Lagrangian modelling of dispersion,sedimentation and resuspension processes in marine environments     

Lars Gidhagen  Dr. Lars Rahm  Leif Nyberg 《Ocean Dynamics》1989,42(3-6):249-270

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A simple method of quantifying filamentous algae in microscope     

Lars Ramberg 《Aquatic Sciences - Research Across Boundaries》1988,50(2):189-192

A fast and simple method to quantify filamentous algae in inverted microscope is described. It is based on the number of intersections between the midline of a diametrical transect and the filaments on the chamber bottom. It is shown to be theoretically sound and is compared with the common length measurement method.  相似文献   

Thermodynamics, structure, dynamics, and freezing of Mg₂SiO₄ liquid at high pressure     

Nico P. de Koker  Lars Stixrude  Bijaya B. Karki 《Geochimica et cosmochimica acta》2008,72(5):1427-1441

We perform first principles molecular dynamics simulations of Mg₂SiO₄ liquid and crystalline forsterite. On compression by a factor of two, we find that the Grüneisen parameter of the liquid increases linearly from 0.6 to 1.2. Comparison of liquid and forsterite equations of state reveals a temperature-dependent density crossover at pressures of ∼12-17 GPa. Along the melting curve, which we calculate by integration of the Clapeyron equation, the density crossover occurs within the forsterite stability field at P = 13 GPa and T = 2550 K. The melting curve obtained from the root mean-square atomic displacement in forsterite using the Lindemann law fails to match experimental or calculated melting curves. We attribute this failure to the liquid structure that differs significantly from that of forsterite, and which changes markedly upon compression, with increases in the degree of polymerization and coordination. The mean Si coordination increases from 4 in the uncompressed system to 6 upon twofold compression. The self-diffusion coefficients increase with temperature and decrease monotonically with pressure, and are well described by the Arrhenian relation. We compare our equation of state to the available highpressure shock wave data for forsterite and wadsleyite. Our theoretical liquid Hugoniot is consistent with partial melting along the forsterite Hugoniot at pressures 150-170 GPa, and complete melting at 170 GPa. The wadsleyite Hugoniot is likely sub-liquidus at the highest experimental pressure to date (200 GPa).  相似文献   

CODE’s five-system orbit and clock solution—the challenges of multi-GNSS data analysis   总被引：1，自引：1，他引：0  

Lars Prange  Etienne Orliac  Rolf Dach  Daniel Arnold  Gerhard Beutler  Stefan Schaer  Adrian Jäggi 《Journal of Geodesy》2017,91(4):345-360

This article describes the processing strategy and the validation results of CODE’s MGEX (COM) orbit and satellite clock solution, including the satellite systems GPS, GLONASS, Galileo, BeiDou, and QZSS. The validation with orbit misclosures and SLR residuals shows that the orbits of the new systems Galileo, BeiDou, and QZSS are affected by modelling deficiencies with impact on the orbit scale (e.g., antenna calibration, Earth albedo, and transmitter antenna thrust). Another weakness is the attitude and solar radiation pressure (SRP) modelling of satellites moving in the orbit normal mode—which is not yet correctly considered in the COM solution. Due to these issues, we consider the current state COM solution as preliminary. We, however, use the long-time series of COM products for identifying the challenges and for the assessment of model-improvements. The latter is demonstrated on the example of the solar radiation pressure (SRP) model, which has been replaced by a more generalized model. The SLR validation shows that the new SRP model significantly improves the orbit determination of Galileo and QZSS satellites at times when the satellite’s attitude is maintained by yaw-steering. The impact of this orbit improvement is also visible in the estimated satellite clocks—demonstrating the potential use of the new generation satellite clocks for orbit validation. Finally, we point out further challenges and open issues affecting multi-GNSS data processing that deserves dedicated studies.  相似文献   

A method for estimating sediment budgets of washover deposits using digital terrain models     

Lars Ø. Hansen  Verner B. Ernstsen  Lars B. Clemmensen  Zyad Al-Hamdani  Aart Kroon 《地球表面变化过程与地形》2021,46(4):804-821

Washover fans are located on small barriers in fetch-limited micro-tidal coastal environments in Denmark. These washover fans are formed during high-energy storm events and we present a method to quantify their volumes and to estimate sediment exchanges between washover fans and their adjacent morphologies. We use high resolution digital terrain models (DTMs) based on light detection and ranging (LiDAR) data. We have delineated landforms using known methods of scale analysis and geomorphometric classification. We quantified volumes of the delineated landforms and estimated the related sediment budgets. These computed volumes were compared using different pre-depositional surfaces. Finally, we assessed the sediment exchange and associated sources of sediments of the washover fans. We applied a scale analysis to determine suitable DTM resolution and focal statistics window size as input to a geomorphometric classification analysis. Landform areas and landforms were delineated using morphometric threshold values, and volumes and sediment budgets of the delineated landforms were computed using different assumptions to define the pre-depositional surface. Resulting washover fan volumes were validated against digital elevation model (DEM) of difference (DoD) derived volumes. Sediment budgets were derived from representative volumes of the washover fans and adjacent berms. We show that quantification of washover features derived from DTMs, using geomorphometric analysis is feasible and that the presented approach provides estimates of washover deposit volumes with an accuracy between 1% and 28% compared to control volumes. © 2021 John Wiley & Sons, Ltd.  相似文献   

Crystallization sequence of the Upper Border Series of the Skaergaard Intrusion: revised subdivision and implications for chamber-scale magma homogeneity     

Lars Peter Salmonsen  Christian Tegner 《Contributions to Mineralogy and Petrology》2013,165(6):1155-1171

Although it is one of the best-studied layered mafic intrusions in the world, the crystallization sequence of the Skaergaard Intrusion, east Greenland, remains in debate. In particular, it has been argued that the crystallization sequence in the Upper Border Series, which crystallized downwards from the roof of the magma chamber, differs from that in the Layered Series formed at the floor. The proposed deviation would require chemical stratification of the magma, and a reexamination of the crystallization sequence therefore has important implications for understanding the dynamics of the system. Here, we examine a new sample set from the Upper Border Series, combining field observations, petrography and anorthite contents of plagioclase with bulk rock Ti, V, P, Cu and Mn concentrations. We demonstrate that the first phases on the liquidus were plagioclase and olivine followed by augite, then ilmenite and magnetite (simultaneously), sulfides, apatite and finally ferrobustamite (now inverted to hedenbergite). This crystallization sequence represents extreme differentiation along the tholeiitic trend, and it mirrors those at the floor (Layered Series) and walls (Marginal Border Series). We therefore propose a revised subdivision of the Upper Border Series into equivalents of the subzones in the Layered Series denoted by apostrophes (LZa′, LZb′, etc.). Moreover, the first appearance of each of the cumulus phases occurs at similar plagioclase core anorthite contents. The mirror images of the crystallization sequences and the anorthite contents of plagioclase cores in the three series imply that the Skaergaard magma chamber solidified by in situ crystallization along the floor, walls and roof from one, largely homogenous, convecting magma body.  相似文献   

Catchments as reactors: a comprehensive approach for water fluxes and solute turnover   总被引：1，自引：1，他引：0  

Peter Grathwohl  Hermann Rügner  Thomas Wöhling  Karsten Osenbrück  Marc Schwientek  Sebastian Gayler  Ute Wollschläger  Benny Selle  Marion Pause  Jens-Olaf Delfs  Matthias Grzeschik  Ulrich Weller  Martin Ivanov  Olaf A. Cirpka  Ulrich Maier  Bertram Kuch  Wolfgang Nowak  Volker Wulfmeyer  Kirsten Warrach-Sagi  Thilo Streck  Sabine Attinger  Lars Bilke  Peter Dietrich  Jan H. Fleckenstein  Thomas Kalbacher  Olaf Kolditz  Karsten Rink  Luis Samaniego  Hans-Jörg Vogel  Ulrike Werban  Georg Teutsch 《Environmental Earth Sciences》2013,69(2):317-333

Sustainable water quality management requires a profound understanding of water fluxes (precipitation, run-off, recharge, etc.) and solute turnover such as retention, reaction, transformation, etc. at the catchment or landscape scale. The Water and Earth System Science competence cluster (WESS, http://www.wess.info/) aims at a holistic analysis of the water cycle coupled to reactive solute transport, including soil–plant–atmosphere and groundwater–surface water interactions. To facilitate exploring the impact of land-use and climate changes on water cycling and water quality, special emphasis is placed on feedbacks between the atmosphere, the land surface, and the subsurface. A major challenge lies in bridging the scales in monitoring and modeling of surface/subsurface versus atmospheric processes. The field work follows the approach of contrasting catchments, i.e. neighboring watersheds with different land use or similar watersheds with different climate. This paper introduces the featured catchments and explains methodologies of WESS by selected examples.  相似文献   

Strategic assessment of fuel taxation in energy conservation and CO2 reduction for road transportation: a case study from China     

Yutao Wang  Lars Hansson  Nan Sha  Yanqiang Ding  Renqing Wang  Jian Liu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(5):1231-1238

Road transportation has attracted extensive attention throughout the world because of its high energy demands and numerous externalities. Sustainable road transportation has thus become a great challenge for politicians and decision-makers all over the world. There have been a series of studies indicating that appropriate pricing of fuel can be both effective and efficient for reducing overconsumption of transport fuel. However, relatively little research has been done on fuel price approaches in developing country contexts. For a country like China, where road traffic today is growing more than in other countries, there is a strategic interest to do more economic analyses of fair and efficient pricing of fuel. In this study, we present a strategic assessment of fuel pricing in energy conservation and CO₂ reduction from road transportation in China, both in a retrospective and a prospective perspective. First of all, the correlation between fuel price and road transport gasoline demand, based upon data from 1995 to 2007, was examined with an econometric model. Secondly, on basis of the elasticity model, the potential reductions with respect to fuel demand and Green House Gas (GHG) emissions as a consequence of a strategic fuel tax implementation in China were examined up to 2030. The results indicate that such strategic fuel taxation can play a considerable role in steering the growth of road transport gasoline demand, and thus also Chinese GHG emissions.  相似文献   

Documentation and evaluation of the CSE NOAA AVHRR data set     

Gorm Dybkjær  Thomas Theis Nielsen  Kjeld Rasmussen  Michael Schultz Rasmussen  Lars Boye Hansen  Assize Touré 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):125-135

A NOAA AVHRR data set covering Senegal and parts of the surrounding countries during the period from 1987 to present is under construction and improvement in an ongoing collaboration between Centre de Suivi Écologique (CSE). Dakar. Senegal, and Institute of Geography, University of Copenhagen (IGUC). This paper details the entire processing chain from raw images to a properly calibrated, geometrically rectified and cloud-masked time-series tracking a number of well-defined variables. Two vital aspects of this time series, the cloud masking procedure and the geometrical rectification, are evaluated in detail. A two-step, multi-criteria cloud masking procedure requiring a manual input does not consistently improve the quality of the data set compared to the simpler, automated procedure. With respect to geometrical rectification an accuracy on the order of I km is obtained. Finally, suggestions for further improving the data set are forwarded  相似文献   

A soil description system for burial mounds—development and application     

Lars C. Lund-Hansen  Christian Christiansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):37-45

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