile elements as well as Zr, Gd, Hf and Ta required for assessing common interferences on Ag, Au and Pt. STDGL3 has a wider range of elements and a better homogeneity compared with existing reference materials for LA-ICP-MS analysis of sulfides. Compositional variations for most elements are below 3% RSD, below 5% RSD for Ag, Au and Pt, and below 7% RSD for Se, when performing spot analyses with a 50 μm beam size. Its preparation recipe is reproducible allowing for multiple batches to be made. Use of STDGL3 significantly improves accuracy of sulfide mineral analysis by LA-ICP-MS when compared with use of other available reference materials. Performance of STDGL3 was evaluated using several different laser systems. No significant change was observed between 193 nm ArF excimer lasers with 5 and 20 ns pulse widths, but use of 213 and 248 nm lasers displays more systematic differences, especially when analysing galena. Correction coefficients are needed for some elements (Zn and Cd in particular) when analysing sulfide minerals using STDGL3 as a calibration reference material.  相似文献   

Assessing vertical diffusion in a stratified lake using a three-dimensional hydrodynamic model     

Fei Dong  Chenxi Mi  Michael Hupfer  Karl-Erich Lindenschmidt  Wenqi Peng  Xiaobo Liu  Karsten Rinke 《水文研究》2020,34(5):1131-1143

Vertical turbulent diffusivity (K_z), which can be estimated from water temperature, is a key factor in the evolution of water quality in lentic waters. In this study, we analysed the capability of a three-dimensional hydrodynamic model (EFDC) to capture water temperature and vertical diffusivity in Lake Arendsee in the Northern German plain. Of particular interest to us is to evaluate the model performance for capturing the diffusion minimum within the metalimnion and analyse the response of the metalimnetic K_z to meteorological forcing, namely changing wind speed and warming. The comparison confirmed that the calibrated model could reproduce both stratification dynamics and vertical diffusion profiles in the lake. The model was also shown to be able to capture the duration and vertical extent of the metalimnetic diffusion minimum. The scenario results illustrate that, compared to air temperature, wind velocity appeared to be the more influential meteorological variable on the vertical exchange within the metalimnion. While increasing wind velocities mostly affected the minimum values of K_z in the metalimnion and thus led to intensified vertical exchange, the reduction of wind velocity mostly affected the depth of minimal K_z, but not its absolute value.  相似文献   

Tectonic controls on Miocene sedimentation in the Southern Taranaki Basin and implications for New Zealand plate boundary deformation     

Suzanne Bull  Andrew Nicol  Dominic Strogen  Karsten F. Kroeger  Hannu S. Seebeck 《Basin Research》2019,31(2):253-273

Miocene strata in the southern Taranaki Basin (STB), up to 3 km thick, provide a distal record of erosion associated with plate boundary deformation in New Zealand. 2D and 3D seismic reflection data tied to drillhole stratigraphy have been used to constrain four main phases of basin development. These are: (a) Early Miocene (22–19 Ma) subsidence, dominantly bathyal water depths and deposition of minor submarine fans along the eastern basin margin. (b) Middle Miocene (19–14 Ma) widespread submarine fan deposition on a bathyal basin floor in the central STB. (c) Rapid Middle–Late Miocene (14–7 Ma) progradation of the shelf break northwards across the STB. (d) Widespread uplift and erosion of the STB during the latest Miocene–Pliocene (7–4.5 Ma). Bathyal water depths and fan deposition in the Early Miocene were influenced by vertical motions on major reverse faults and regional subsidence produced by subduction of the Pacific plate beneath northern New Zealand. Subsequent submarine fan deposition and northward shelf‐break progradation reflect increasing input of terrigenous material, primarily eroded from an uplifting region to the south of the STB. Sedimentation patterns in the STB are consistent with the age and locations of conglomerates deposited in onshore West Coast basins, related to this uplift and erosion. Sediment transport in the West Coast region was mainly parallel to NNE trending active reverse faults, and in the STB was perpendicular to the NE‐SW orientated shelf break, especially from ca. 14–7 Ma, when sedimentation rates exceeded fault‐displacement rates. Increases in sedimentation rates in the STB coincide with regional increases in the rates of shortening that appear to reflect plate boundary‐wide events and have been attributed to, or correlated with, increases in the plate convergence rate. Miocene sedimentation patterns in the STB thus reflect both intra‐basinal deformation and tectonic signals from the wider developing New Zealand plate boundary.  相似文献